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Jul 1969

Volume 6, Issue 4, pp. 439-787


Film Formation and Structure-Sensitive Properties—An Introduction

Klaus H. Behrndt

J. Vac. Sci. Technol. 6, 439 (1969); http://dx.doi.org/10.1116/1.1315651 (4 pages)

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The present state of knowledge regarding film formation permits only a qualitative picture of the processes. Reliable data on nucleation and growth are needed for a quantitative comparison between experiment and theory, taking into account the phase of the condensate, the influence of defects in the substrate surface, and so on. Furthermore, a correlation between the results of different methods is necessary for understanding their range of applicability. This information is a prerequisite for controlling film structure as well as the structure-sensitive properties so that film components can be fabricated reliably and reproducibly.
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81.15.Aa Theory and models of film growth
68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic

Film Formation and Structural Problems

D. S. Campbell

J. Vac. Sci. Technol. 6, 442 (1969); http://dx.doi.org/10.1116/1.1315652 (7 pages) | Cited 2 times

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A brief review of the present position on nucleation, growth, and epitaxy is given. With regard to nucleation and growth, the following main points are made: (1) The atomistic model of nucleation is conceptually the most useful; (2) Using the model, it has been shown that experimentally one is usually making measurements well after growth has taken over from nucleation; (3) Modifications to saturation island density calculations are being made that recognize the limitations of the original concept; (4) Work is in hand that attempts to correlate adhesion measurements with nucleation results. In the case of epitaxial growth, it is noted that: (1) Nuclei types are affected by the type of site and that the sites may be modified by various methods; (2) Sintering theory when applied to recrystallization shows that above a certain island size agglomeration will not eliminate defects; (3) The concept of effective supersaturation shows that such high values of supersaturation are normally present that there is insufficient time to anneal out faults developed in the growing film.
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81.15.Aa Theory and models of film growth
68.55.-a Thin film structure and morphology

Pitfalls in the Interpretation of Structure-Sensitive Properties

M. H. Francombe

J. Vac. Sci. Technol. 6, 448 (1969); http://dx.doi.org/10.1116/1.1315653 (7 pages)

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A clear understanding of the manner in which the properties of thin films respond to changes in structure or composition is an essential prerequisite both to controlling their characteristics and to using them in practical applications. Examples of studies on epitaxial elemental semiconductors are described to illustrate how ambiguities arise in characterizing growth mechanism, degrees of structural order, and transport behavior. Some of the causes and consequences of disorder and nonstoichiometry are discussed with reference to wide band-gap semiconductor compounds.
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68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic

Some Less Well-Known Structure-Property Relationships in Thin Films

C. A. Neugebauer

J. Vac. Sci. Technol. 6, 454 (1969); http://dx.doi.org/10.1116/1.1315654 (7 pages)

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Four thin film structure-property relationships, which are perhaps less well known than they deserve, will be discussed in this report. The first of these is associated with the temperature dependence of the carrier mobility in thin polycrystalline semiconductor films, which exhibit thermally activated behavior rather than following the T−3∕2 law. Second, a piezoelectric phenomenon is discussed, which depends on the fiber axis orientation frequently observed when II–VI compound films with hexagonal structure are deposited on glass substrates. Third, since thin films, metallic or semiconducting, frequently contain two or more phases, two examples have been picked in which the effect of the second phase drastically changes the properties. One of these involves a metallic phase in a high mobility semiconductor film, and the other a nonmetallic phase dispersed in a film of a binary alloy.
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77.55.-g Dielectric thin films

Nucleation and Surface Conditions

H. Bethge

J. Vac. Sci. Technol. 6, 460 (1969); http://dx.doi.org/10.1116/1.1315655 (8 pages) | Cited 7 times

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The nucleation of Ag and Au on alkali halides is discussed excluding the influence of adsorbed gas layers. In particular, the problems of nucleation density and of the orientation of nuclei with respect to the substrate crystal are treated. The influence of defects in the surface on nucleation density is discussed in detail. Some principal aspects necessary for a theoretical treatment are pointed out. A review of the problem of the orientation of nuclei is given. An explanation of some recent results, the possible influence of electrical double layers (Debye-Frenkel layers) in the surface region is discussed.
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81.15.Aa Theory and models of film growth

Point Imperfections and Epitaxy of Some fcc Metals

T. N. Rhodin, C. J. Todd, and P. W. Palmberg

J. Vac. Sci. Technol. 6, 467 (1969); http://dx.doi.org/10.1116/1.1315656 (1 page)

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It has been found that plane, line, and point imperfections play an important role in the incidence, alignment, and morphology characteristic of metal nuclei formed by heterogeneous condensations of heterogeneous vapor condensation involving relatively strong homogeneous interactions and weak heterogeneous interactions can now be applied to the mechanism of metal film formation with some confidence for specific metalsubstrate condensation systems. The high sensitivity of film orientation and structure to the initial stages of nucleation for these systems suggests that critical factors pertaining to the defect structure of the substrate and to the specific vacuum conditions prior to and during condensation influence film formation. For example, the low epitaxial temperature observed on irradiated surfaces indicates that epitaxial alignment of nuclei on ordered, tight-binding sites is critical in inducing epitaxy at low temperature. Some of the significant factors essential to the influence of these variables on the epitaxial growth of face-centered cubic metals on uhv-cleaved ionic substrates of alkali halides and metal oxides will be discussed in terms of the atomistic theory of nucleation. Recently completed experimental measurements of bulk and surface film crystallography, of surface chemical composition, of irradiation damage, and of film structure and continuity will be considered.
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81.15.Aa Theory and models of film growth

An Experimental Test of Nucleation Theory: Formation of Rare Gas Crystals

D. J. Ball and J. A. Venables

J. Vac. Sci. Technol. 6, 468 (1969); http://dx.doi.org/10.1116/1.1315657 (4 pages)

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In situ electron microscopic observations have been made upon the rare gas solids during nucleation on cooled graphite substrates. In particular, the saturation density of nuclei has been measured as a function of temperature and arrival rate with a view to testing current nucleation theory, as expounded by Walton. An important feature of this experiment is that the relevant parameters for these systems, such as surface diffusion and cluster energies, are known. Consequently it has been possible to make an absolute check on the theory, which is found to fit well, particularly when describing critical nuclei of small size.
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68.55.-a Thin film structure and morphology

Formation Processes of Vacuum-Deposited Indium Films and Thermodynamical Properties of Submicroscopic Particles Observed by In Situ Electron Microscopy

J. F. Pócza, A. Barna, and P. B. Barna

J. Vac. Sci. Technol. 6, 472 (1969); http://dx.doi.org/10.1116/1.1315658 (4 pages) | Cited 15 times

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The formation of vacuum-deposited In thin films was studied by in situ electron microscopy. The dependence of melting point and crystallization temperature on particle size was measured. A preferred orientation was found to develop at a given crystallite size depending on the substrate temperature and on the ratio of impinging oxygen molecules to film atoms (K factor).
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

The Initial Stages of Growth of a Metal Film on a Single-Crystal Metal Substrate

E. Grünbaum, G. Kremer, and C. Reymond

J. Vac. Sci. Technol. 6, 475 (1969); http://dx.doi.org/10.1116/1.1315659 (5 pages) | Cited 2 times

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The initial stages of growth of copper, nickel, and cobalt, deposited in ultrahigh vacuum onto a clean (111) silver single-crystal film have been studied by reflection high-energy electron diffraction in situ. Oriented nuclei and single-crystal films (with double positioning) were obtained for all substrate temperatures and thicknesses. No signs of a pseudomorphic growth were detected even in the thinnest deposits. The detection limit of the deposits was 0.05 Å. The sticking coefficient of the first metal nuclei on the substrate was determined as a function of substrate temperature. The present results differ considerably from those obtained previously in conventional high vacuum, demonstrating the influence of contaminants in the latter.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Anisotropic Film Growth and Pseudomorphism of Silver on a Germanium (110) Surface

R. Wübbenhorst, K. Hartig, and R. Niedermayer

J. Vac. Sci. Technol. 6, 479 (1969); http://dx.doi.org/10.1116/1.1315660 (1 page)

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Silver has been evaporated on a clean Ge, (110) substrate at various substrate temperatures and evaporation rates, and film growth has been observed by LEED. The first stage of growth is an amorphous absorption layer of Ag atoms. At a definite thickness depending on evaporation parameters anisotropic silver islands are formed which are longer in the (001) direction than in the (110) direction of the substrate. Atomic distances in (110) are in the normal Ag atomic diameters (2.88 Å) while in the (001) direction considerable pseudomorphic strain is observed. The atomic distance in this direction varies from nearly 5.6 Å (the lattice constant of Ge) for very thin films to about 4.08 Å (the lattice constant of Ag) for films of 40 monolayers. The difference in these distances is about three times the maximum error of the measurement. Thus pseudomorphism in this system is clearly shown. Further the dependence of Δa∕a (a=distance of Ag atoms) on the dimensions of the islands in the (001) direction was investigated. The results are in good qualitative agreement with calculations made by Niedermayer concerning the anisotropic growth of islands.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Growth Mechanism of Gold Films Evaporated on Sodium Chloride

K. Mihama

J. Vac. Sci. Technol. 6, 480 (1969); http://dx.doi.org/10.1116/1.1315661 (3 pages) | Cited 2 times

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Various factors influencing the epitaxial temperature are studied by transmission electron microscopy in the initial stages of growth. The particle density at a constant mean thickness is nearly independent of the deposition rate. The electric field applied to the substrate surface brings about the lowering of the epitaxial temperature. The effect is more pronounced by an addition of electron irradiation to the substrate. In accordance with the lowering of the epitaxial temperature, the particle density is increased by the electric field and electron irradiation. From these results, it is concluded that the number of nucleation sites depends on the experimental conditions and that the expitaxial temperature is lower if more sites are present. The results are discussed in terms of Walton’s theory.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Use of Thin Films in Determining the Fundamental Optical Properties of Semiconductors

William Paul

J. Vac. Sci. Technol. 6, 483 (1969); http://dx.doi.org/10.1116/1.1315662 (11 pages)

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The conditions under which measurements of the optical transmission and reflection of epitaxial films at energies well above the fundamental edge can be interpreted to give the bulk spectrum of the complex dielectric constant are discussed. The comparative advantages of film transmission and bulk reflection measurements are assessed. The experimental conditions leading to accurate ϵ̃ (ω) and well-resolved fine structure in the optical spectra from which the electronic band structure may be inferred are described. Illustrations are taken from recent work on the group 4, group 4–6, and group 2–6 semiconductors.
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78.66.-w Optical properties of specific thin films
77.22.Ch Permittivity (dielectric function)

Preparation and Properties of Single-Crystal Lead Telluride Films

G. Gardner Sumner and Lenford L. Reynolds

J. Vac. Sci. Technol. 6, 493 (1969); http://dx.doi.org/10.1116/1.1315663 (5 pages) | Cited 6 times

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Single-crystal PbTe films were prepared on NaCl substrates to examine initial growth and defect structures and to determine the variation in electrical transport properties of 2–5 μ thick films prepared with different deposition parameters. Although these films were uniformly well ordered when deposited on substrates ranging in temperature from 100 to 350°C, widely varying defect distributions were commonly seen during and following film closure. The galvanomagnetic properties of the films were not strongly influenced by deposition parameters. Nearly all the films were n-type as deposited, but conversion to p-type films was accomplished routinely by doping the films with tellurium vapor at 300°–350°C. The lowest carrier concentrations obtained for both n- and p-type films were between 9×1016 and 2×1017∕cm3. These films were incorporated into discrete photosensors to determine detectivity. The maximum value obtained was D∗(λmax,850,1)=2×1010 cmmath∕W at 77 K.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films

Preparation and Properties of Pb1−xLnxTe (Ln=Eu,Yb) Films

R. Suryanarayanan and C. Paparoditis

J. Vac. Sci. Technol. 6, 497 (1969); http://dx.doi.org/10.1116/1.1315664 (1 page) | Cited 2 times

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We have adopted the technique of co-evaporation to prepare Pb1−xLnxTe films. Both amorphous and freshly cleaved NaCl substrates have been used. Structural, optical, and electrical properties of these films were studied. It is found that PbTe–EuTe alloys form single phase solid solutions over the entire range of composition and epitaxial films could be obtained. Electrical and optical properties are reported. n and p-type single-crystal films of PbTe with u77=5000 cm2∕V-sec have been prepared. Transmission and reflection measurements of EuTe films indicate a band gap value of 2.25 eV with an absorption co-efficient of 105 cm−1 in the absorbing region. Electrical measurements of YbTe show it to be a wide band gap material. We also report optical and electrical properties of Pb1−xYbxTe films.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
78.66.-w Optical properties of specific thin films
73.61.-r Electrical properties of specific thin films

Properties of CdxPb1−xS Epitaxial Films

Kepi Wu and J. N. Zemel

J. Vac. Sci. Technol. 6, 497 (1969); http://dx.doi.org/10.1116/1.1315665 (1 page) | Cited 1 time

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We have grown CdxPb1−xS epitaxial films on heated cleaved or polished NaCl substrates using a two source apparatus. The technique is substantially the same as that used by Bis and Zemel for the growth of PbSexTe1−x films. The composition of the films was determined both by the weight loss of the sources and the lattice constant determined by Bragg diffractometry. The films were good single crystals according to Laue patterns obtained on several specimens. The composition range was 0≤×≤0.1. Films were 1.5–6 μ in thickness. The optical transmission and reflection were measured from 2000 Å to 40 μ. There was a systematic increase in the energy of the fundamental absorption edge as x increased. This is in marked contrast to the behavior of SnxPb1−xSe and SnxPb1−xTe where increasing x leads to a decreasing energy gap. Electrical data on films where x is small indicate that the mobility and carrier concentrations are quite reasonable. High resistivities were encountered on materials with x values near to 0.1. Some photosensitivity was observed at room temperature. Values for the index of refraction have also been obtained.
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68.55.-a Thin film structure and morphology
78.66.-w Optical properties of specific thin films
73.61.-r Electrical properties of specific thin films

Acceptor States Due to Defects in Thin Germanium Films

D. J. Dumin

J. Vac. Sci. Technol. 6, 498 (1969); http://dx.doi.org/10.1116/1.1315666 (4 pages) | Cited 5 times

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The electrical characteristics of p- and n-type germanium films grown epitaxially on 1000-Å-thick films of silicon-on-sapphire and spinel have been measured as a function of (a) film thickness, (b) doping density, (c) substrate orientation, and (d) temperature. All of the films were doped to varying extents with acceptors in densities greater than 1015∕cm3 with the acceptor density being varied by controlling the growth parameters. The density of acceptors was correlated with the crystalline perfection of the films, with the more perfect films containing a lower acceptor concentration and having a higher Hall mobility. The defect-acceptors have both a larger scattering cross section and a higher activation energy than does the shallow acceptor, boron. Analysis of the temperature dependent Hall data indicated that the defect-acceptor may actually consist of multiple acceptor levels.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.61.Cw Elemental semiconductors

Study of Quantum Size Effect in Thin Bi Films by Tunnel Spectroscopy

V. N. Lutsky, D. N. Korneev, and M. I. Elinson

J. Vac. Sci. Technol. 6, 501 (1969); http://dx.doi.org/10.1116/1.1315667 (1 page) | Cited 2 times

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We have studied dI∕dV vs V curves of tunnel junctions composed of thin Bi films with silver films as the “bulk” metal. It is known that dI∕dV vs V characteristics of tunnel junctions consisting of a thin film in which the conditions for quantization of the transversal component of quasimomentum are fulfilled and a bulk metal must have a nonmonatomic oscillating character. Some information concerning the energy spectrum for quasiparticles in thin films can be drawn from an investigation of these oscillations. Using a derivative technique enabled us to widen the thickness range of investigated Bi films up to 5000 Å, as compared with 1300 Å at our previous report. Ag and Bi films were evaporated on separate mica substrates. The tunneling carrier was an air gap formed as a result of the film’s and support’s thickness difference when two films were folded together. The structure of the Bi films was a mosaic single crystal with the trigonal axis normal to the film plane. Orientation of crystallites was within 2° or 3°. The average grain size ∼3μ dI∕dV-vs-V curves taken on tunnel junctions composed of a thick Bi film (5000 Å) and a silver film exhibit peaks or a change of slope at voltages of +30, +60, −40, −100 mV (+V corresponds to Bi positive), in good agreement with band edges as observed by Esaki. dI∕dV-vs-V curves taken on junctions with thin Bi films exhibit a fine structure (series of bumps) at positive and negative voltages up to 36 mV; but the above thick film, structure is missing. The changes of position of the bumps and their number under negative bias depends upon the thickness of the Bi film. The values for the electron effective mass component in the trigonal direction and the Fermi energy derived from the spacing between bumps are in good agreement with those known for bulk bismuth. We believe that measuring of a tunneling between two films in quantizing transversal magnetic field would give rise to the sharp peaks of the tunnel current due to the discrete energy spectrum of the carriers.
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73.40.Gk Tunneling

Surface Scattering and Size Effects

R. F. Greene

J. Vac. Sci. Technol. 6, 502 (1969); http://dx.doi.org/10.1116/1.1315668 (1 page) | Cited 5 times

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Size-effect phenomena can provide information about both bulk and surface electronic structure and scattering mechanisms both in normal and superconducting metals, semimetals, and semiconductors. Size effects in transport can arise from any or all of the following: surface mixing of bulk electronic states, surface effects on the electron-electron coupling in superconductors, surface effects on the phonon spectrum, surface scattering. In addition there are subtle surface effects on the transport distribution function, involving the relaxation time approximation, which make the transport theory much more complicated, and less able to give clear information on basic interaction mechanisms. An example of this is the role of electron-electron scattering in the size effect in semimetals. The evidence for extremely strong angular dependence of the surface scattering mechanisms in metals, semimetals, and semiconductors is described.
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72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Tunneling into and through Evaporated Semiconducting Films

I. Giaever and H. R. Zeller

J. Vac. Sci. Technol. 6, 502 (1969); http://dx.doi.org/10.1116/1.1315669 (7 pages) | Cited 5 times

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If two metallic conductors are separated by a sufficiently thin, evaporated, semiconducting film, the observed conduction is mainly due to electron tunneling. We have experimentally demonstrated this fact by using superconducting electrodes. For some of the semiconductors we have used, i.e., CdS and PbS, the tunnel current is sensitive to light, and the resistance of the sample may change by as much as a factor of 1000. The observed resistive change is permanent for all practical purposes if the sample is kept at or below liquid nitrogen temperature. The original resistive state is recovered by cycling the sample to a temperature above 110 K. The energies of the longitudinal optical phonons in the semiconducting films can be obtained from small irregularities in the current-voltage characteristic of the samples; in practice, it is necessary to obtain the first or second derivative of the current-voltage characteristic to see this effect. By altering the samples such that the electrons tunnel into the semiconducting film rather than through the film, the effect caused by the phonons in the current-voltage characteristic is greatly enhanced.
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73.40.Gk Tunneling

Field Emission from Oxidized Metal Films

L. Eckertová

J. Vac. Sci. Technol. 6, 508 (1969); http://dx.doi.org/10.1116/1.1315670 (11 pages) | Cited 2 times

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If a sufficient voltage is applied to a thin-film system of sandwich-type (metal-oxide-metal), an electron emission can be observed under certain conditions. This emission is connected with the presence of a strong electric field within the dielectric and can be considered as a special type of field emission. It is strongly influenced by the properties and the structure of the layers, mainly the dielectric layer and the upper metal layer. The interactions of electrons in these layers are not known exactly enough and the measurement of the mentioned emission properties can considerably contribute to the solution of this problem, In this paper, a survey of the most important experimental data is given—I–V characteristics, temperature dependence, transfer ratio, energy and angular distribution—and a simple theoretical model is proposed, in which the interaction of the traversing electrons with phonons and traps in the dielectric, and with conduction electrons and phonons in the upper metal electrode, is concerned. On the basis of comparison of this theory with experimental evidence, conclusions about the role of single kinds of interactions are drawn.
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79.70.+q Field emission, ionization, evaporation, and desorption

Electrical Breakdown in Thin Dielectric Films

Franco Forlani and Nicola Minnaja

J. Vac. Sci. Technol. 6, 518 (1969); http://dx.doi.org/10.1116/1.1315671 (9 pages) | Cited 21 times

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In this review paper the basic mechanism of electrical breakdown in thin dielectric films is considered; this is still an argument of debate. Some critical points have been identified: it is, for instance, almost generally accepted that the formation of an electron avalanche is the prime agent of the electrical breakdown. Much evidence indicates the role of the cathode material and the increase of the electric strength as the thickness of the dielectric film decreases. It seems to be proved that a dependence upon the thickness according to an exponential law describes quite satisfactorily the results of breakdown measurements. In NaCl single-crystal layers the electric strength is a function of the thickness w proportional to w−1∕2 in the range of the lower thicknesses, but a decrease as w−1∕4 is observed in the range of higher thicknesses. These different exponents are justified by two mechanisms, namely the tunnel injection of electrons from the cathode and the electron-phonon scattering. The analysis of experimental results obtained in polycrystalline Al2O3 and SiO2 layers shows that the dependence as w.−1∕4 holds in the range of lower thicknesses, but for higher thicknesses the electric strength decreases as w−1∕2. This inversion of behaviour can be understood by considering the influence of charged defects in the dielectric film near the cathode. On the other hand it is not possible to conclude that the mechanism of breakdown in thin dielectric films is fully explained, at least when the structural defects play a predominant role.
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77.22.Jp Dielectric breakdown and space-charge effects
77.55.-g Dielectric thin films

Formation of Multiply-Twinned Particles in the Nucleation Stage of Film Growth

Shiro Ogawa and Shozo Ino

J. Vac. Sci. Technol. 6, 527 (1969); http://dx.doi.org/10.1116/1.1315672 (8 pages) | Cited 4 times

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During electron diffraction and electron-microscopic studies on the epitaxy of fcc metals condensed on cleavage face of NaCl crystals by evaporation in ultrahigh vacuum, particles with unusual structures and giving rise to anomalous 111 diffraction spots have been found at early stages of film formation, besides normal particles with orientations such as (001) and (111). Structures of the anomalous particles have been studied in detail chiefly with Au on NaCl, using the dark-field technique. They have been identified as regular pile-ups of twins and so named “multiply-twinned particles.” The following three types of these particles have been observed; the first type is composed of five tetrahedral twins of equal size of which the nucleus tetrahedron has the (111) orientation to the substrate face, the second is composed of 20 tetrahedral twins of equal size of which the nucleus tetrahedron has also the (111) orientation, and the third is composed of five twins of which the nucleus crystal has the (001) orientation. A simple pile-up of twins, however, results in each case in the formation of one or many gaps between twins that have never been observed on electron micrographs. A later study of lattice image revealed that the lattices of the particles are uniformly strained. The existence of multiply-twinned particles of very small size (20–30 Å) suggests that they form already at the nucleation stage. In the anomalous particles atomic distances different from those of the normal lattice occur. With increasing size their structures become unstable owing to the spontaneous straining of the lattices.
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68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.05.J- Electron diffraction and scattering

Orientation Dependence of Nucleation of Iron on NaCl Substrates

S. Shinozaki and H. Sato

J. Vac. Sci. Technol. 6, 534 (1969); http://dx.doi.org/10.1116/1.1315673 (4 pages) | Cited 2 times

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The orientation of epitaxial iron films deposited on cleaved NaCl substrates is known to be determined solely by the nucleation process. Here, an effort is made to select a single orientation out of two dominant orientations, which are well recognized under normal evaporation conditions and have almost identical interfacial energies with respect to the substrate, based on the nucleation theory. The deposition rate of iron has been widely varied by a sublimation technique at fixed substrate temperatures and, at an extremely low deposition rate, the single orientation was found to be selected in accordance with the prediction of the nucleation theory. The effect of water vapor on the epitaxy of iron on rocksalts is reinterpreted in light of this experiment.
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68.55.-a Thin film structure and morphology

Growth of Thin Iron Films on Gold and Rocksalt Substrates at 80 K

E. F. Wassermann and W. Sander

J. Vac. Sci. Technol. 6, 537 (1969); http://dx.doi.org/10.1116/1.1315674 (3 pages) | Cited 1 time

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Gold layers, approximately 1000 Å thick, have been evaporated in ultrahigh vacuum onto air-cleaved rocksalt substrates, held at 80 K. Immediately following the gold evaporation thin iron films have been deposited on top of the gold layers. Part of the iron was also evaporated directly onto the rocksalt. All the layers have been covered with a carbon film at low temperature. Nucleation and growth of the iron layers on top of the Au films have been studied after dissolving the Au quantitatively away. For iron layers of equal thickness the differences in film topology have been investigated. For the same stage of growth these differences can be explained by taking the various binding energies between overgrowth and substrate into account. The results can be used to explain relations between the evaporation sequence and changes in the critical temperature of superconductor-normal metal packages in the proximity effect.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Gold Satellite Clusters on Muscovite Mica

W. L. Morris and R. L. Hines

J. Vac. Sci. Technol. 6, 539 (1969); http://dx.doi.org/10.1116/1.1315675 (4 pages) | Cited 1 time

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Groups of gold clusters consisting of a large main cluster and smaller satellite clusters within a few tens of angstroms of the main cluster are nucleated from vapor on the cleavage face of muscovite mica in ultra-high vacuum. The satellites are seen for low cluster nucleation densities for which the random occurrence of such close cluster formations is extremely unlikely. The dependence of the average frequency of satellite occurrence per cluster upon substrate temperature and gold flux is examined. In addition, the relationship between the frequency of satellite observation and the diameters of the clusters with satellites is studied for fixed evaporation conditions. The satellites are tentatively interpreted as resulting from cluster nucleation on gold atom pairs which have escaped from established parent clusters.
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68.55.-a Thin film structure and morphology

Effect of Oxygen on the Formation of Germanium Films

Robert F. Adamsky, Klaus H. Behrndt, and William T. Brogan

J. Vac. Sci. Technol. 6, 542 (1969); http://dx.doi.org/10.1116/1.1315676 (4 pages) | Cited 3 times

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The influence of background oxygen pressure at levels between 10−10 and 10−6 Torr on the crystallographic order of Ge films evaporated on (111) Ge was investigated. The substrates were chemically cleaned and∕or subjected to thermal in situ cleaning. Oxygen partial pressures as low as ∼5×10−9 Torr were found to increase the epitaxial temperature by 50–75° C, and the amorphous-polycrystalline transition by 125°–150° C for substrate temperatures in the range 150–310° C. At partial pressures of ∼5×10−8 Torr, the oxygen effect increases with decreasing substrate temperature and increasing deposition rate, while preannealing of the substrates at 600° C eliminates subsequent oxygen effects. The observations are interpreted in terms of oxide formation; they offer an explanation for the appreciable decrease in epitaxial temperature for films deposited in UHV compared to conventional vacua.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

GaAs, GaP, and GaAsxP1−x Epitaxial Films Grown by Molecular Beam Deposition

J. R. Arthur and J. J. LePore

J. Vac. Sci. Technol. 6, 545 (1969); http://dx.doi.org/10.1116/1.1315677 (4 pages) | Cited 27 times

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Epitaxial films of GaAs, GaP, and GaAsxP1−x were grown on GaAs and GaP in ultrahigh vacuum from molecular beams of Ga, As2, and P2. Reflection electron diffraction patterns indicated the films were epitaxial on GaAs as low as 700 K and on GaP at 870–900 K. At lower temperatures, twinning became excessive. In films of GaAsxP1−x, the ratio As∕P was four times the ratio of As2flux∕P2 flux incident on the substrate. If the rate-controlling step were solely the reaction of adsorbed Ga with the impinging As2 or P2, the ratios should have been equal; the discrepancy apparently was due to rapid desorption of P from the surface.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors

Nucleation and Epitaxial Growth of Chemically Formed Sulphide and Oxide Films

G. Hecht, J. Herberger, and Ch. Weissmantel

J. Vac. Sci. Technol. 6, 548 (1969); http://dx.doi.org/10.1116/1.1315678 (1 page)

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In previous investigations the kinetics of the reactions between oriented Cd- and Zn-films and pure sulphur and oxygen vapor, respectively, was studied. The sulphur or oxygen uptake followed a two-step time law: after a fast logarithmic part the curves show a much slower reaction, which can be described by the function a=ct1∕n (a—amount of sulphur or oxygen uptake, t—time) where the parameters c and n are dependent on temperature and film structure. The mechanism of the film growth has been studied now by detailed structure investigations including x-ray and electron diffraction methods, and x-ray microanalysis. So far the following systems were studied: (1) Highly texturized Cd- and Zn-films on glass substrates treated with sulphur vapor and oxygen, respectively, at about 10−1 Torr at temperatures between 20° and 250° C and reaction times on the range from 1 to 104 min and (2) single-crystalline disks of Cd treated with sulphur vapor under the conditions mentioned above. The main results are: (1) a very thin (about 50 Å) and nonoriented surface film is formed within 1 min of contact between the gas and the clean metal surface. (2) In the second step sulphide and oxide nuclei of diameters between 102 and 103math were grown until the whole crystal surface was covered with nuclei. The preferential growth direction is perpendicular to the 0001 surfaces of the hexagonal, metal crystals. The nucleation rate depends strongly on the plane orientation and the density of defects and impurities. (3) The slow reaction after the coverage with nuclei leads to the coalescence of the nuclei and recrystallization of the grown layer. A slow, thickness growth can be described by field transport of metal ions through the layer. Under certain conditions it is possible to prepare epitaxial films with relative large single-crystalline regions. Theoretical interpretation of the results leads to the consequence, that the quantitative description of formation of thin surface films on metals according to the models of Cabrera, Mott, and Hauffe must be modified because nucleation and recrystallization processes have an important influence on the kinetics in the early reaction steps. A treatment on the basis of random-walk-theory gives a satisfying description of the whole growth process. Furthermore, it looks promising that highly-oriented and single-crystalline films for special electronic applications may be grown by this method.
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68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth

The Nature of Surface States on III–V and II–VI Semiconductors

Jules D. Levine

J. Vac. Sci. Technol. 6, 549 (1969); http://dx.doi.org/10.1116/1.1315679 (3 pages) | Cited 4 times

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Surface state experimental data is shown to agree with recent theories developed for the large bandgap ionic and partially ionic crystals. The surface states appear in pairs. An acceptor-like surface state band lies generally a few tenths of an eV below the conduction band, and a donor-like surface state band generally lies a few tenths of an eV above the valence band. The surface state bands merge with the corresponding conduction and valence bands. The smaller the bandgap Eg of the compound, the closer the states move towards midgap, provided Eg>1 eV. Furthermore, for n-type samples the bands bend up at the surface, while for p-type samples the bands bend down. But for Eg<1 eV, the surface Fermi level is always located at or near the valence band edge; this may be because these crystals are less ionic.
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73.20.At Surface states, band structure, electron density of states

Magnetoresistance, Hall Effect, Conductivity, and Mobility in Polycrystalline CdSe Films

G. Jäniche and H. Berger

J. Vac. Sci. Technol. 6, 552 (1969); http://dx.doi.org/10.1116/1.1315680 (4 pages) | Cited 2 times

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Conductivity, Hall effect, and transverse magnetoresistance were measured on evaporated polycrystalline CdSe films between 80 and 700 K. The mobility calculated from magnetoresistance is different in magnitude and temperature dependence from that calculated from conductivity and Hall effect, since the latter one is not only determined by the scattering mechanisms but also by the numbers and properties of potential barriers at crystallite boundaries. The analysis of magnetoresistance shows that at low temperatures the electron mobility is controlled by impurity scattering and at high temperatures by optical phonon scattering. Scattering by ionized impurities considerably influences the mobility at room temperature.
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73.61.Ga II-VI semiconductors
73.50.-h Electronic transport phenomena in thin films
72.10.-d Theory of electronic transport; scattering mechanisms

Acoustic Properties and Crystallographic Structure of CdS Double-Layer Acousto-Electric Transducers

W. Duncan, R. H. Hutchins, and P. A. M. Stewart

J. Vac. Sci. Technol. 6, 555 (1969); http://dx.doi.org/10.1116/1.1315681 (4 pages) | Cited 1 time

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Acoustic properties and crystallographic structure of cadmium sulphide, evaporated, double-layer transducers have been investigated. The double-layer structure consists of a relatively thick, 5–20 μ, highly conducting base layer, within which the required c-axis orientation is developed. A thin 0.1–1.0 μ high resistivity film, which determines the fundamental frequency response of the transducer, is deposited on the highly conducting layer. The c-axis orientation of this top layer is determined by that of the conducting layer; the resonant mode being determined by the angle of inclination of the c-axis to the substrate normal. Operation of these transducers in the frequency range 1–3 GHz has been investigated in both modes. Tuned conversion efficiencies of less than 10dB have been observed. Crystallographic studies have been carried out in an attempt to correlate the film structure with acoustic properties. Results will also be presented on the efficiency of this technique in producing efficient acousto-electric transducers for higher microwave frequencies. The top layers of these transducers can be formed by either direct evaporation or epitaxial growth and the performance of both types has been studied.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Transport Properties of Thin Films of SnTe

Yusuke Ota and J. N. Zemel

J. Vac. Sci. Technol. 6, 558 (1969); http://dx.doi.org/10.1116/1.1315682 (4 pages) | Cited 3 times

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Epitaxic films of SnTe have been grown on heated NaCl substrates using extremely well controlled source and substrate heaters. As a result, systematic studies were carried out on the effect of evaporation time on the film properties. Without adequate preevaporation, nonuniform films are grown with carrier concentration decaying exponentially from the SnTe-NaCl interface on out. These films show interesting electrical properties. In the thinnest films grown (∼400 Å), the mean free path was somewhat greater than the film half thickness. The mobilities at room temperature and 77 K were in excellent agreement with bulk data. Because of these data, it is concluded that the scattering at the surface is largely specular. Optical data partially confirm the conclusions on the presence of large inhomogeneities.
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73.61.Le Other inorganic semiconductors
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Electrical and Optical Properties of Amorphous vs Crystalline GeTe Films

S. K. Bahl and K. L. Chopra

J. Vac. Sci. Technol. 6, 561 (1969); http://dx.doi.org/10.1116/1.1315683 (5 pages) | Cited 4 times

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Ac and dc conductivity, tunneling, and optical transmission and reflectance studies have been made on amorphous and crystalline (rhombohedral and NaCl) GeTe films (80 Å to 10 μ thick) prepared by evaporation and by sputtering. The crystalline films behave like a p-type degenerate semiconductor with Fermi level ∼0.3–0.5 eV in the valence band, resistivity ∼10−4Ω cm, carrier concentration ∼1020 to 1021∕cm3, Hall mobility ∼25–120 cm2∕V sec, and a small, positive (metallic) temperature coefficient of resistivity. Amorphous films show a high resistivity which increases exponentially from ∼103 to >1010 Ω cm as the temperature decreases from 300–77 K, corresponding to an activation energy of 0.3–0.4 eV. The ac conductivity increases as ωn(n<1) to approach a constant value above ω=90 kc. Simultaneously, the activation energy for conduction decreases continuously to a nearly zero value. The conductivity also increases rapidly as a high power of the electric field at >104 V∕ cm. The near infrared indices of amorphous and crystalline structures are 4.0 and 5.6, respectively. The optical absorption edge is nearly the same (∼0.8 eV) for the crystalline and amorphous films. A tentative explanation of the transport behavior of amorphous films is possible in terms of conduction by two parallel mechanisms: (a) in the conduction band by intrinsically excited carriers, and (b) by a hopping process in the trap-like localized levels above the Fermi level in the valence band.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
73.40.Gk Tunneling

Investigations of Scattering and Trapping Processes of Carriers in Ultrapure Germanium Films

A. V. Rzhanov, W. P. Migal, and N. N. Migal

J. Vac. Sci. Technol. 6, 566 (1969); http://dx.doi.org/10.1116/1.1315684 (3 pages) | Cited 2 times

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Films of about 100 μ thickness were grown by iodide-transport process in a closed tube, with the concentration of acceptor impurities below 1012 cm−3. Measurements were made on the samples, which had one natural surface of film growth and the other surface prepared by the usual polishing and etching procedure. The Hall coefficient and surface-conductivity measurements were made by a dc field-effect method in a temperature range between 100 and 300 K. Results of the measurements are expressed in terms of surface mobility and trapped charge curves. The scattering of electrons is a diffuse process for both conditions of the surface (natural-grown surface and treated surface of the film) and over the whole temperature range. The scattering of holes is diffuse on the treated surface and only partially diffuse on the natural surface of film. The probability of diffuse reflection for holes in this case is equal to 0.3–0.4 and does not depend on temperature. The dominant mechanism of the surface scattering is discussed for different cases. The trapped charge curves for both conditions of the surface correspond to the assumption of a continuous spectrum of surface states. The form of the spectrum is independent of temperature for the natural surface. For the treated surface it changes with temperature, owing to an adsorption process.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Cw Elemental semiconductors

Theory and Practice of Steady-State Evaporation of Alloys

E. Brock Dale

J. Vac. Sci. Technol. 6, 568 (1969); http://dx.doi.org/10.1116/1.1315685 (5 pages) | Cited 1 time

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InSb films have been grown by steady-state evaporation, a technique that produces a vapor with the same composition as the starting liquid. Films deposited on glass substrates at room temperature typically have Hall coefficients of 10–50 cm3∕C, resistivities of 0.05 and 0.5 Ω cm, and Hall mobilities of the order of 200 cm2∕V sec. X-Ray fluorescence analyses of films deposited on thin plastic substrates at room temperature indicate random departure from stoichiometry of as much as 1%. Comments are made on source design and conditions that may cause deviations from stoichiometry. The theory of steady-state evaporation is briefly discussed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.61.Ey III-V semiconductors
68.55.Nq Composition and phase identification

Transport Properties of Electrons in Inverted InSb Surface

K. F. Komatsubara, Y. Katayama, N. Kotera, and T. Kobayashi

J. Vac. Sci. Technol. 6, 572 (1969); http://dx.doi.org/10.1116/1.1315686 (4 pages) | Cited 1 time

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Measurements were made of electrical transport properties of the electrons in inversion layers produced in metal–oxide–p-InSb structure at 4.2 K. One possible interpretation is reported. Surface conductance Δσs due to inversion layers as a function of gate voltage VG was measured in magnetic field H up to 14 kOe. The curves of Δσs in the magnetic field normal to the surface had plateaus. The width of the plateaus were enlarged on the positive side of VG with increasing magnetic field. While Δσs in the magnetic field normal to the surface decreased ordinarily with increasing H, Δσs in the field parallel to the surface plane tended to a finite value. Values of Δσs showed two peaks when the direction of the magnetic field was rotated in a plane normal to the surface current. The width of the peak was narrower in the case of magnetic fields where electrons were pushed toward the oxide–InSb interface rather than into the bulk of the InSb. These characteristics may be interpreted as follows: The effect of quantization of electron motion in the inversion layer becomes clearer in the behavior of Δσs with the aid of a magnetic field which quantizes the motion of electrons in planes parallel to surface. The peculiar dependence of Δσs on the direction of the magnetic field is thought to originate in the different mechanisms of electron scattering on both sides of the inversion layers mentioned above.
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73.25.+i Surface conductivity and carrier phenomena
72.80.Ey III-V and II-VI semiconductors

Numerical Solutions of a Field Effect Model for Indium Antimonide

R. H. Hartley

J. Vac. Sci. Technol. 6, 575 (1969); http://dx.doi.org/10.1116/1.1315687 (1 page)

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Numerical solutions of a field effect model for indium antimonide are presented. Solutions of a model using Boltzman statistics are compared with those using Fermi–Dirac statistics. A similar comparison of results is made between models employing a parabolic conduction band and non-parabolic band as described by Kane. For the model employing Fermi–Dirac statistics and the Kane band structure, surface conductance and Hall effect are calculated specular and diffuse surface scattering. For accumulation layers, the space charge region is first replaced by a “square-well” potential of width an Effect Debye Length while for depletion layers the potential barrier is treated as a specular reflector. Surface mobilities, field effect mobilities, and Hall effect data are computed for comparison, with experimental field effect measurements made on polycrystalline, vacuum deposited InSb films having field effect mobilities of up to 0.2 m2∕V sec, and bulk mobilities of up to 2 m2∕V sec. The “square-well” potential approximation is improved by inserting the actual shape of the space charge region for both electrons and holes. Finally, the variation of electron mobility with energy in the conduction band is accounted for by including the appropriately averaged effective masses in the computation.
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72.20.-i Conductivity phenomena in semiconductors and insulators
73.25.+i Surface conductivity and carrier phenomena
72.80.Ey III-V and II-VI semiconductors

Studies of Epitaxial Growth of Metallic and Nonmetallic Films by Means of High-Resolution Ciné and Still-Electron Microscopy

Goro Honjo and Katsumichi Yagi

J. Vac. Sci. Technol. 6, 576 (1969); http://dx.doi.org/10.1116/1.1315688 (7 pages) | Cited 11 times

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Growth processes of metallic vacuum deposits, Ag and Au, and nonmetallic deposits, PbS and PbSe, on MgO and MoS2 substrates have been studied by means of direct ciné recording of electron micrographs resolvable down to 17 Å moiré spacing. The detailed kinetics of the film growth as revealed by the moiré fringes are discussed in the light of growth mechanisms. The main differences between the metallic and nonmetallic film growths are the absence, in the cases of nonmetallic film growth, of “liquid-like” behavior during coalescence, and lack of the secondary nucleation, which are known to be very important in metallic film growth. Growth processes of so-called multiply-twinned particles and twin formation and release in the metallic film growth have also been studied. The direct observation of formation of pseudomorphic interfacial dislocations was carried out in the case of PbSe on PbS. The lattice spacing anomalies in pseudomorphic overgrowth have been examined by means of high-resolution still-electron microscopy. Moiré spacing analysis showed a slight anomaly in the case of Au and MoS2. The problem in the observation of the lattice image to measure lattice distortion is discussed.
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68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Electron Microscope Study of Ge–(GaxIn1−x)As Interfaces

G. O. Krause

J. Vac. Sci. Technol. 6, 582 (1969); http://dx.doi.org/10.1116/1.1315689 (4 pages) | Cited 1 time

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Accommodation of lattice mismatch across Ge–(GaxIn1−x)As interfaces has been investigated. Single crystalline alloy films of different composition were prepared by flash evaporation on epitaxial {111} Ge substrates. The specimens contained only few twin boundaries as revealed by n∕3〈224〉 reflections. Sufficiently large uniform areas were available for studying the heterojunction properties. Dark-field micrographs exhibit periodic contrast lines parallel to 〈112〉 directions. Measurements of line spacings for different alloy compositions confirm an interpretation with misfit dislocations at the heterojunctions. Evidence for partial mismatch accommodation was obtained. Estimated values for strain relief and its dependency on misfit agree qualitatively with predictions based on the van der Merwe theory.
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68.35.Ct Interface structure and roughness
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Misfit Dislocations in the Bicrystal System of Silicon-Boron-Doped Silicon

Yoshimitsu Sugita, Masao Tamura, and Katsuro Sugawara

J. Vac. Sci. Technol. 6, 585 (1969); http://dx.doi.org/10.1116/1.1315690 (4 pages) | Cited 5 times

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Arrangement of atoms at the interface of a bicrystal system with small lattice parameter differences has been investigated through the observation of the creation of misfit or interfacial dislocations. Specimens were prepared by epitaxial deposition of pure-silicon films onto boron-doped silicon substrates. The conditions required to create misfit dislocations were investigated as a function of the film thickness for both cases of thin and thick substrates. The well-defined critical film thickness was found, and smaller values were found for the thick substrate specimens. Results are interpreted in terms of the van der Merwe theory. Effect of heat treatment upon the misfit dislocation distribution was examined. It was observed that dislocations reacted to form networks in a complicated manner. The dislocation climb rate was negligibly small compared to the diffusion length of boron impurity.
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68.35.Ct Interface structure and roughness
61.72.Lk Linear defects: dislocations, disclinations

Epitaxial Growth of Titanium Thin Films

Franklin E. Wawner and Kenneth R. Lawless

J. Vac. Sci. Technol. 6, 588 (1969); http://dx.doi.org/10.1116/1.1315691 (3 pages) | Cited 7 times

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Single crystal thin films of titanium have been epitaxially grown on NaCl substrates of three different orientations [(001), (110), (111)]. At thicknesses above 500 Å, the normal hexagonal close-packed structure is obtained. Below approximately 350 Å, the metal is seen to grow in a previously unreported face-centered cubic structure with the lattice parameter, ao=4.33 math. This structure is thought to result from pseudomorphic type growth on the NaCl substrate in keeping with proposed misfit theories. At a critical thickness (∼200–300 Å), there is a transformation from the fcc phase to the normal hcp phase in deposits on the (001) and (111) substrate surfaces. The deposit on the (110) NaCl surface demonstrated a coexistence of fcc and hcp material at all thicknesses.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Epitaxial Growth of Sb2Te3 Films

L. H. Gadgil and A. Goswami

J. Vac. Sci. Technol. 6, 591 (1969); http://dx.doi.org/10.1116/1.1315692 (3 pages) | Cited 5 times

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An electron diffraction study has been made of vacuum deposited Sb2Te3 on (100) and (111) faces of rocksalt as well as on (0001) face of mica at substrate temperatures varying from room temperature to about 350° C. The deposits developed two-degree orientations generally above 100° C. On a (100) face of rocksalt the deposits grew with 2-d {30.4} (both normal and anti) orientations along with {00.1}, but the crystallites with the latter orientation were rotated by 30°. At higher temperature only the former orientations were predominant. On the other faces only {00.1} orientation was observed, though on a mica substrate, the crystallites were rotated by 30°. In all cases Sb2Te3 retained its normal rhombohedral structure.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Preparation and Structural Properties of GaN Thin Films

B. B. Kosicki and D. Kahng

J. Vac. Sci. Technol. 6, 593 (1969); http://dx.doi.org/10.1116/1.1315693 (4 pages) | Cited 20 times

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We describe here a method that is capable of producing GaN thin films on either heated or unheated substrates. This method makes use of a remote gaseous discharge to dissociate molecular N2 into atomic N, which is then able to combine with Ga being evaporated onto the substrate. Using glancing angle x-ray diffraction and reflection electron diffraction techniques, we have studied structural properties of GaN thin films grown with this system on substrates of fused quartz, and oriented GaAs and Al2O3. At low substrate temperatures, smooth, transparent polycrystalline films result, while at temperatures above 550° C we have obtained epitaxial GaN on both {111} faces of GaAs and on {0001} faces of Al2O3. The epitaxial films show a simple orientational relationship to these substrates.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Some Aspects of Structure Sensitive Properties of Semiconductor-Insulator Interface Systems

A. G. Revesz

J. Vac. Sci. Technol. 6, 596 (1969); http://dx.doi.org/10.1116/1.1315694 (1 page)

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In semiconductor-insulator interface systems the method of preparing the insulating film, including after-treatments, greatly affects the structure of the film and interface. This is manifested in the charge distribution which can be measured with the very sensitive surface impedance method. In addition, electron irradiation can be used as a diagnostic method to reveal defects that can capture electrons or holes. Coupled with EPR absorption measurements, electron irradiation of Si–SiO2 structures showed that (1) paramagnetic centers form mainly at the interface; (2) these centers differ from K-centers produced in bulk Si by electron irradiation; (3) paramagnetic centers were found after the removal of the oxide film except for those specimens which were annealed in He after oxidation; (4) the presence of hydrogen (or hydroxyl) in the SiO2 film and∕or at the interface leads to various phenomena, such as, increased radiation resistance and increased influence of high electric field at elevated temperature. Incorporation of Al during thermal oxidation of Si gradually decreases the effect of electron irradiation. When the Al∕Si ratio in the oxide is 0.1, the radiation induced oxide charge is comparable to that of Si–Al2O3 structures, even though the “bulk” properties of the film are essentially identical with those of pure SiO2. The Al2O3 films, prepared by thermal decomposition of Al-butoxide, are generally less sensitive to electron irradiation than SiO2 films grown in dry oxygen: under identical conditions the introduced positive electronic charge is about 3×1012 cm−2 as against ∼2×1013 cm−2. If a thin (∼200 Å) SiO2 film is present between the Si and Al2O3, then electron irradiation reveals that the original charge distribution is metastable: the positive charge at the Si-SiO2 interface is replaced by negative charges from the Al2O3 film, but this is (partially) compensated by positive charge generated by irradiation. The metastable charge distribution in Si–SiO2–Al2O3 structures apparently cannot be stabilized by heat treatment alone, the application of an electric field and∕or electron irradiation is necessary.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
73.20.-r Electron states at surfaces and interfaces

Dielectric Behavior and Structural Changes in Alkali Halide Films

C. Weaver and S. Lorenzoni

J. Vac. Sci. Technol. 6, 597 (1969); http://dx.doi.org/10.1116/1.1315695 (4 pages)

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Alkali halide films deposited at room temperature generally show two dielectric loss mechanisms. A low-frequency peak which usually appears well below 1 Hz at room temperature is produced by blocking of charge-carriers at the electrodes. A second loss peak, which is usually two or more decades higher in frequency, has been attributed to blocking of charge-carriers at intercrystalline boundaries. To observe the corresponding behavior of films deposited at low temperatures, it is necessary to choose a material with a fairly high cation mobility such as LiBr or LiI. Measurements on LiBr films deposited at liquid-nitrogen-temperature show only a single loss peak, which moves towards higher frequencies as the temperature increases and is due to blocking of charge-carriers at the electrodes. There is no evidence of blocking at intercrystalline boundaries, until the films have been annealed at room temperature for 24 h. When the measurements are repeated after annealing, the original loss peak is replaced by two separate loss peaks, of which the high-frequency peak (with an activation energy of 0.4 eV) is due to blocking at intercrystalline boundaries, while the low-frequency peak has an activation energy of 0.2 eV, well below the activation energy of 0.39 eV associated with normal cation vacancy migration. The results are explained in terms of the development of charged surface layers on the crystallites during annealing (Frenkel–Lehovec effect) combined with crazing or cracking of the film due to the extreme temperature range, which results in surface migration along the crazing boundaries with a corresponding activation energy.
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77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
68.55.-a Thin film structure and morphology

AC Impedance of Space-Charge Barriers

J. Maserjian

J. Vac. Sci. Technol. 6, 600 (1969); http://dx.doi.org/10.1116/1.1315696 (1 page)

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The ac impedance has been considered in a general way which includes the effect of a distribution of trapping states within Schottky-type energy barriers. Starting with the complete unipolar transport equation, and introducing a density-of-trapping-states function, depending generally on both position and energy, one arrives at a useful result. This is possible because of the rapid variation of trapping relaxation times with position in such barriers, which tends to restrict their main contribution to a narrow range of positions and energies. Thus, a relatively simple expression is obtained which relates the trap density to ac impedance measurements, at regions of the barrier corresponding to the applied frequency, voltage, and temperature. With these three independent variables, one can experimentally scan a sizable portion of the barrier, obtaining a profile of trap densities and other barrier properties as well as independent tests on the self-consistency of the method. Some experimental results obtained from thin-film capacitors are used to illustrate the method. These also serve to indicate the existence of a large ionic space charge in these barriers which we have reason to believe is a common characteristic of many thin insulator films.
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73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Jp Dielectric breakdown and space-charge effects
77.55.-g Dielectric thin films

Application of the Gevers–Du Pre Theory of Amorphous Dielectrics

William Isler and Lester Kitchman

J. Vac. Sci. Technol. 6, 601 (1969); http://dx.doi.org/10.1116/1.1315697 (1 page)

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A review is given of the Gevers–du Pre theory of amorphous dielectrics and its findings are examined for applicability to amorphous films of silicon monoxide (SiO). In the context of the theory amorphous dielectrics are defined as those insulators having irregular structures, a wide range of activation energies, and a broad spectrum of relaxation times. Inasmuch as polycrystalline film dielectrics display a distribution of relaxation times, the Gevers–du Pre theory should apply to films of SiO and many other dielectrics. For the present study, SiO was deposited onto boro-silicate glass substrates at rates ranging from 54 to 133 Å∕min. The values of the temperature coefficient of capacitance (TCC) showed a strong dependence upon the deposition rate, varying from −23 to +300 ppm∕°C. The negative values were obtained for the slower deposition rates, and the positive values for the faster rates. All of the TCC data agreed qualitatively with the Gevers–du Pre theory, suggesting that the negative TCC’s are due to large expansion coefficients and small film densities obtained at slow deposition rates. The results of the present study also suggest that zero TCC’s can be obtained for SiO films by precise control of the deposition rate.
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77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Electrode Effects on Bistable Switching and Dielectric Breakdown of Nb2O5 Diodes

T. W. Hickmott

J. Vac. Sci. Technol. 6, 601 (1969); http://dx.doi.org/10.1116/1.1315698 (1 page)

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The insulating character of thin oxide films can be destroyed by the formation of a voltage-controlled negative resistance characteristic, a current-controlled negative resistance characteristic, or by destructive dielectric breakdown. Nb–Nb2O5-metal diodes, after voltage breakdown, exhibit current-controlled negative resistance and switching between two stable conduction states. The initial conductivity, switching properties, memory effect, and destructive dielectric breakdown of Nb–Nb2O5-metal diodes depend on the counterelectrode metal. Before breakdown, hole injection at the Nb2O5–Au interface plays a significant role in determining electronic conduction, rectification, and electroluminescence of Nb–Nb2O5–Au diodes with oxide thickness between 50 Å and 3600 Å. Bistable switching and dielectric breakdown of Nb–Nb2O5–Au diodes occur at small conducting filaments which form when high voltage is applied to the diode. Electro-luminescence of Nb–Nb2O5–Au diodes after establishment of switching indicates that hole injection occurs at the Nb–Nb2O5–Au interface, just as is the case for diodes before breakdown. Visual observation shows the destructive dielectric breakdown in Nb–Nb2O5–Au diodes differs markedly from destructive breakdown in Nb–Nb2O5–Cu diodes. If low work function metals such as In, Zn, or Pb are used as counterelectrodes, Nb–Nb2O5-metal diodes are initially non-rectifying. After breakdown they exhibit switching characteristics and memory effects that differ from Au or Cu diodes.
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73.40.Rw Metal-insulator-metal structures
77.22.Jp Dielectric breakdown and space-charge effects
77.55.-g Dielectric thin films

Interpretation of Destructive Breakdown in Thin Dielectric Films

Paul P. Budenstein and Paul J. Hayes

J. Vac. Sci. Technol. 6, 602 (1969); http://dx.doi.org/10.1116/1.1315699 (3 pages) | Cited 3 times

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Klein and Gafni have phenomenologically classified breakdown in thin-film capacitors as “single hole,” “propagating,” and “maximum voltage.” Maximum-voltage breakdown, which is supposed to yield the ultimate dielectric strength of the bulk dielectric, is here investigated by adding to the test circuit of Klein and Gafni, a silicon-controlled rectifier that removes the applied voltage within a few microseconds of the occurrence of breakdown. It is shown that maximum-voltage breakdown is initiated as a single-hole breakdown and that total destruction occurs through a series of consecutive breakdowns, each of which is localized and similar to other single-hole breakdowns. The negative resistance region that precedes maximum-voltage breakdown is believed incidental, not causative.
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77.22.Jp Dielectric breakdown and space-charge effects
77.55.-g Dielectric thin films

A New Method for Doping of Thin Insulating Films and the Comparison between the Electrical Characteristics of Undoped and Doped Films

J. Antula

J. Vac. Sci. Technol. 6, 605 (1969); http://dx.doi.org/10.1116/1.1315700 (1 page) | Cited 1 time

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A new method for post-deposition treatment of thin insulating films is described. This method allows the doping of evaporated thin insulating films or thin oxide films manufactured by thermal or electrolytical oxidation, glow discharge process, etc. It is possible to dope the thin insulating films with one or more substances and to control the procedure for each substance independently. Experimental work has been done applying this method to Al2O3 films. The range of film thicknesses was approximately 30–1000 Å. The impurities we used were Cd, Cu, Ag, Au, and Zn or the combination of two materials. To compare the electrical characteristics of doped and undoped films, only one part of an insulating film was doped, the other part remained undoped. In addition the electrical dc conductivity and electrical capacitance of both film parts was measured. The characteristics obtained show a possible increase in conductivity of doped films of two orders of magnitude or more. The current transport mechanism involved and the influence of doping on various physical parameters was discussed.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.55.-g Dielectric thin films
73.61.Ng Insulators

Growth Mechanism and Some Physical Properties of Silicon Nitride Thin Films Prepared by Reactive Sputtering in Nitrogen

J. Cervenǎk, L. N. Aleksandrov, R. N. Lovjagin, and E. A. Krivorotov

J. Vac. Sci. Technol. 6, 605 (1969); http://dx.doi.org/10.1116/1.1315701 (1 page)

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It is shown that the growth of Si3N4 thin films on single-crystalline Si substrates can be characterized by a formation of two-dimensional nuclei with a successive growth into a continuous amorphous thin film. Such films are distinguished by a break-through voltage 2–7×106 V∕ cm, di-electric constant 5–7 and index of refraction 2. Infrared spectra of absorption show the presence of complexes Si3N4 only. Electronmicroscopic investigations of the surface of single-crystalline Si samples allowed to ascertain the effect of the surface layer structure (single-crystalline with Kikuchi lines, amorphous and polycrystalline) upon the surface-state concentration for the interface Si–Si3N4. Beside a chemical treatment with the surface of the single-crystalline Si substrates, we used a special mechanical polishing giving single-crystalline surfaces with Kikuchi lines. The concentration of surface states on structures Si–Si3N4–Al determined from measurements of C=f∕V∕ characteristics lay in the interval 1010–1012 cm−2. We observed that the form of the hysteresis curve C=f∕V∕ depended on the rate of switching on the voltage on the sample. This dependence was diminished or even removed by heating the Si substrate to temperatures more than 500°C, in vacuum 10−6 Torr.
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81.15.Cd Deposition by sputtering
77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects
73.20.At Surface states, band structure, electron density of states

Internal Stresses

W. Buckel

J. Vac. Sci. Technol. 6, 606 (1969); http://dx.doi.org/10.1116/1.1315702 (4 pages) | Cited 23 times

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Vacuum-deposited films generally exhibit remarkable internal stresses. The various attempts to explain the origin of these stresses, especially of those produced during the condensation will be discussed. Based on the “Step Rule” for crystal growth (Ostwald, 1897) a new model will be proposed. Its applicability will be demonstrated by discussing results for gallium, bismuth, and several other materials. This model yields an interpretation for the stress-free growing of amorphous films as well as for the occurrence of compressive stresses under special conditions and for special materials.
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68.60.Bs Mechanical and acoustical properties
81.15.Aa Theory and models of film growth

Ageing Processes in Thin Films

L. S. Palatnik

J. Vac. Sci. Technol. 6, 610 (1969); http://dx.doi.org/10.1116/1.1315703 (1 page)

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The paper presents a review of the results obtained by the author and his co-workers. “Natural” and “artificial” ageing result in a wide range of phenomena with the former occurring at room temperature and the latter at elevated temperatures. Ageing times can range from a fraction of a second to several seconds. The following types of natural and artificial ageing are observed in thin films: (a) Phase processes of ageing—These phenomena consist of changes of the composition and structure of non-equilibrium phases, i.e., evtectoid decomposition, decomposition of super-saturated solutions, of intermetallic and chemical compounds, etc. Ordering and disordering of phases, oxidation and other slow chemical processes are also considered here. (b) Structural processes of ageing—This group of phenomena comprises structural transformations without changes of chemical composition, namely, martensitic transformations, recrystallization, texture formation in polycrystals, sperolite formation in amorphous (glassy) phases, formation and relaxation of macrostresses (I. kind), etc. (c) Substructural processes of ageing—Substructure transformations by diffusion without any changes of the chemical composition and of the symmetry of the crystal lattice are considered, such as relaxation processes, polygonization, changes of the concentration of cystallographic defects (vacancies, dislocations, etc.), or of the dispersion and orientation of crystallites as well as of the values of oriented and disordered microstresses and microdeformations. All these processes, resulting from natural and artificial ageing, were studied by electron microscopy and diffraction as well as x-ray diffractometry and the measurement of structure sensitive properties (mechanical, electrical, magnetic, semiconducting, etc.). These ageing processes were often found to proceed in many stages in accordance with Ostwald’s rule of steps. This was especially true for substructure ageing.
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68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology

Stress and Structure in Thin Metal Films

T. N. Rhodin and P. W. Palmberg

J. Vac. Sci. Technol. 6, 611 (1969); http://dx.doi.org/10.1116/1.1315704 (1 page)

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It has long been recognized that the stress and crystallographic structure of extremely thin metal films corresponding to several monolayers or less on metal substrates may be uniquely different from that of the equivalent orientation in the bulk metal. The overlayer may consist of the same metal, of a second metal with a related lattice-parameter, or of a different metal not characterized by a closely related lattice parameter. The formation of “superstructures” during early growth stages of fcc metals for these various typical cases will be discussed in terms of the analysis of low energy electron diffraction patterns associated with the occurrence of two-dimensional super-lattices. Theoretical calculations of the dependence of surface structure on lattice strain will also be discussed in terms of conditions for superstructure formation and shown to be in good agreement with the predictions of Frank and van der Merwe. For example, multiple diffraction analysis of LEED patterns for very thin overlayers of gold on Pd(100) surfaces indicate that since the critical misfit between the Pd-substrate and Au-overlayer is not exceeded, pseudomorphism occurs for less than four monolayers. Above this thickness the difference in lattice parameters is accommodated by elastic strains and misfit dislocations. Recent applications of multiple diffraction analysis to the occurrence of pseudomorphism and strain in very thin metal films will be critically considered.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Structure and Tensile Properties of Thick Single-Crystal Silver Films Formed by Vacuum Deposition

S. Nagakura, K. Wakashima, and M. Fukamachi

J. Vac. Sci. Technol. 6, 611 (1969); http://dx.doi.org/10.1116/1.1315705 (4 pages)

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Single-crystal silver films of various surface orientations were prepared with thicknesses of 0.4–7 μ, and tensile tests were carried out for the films in as-deposited and annealed (860° C) states. Stress-strain curves were found to depend on the tensile direction and the film orientation. Structural observations were done with 500-kV and 1-MV electron microscopes. Dislocations are tangled in the as-deposited films thicker than 0.2 μ. Dislocation density is in the order of 1010∕ cm2. Twins and stacking faults do not exist. The annealing causes subgrain formation in (11̄0) and (111) films, but recrystallization in (001) films. Deformed structures are different according to the tensile directions. Based on the structural observations, the mechanical properties are discussed.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Observation of Dislocation Motion in Al Single-Crystal Films

S. Mader and P. Chaudhari

J. Vac. Sci. Technol. 6, 615 (1969); http://dx.doi.org/10.1116/1.1315706 (4 pages) | Cited 2 times

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Epitaxial Al films were evaporated onto polished surfaces of KCl substrates close to the orientation (123). They were single-crystal films with the substrate orientation and contained a few small twin-oriented inclusions. Portions of the films were mounted on an electron microscope straining stage and plastically deformed in uniaxial tension. They could be homogeneously strained by at least 1% before a crack develops. Dislocation motion was observed while the films were strained. In areas of homogeneous plastic flow, short dislocation lines extending from top to bottom surface of the film moved sideways on their {111} glide planes. They left slip traces on the surface which could be evaluated by diffraction contrast methods. A strong tendency for multiple slip was observed which depended on the relationships between Burgers vectors, film plane, and direction of applied stress.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Lk Linear defects: dislocations, disclinations

Mechanisms of Stress Relief in Thin Films

P. Chaudhari, S. Mader, and J. F. Freedman

J. Vac. Sci. Technol. 6, 618 (1969); http://dx.doi.org/10.1116/1.1315707 (4 pages) | Cited 4 times

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The stress required to form a dislocation loop of the size of a grain has been calculated for cases where the loop forms within a grain, at a grain boundary, and in grains adjacent to another grain where a loop is already present. It is shown that in typical polycrystalline films this value of the stress is comparable to the observed stresses in films before plastic flow sets in. In the case of single crystal epitaxial films with a high grown-in dislocation density the plastic strain realizable is shown on the basis of a simple model to be a few percent. The model is based on a simple nearest neighbor dislocation interaction and is shown to explain the tensile behavior of thin single crystal films.
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68.60.Bs Mechanical and acoustical properties

Stress in Vacuum-Deposited Films of Ag, Au, and Cu

Kunisuke Maki, Yuji Nakajima, and Koreo Kinosita

J. Vac. Sci. Technol. 6, 622 (1969); http://dx.doi.org/10.1116/1.1315708 (4 pages) | Cited 4 times

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The tension per unit width of the film S has been determined for Ag, Au, and Cu films deposited at 10−5 Torr from a few tens of angstroms up to 2000, 1500, and 1000 Å in thickness, respectively. S increases rapidly with the film thickness d until the film attains a thickness dI(=220∕320∕160math for Ag∕Au∕Cu films deposited at 2 Å∕sec). At dI the mean stress within the film σ(=S∕d) assumes a maximum. With thicker Ag and Cu films S remains nearly constant until at a thickness dII it starts to increase again. With Au films the rapid increase in S below dI is immediately followed by a slower increase with d. The first increase in S below dI is associated with the coalescence of islands. The second increase in S observed at larger thicknesses (d>dII for Ag and Cu, d>dI for Au) is probably due to residual gases. The last view is supported by experiments with Ag films deposited at 10−8 Torr.
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68.60.Bs Mechanical and acoustical properties
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Deformed Crystalline Parameter of Silver Microcrystals Deposited on Carbon

J. L. Sacedón, F. Catalina, and J. M. Rojo

J. Vac. Sci. Technol. 6, 625 (1969); http://dx.doi.org/10.1116/1.1315709 (4 pages)

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The present work shows the existence of silver microcrystals with contracted crystalline parameter in polycrystalline silver films evaporated in ultrahigh vacuum on amorphous carbon substrates. From these films the crystal thickness, the structure of the reciprocal lattice, the deformed parameter, and the stage where the anomalous crystal appears in the film growing sequence are found. We also show that these microscopic properties are related to the intrinsic stress measurements obtained by several workers on a macroscopic scale.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Solid Amorphous Ge and As as Examples of Lattice-Like Amorphous Substances

G. Breitling

J. Vac. Sci. Technol. 6, 628 (1969); http://dx.doi.org/10.1116/1.1315710 (4 pages) | Cited 7 times

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Amorphous Ge and As are lattice-like; they have the structural element in common with the respective lattice. Both elements show different amorphous states with various layer distances. In Ge the two shortest layer distances 2.43 and 2.70 Å are found whereas As yields three amorphous states with the shortest layer distances 3.15; 3.77 and 4.05 Å, respectively.
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61.43.Dq Amorphous semiconductors, metals, and alloys

Solid Amorphous Bi, Fe, and Ga as Examples of Liquid-Like Amorphous Substances

H. Richter

J. Vac. Sci. Technol. 6, 631 (1969); http://dx.doi.org/10.1116/1.1315711 (1 page) | Cited 1 time

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Solid amorphous Bi, Fe, and Ga are liquid-like, i.e., they have the same structure as the respective melt. However, the degree of order is higher than in the liquid state. A detailed analysis of the structure of liquid-like solid amorphous Bi and Fe (8-coordination) is given. Their atomic distribution curves are compared with those of molten Bi and Na (8-coordination). By discussion of the electron diffraction patterns of solid amorphous and of molten Bi one finds a layer lattice structure (IInd structure) which is derived from the appertaining lattice. The Fourier analysis of the intensity curves, however, demands the spherical close packing in the form of a straight atomic chain (Ist structure). Fujime’s electron diffraction patterns of solid amorphous Fe also show that there exist two structures simultaneously: a layer lattice structure of the appertaining lattice (IInd structure) and the spherical close packing, this time as a plane zigzag chain (Ist structure) as in molten Na. This double structure is also obtained in solid amorphous and in molten Ga. The noncrystalline Ga has an especially simple structure as found immediately by discussion of the intensity curve. In solid amorphous and in molten Bi, Fe, and Ga the simultaneous occurrence of two structures stabilizes the noncrystalline state.
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61.43.Dq Amorphous semiconductors, metals, and alloys

Conductivity of As–Te–I Films

R. B. Hilborn and Kanti Prasad

J. Vac. Sci. Technol. 6, 632 (1969); http://dx.doi.org/10.1116/1.1315712 (3 pages)

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The results of an investigation of the temperature dependence of the dc electrical conductivity of As–Te–I thin films are presented and interpreted as stemming from structural changes taking place in the films at elevated temperatures. Data are also given for the room temperature conductivity for films of various compositions and in various stages of devitrification.
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73.61.Jc Amorphous semiconductors; glasses

Preparation and Some Characteristics of Self-Supporting 300–2500 Å Oxide Films

A. Aladjem and D. G. Brandon

J. Vac. Sci. Technol. 6, 635 (1969); http://dx.doi.org/10.1116/1.1315713 (3 pages) | Cited 2 times

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An improved technique for the preparation of tantalum, niobium, and tungsten oxide films is described. Foils of the respective metal are anodically oxidized to the required thickness; by suitable masking, a non-oxidized area (with the exact shape and area of the desired “window”) is left on one side of the foil. The mask is removed and the metal is dissolved by making the foil the anode in an electrolyte consisting of an NH4Cl solution in methanol or in ethylene glycol. Self-supporting films, with a surrounding frame of residual metal and with an area up to 12 mm have been prepared by this technique. The films are pore-free, of adequate mechanical strength, and exhibit a high resistance to radiation damage when irradiated by alpha and beta particles. Their use in various devices, mainly for research in nucleonics, is being investigated.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
61.82.Ms Insulators

Structural Effects on Photoconduction in Amorphous Films of Organic Solids

D. J. Morantz and H. James

J. Vac. Sci. Technol. 6, 637 (1969); http://dx.doi.org/10.1116/1.1315714 (4 pages) | Cited 1 time

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Conduction in amorphous organic matrices, typically 10−18 mhos. and in photoexcited amorphous organic semiconductors, has received little attention. We have used systems consisting of inert matrices which are solid at 77 K in which we have dissolved one of several photoactive molecular species. These systems exhibit photocurrents of the order of 10−12 A or more. We have observed unique photocurrent transients on switching the irradiation light off or on. We report a detailed study of the effect of varying the composition of mixtures of ethanol and 3-methylpentane, which form the matrix, on the behaviour of 10−3 M solutions of phenanthrene. A conduction mechanism is outlined.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds

Formation of Grain Boundaries during Diffusion between Single-Crystal Films

J. W. Matthews and W. A. Jesser

J. Vac. Sci. Technol. 6, 641 (1969); http://dx.doi.org/10.1116/1.1315715 (4 pages) | Cited 1 time

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Diffusion between single-crystal films which are in contact and in parallel orientation is sometimes accompanied by the generation of grain boundaries. The grains enclosed by these boundaries are unusual in that their lattices are curved to accommodate the difference between the lattice parameters of the upper and lower specimen surfaces. In the regions outside these boundaries the gradient in lattice parameter is accommodated by misfit dislocations. The grain boundaries themselves are made up of dislocations which once accommodated misfit in the areas occupied by the curved grains. The formation of curved grains depends upon the misfit between the two crystals, and upon their relative thickness.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology

Low Temperature Diffusion in Polycrystalline Thin-Film Gold–Nickel Couples

J. L. Richards and W. H. McCann

J. Vac. Sci. Technol. 6, 644 (1969); http://dx.doi.org/10.1116/1.1315716 (4 pages) | Cited 7 times

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Diffusion in the gold–nickel system has been studied by isothermally annealing polycrystalline thin film gold-nickel couples in the temperature range 400°–750° C. X-ray diffractometer traces were taken of the couples after each annealing interval. The diffusion data are interpreted in terms of a model in which microcrystalline alloy aggregates of wide compositional range are formed in the grain boundaries of each layer. These aggregates become richer in diffused metal until compositions at the miscibility boundary are reached. Supersaturation and subsequent precipitation then occur to yield the terminal condition in which the couple becomes a uniform mixture of nickel-rich and gold-rich alloys.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
64.75.-g Phase equilibria

Diffusion in Thin Bi-Metal Films of Au–Cu

E. I. Alessandrini and J. D. Kuptsis

J. Vac. Sci. Technol. 6, 647 (1969); http://dx.doi.org/10.1116/1.1315717 (3 pages) | Cited 2 times

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For the study of diffusion in thin films, bulk methods such as radioactive tracers and sectioning techniques are not readily applicable because of the limited size and thickness of the specimens. This paper describes the use of electron microprobe spectroscopy as the analytical method for the detection of diffusion of Au into Cu films. Films prepared by evaporating 1500 Å of Cu on top of 100 Å Au were examined with the electron beam of the microprobe normal to the Cu film surface. Characteristic AuMα radiation was monitored at various accelerating voltages. This radiation requires a minimum of 2.2 kV for excitation beam voltage. It was not observed for as-deposited sandwich films until the beam was accelerated at 6 kV. The diffusion of Au into the Cu film, after various heat treatments, could be detected by the enhancement of the AuMα intensity and by the decrease of the minimum beam voltage necessary to just detect the characteristic AuMα signal. Data was obtained for the varying annealing conditions and were used to estimate the activation energy for the diffusion of the Au into the Cu film. The average value for E was found to be 0.8 eV ± 0.2 eV.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.60.Dv Thermal stability; thermal effects

Interdiffusion between Films of Gold and Silver

P. A. Turner, H. C. Theuerer, and K. L. Tai

J. Vac. Sci. Technol. 6, 650 (1969); http://dx.doi.org/10.1116/1.1315718 (1 page) | Cited 14 times

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A knowledge of diffusion rates in thin films is often necessary in order to predict the useful operating temperature range of thin film components. The few reported measurements available generally indicate that film diffusion rates at low temperatures (25°–300 °C) are substantially higher than would be inferred from extrapolations of bulk diffusion data to these temperatures. This is not surprising since high defect densities are common in films, and defects are known to act as high diffusivity paths. In this paper, measurements of diffusion rates are reported for films containing a range of defect densities. Films were prepared by evaporation and getter sputtering onto glass substrates. For each set of preparation conditions, films were characterized in terms of topography and defect density, by electron microscopy techniques. Diffusion rate measurements on Au∕Ag thin film couples were made by an optical reflectivity technique. Values of the diffusion coefficient for evaporated films typically lay in the range 10−15 to 10−17 for diffusion at temperatures between 100° and 200° C. For sputtered films values were about two orders of magnitude lower. Extrapolation of bulk D measurements to this temperature interval gives values of 10−21 and 10−27. A model for thin film diffusion is presented which relates the observed diffusivity with the defect content of the film.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Structure of Amorphous Alloy Films

C. N. J. Wagner

J. Vac. Sci. Technol. 6, 650 (1969); http://dx.doi.org/10.1116/1.1315719 (8 pages) | Cited 18 times

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Amorphous films are understood to be solids in which the postulated atomic arrangement shows no crystallike ordering beyond a few neighbors. The structure of such amorphous films is usually characterized by a diffuse x-ray or electron-diffraction pattern, consisting of a few broad rings or halos, and by a lack of contrast in transmission electron micrographs. However, very small, randomly oriented crystallites of <30 Å in diameter will also produce diffraction patterns which are qualitatively similar to those exhibited by amorphous solids. The theories of small-angle scattering and large-angle diffraction are discussed in terms of the structural disorder in the solids (electron-density fluctuations, atomic distributions, particle sizes) and are applied to the investigations of the structure of amorphous alloy films, such as liquid-quenched Fe–P–C and Pd–Si alloys, electrodeposited Ni–P alloys, and vapor-quenched Cu–Mg and Ag–Cu alloys.
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68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
61.05.C- X-ray diffraction and scattering
61.05.J- Electron diffraction and scattering

Preparation and Properties of Noncrystalline Films

J. D. Mackenzie

J. Vac. Sci. Technol. 6, 658 (1969); http://dx.doi.org/10.1116/1.1315720 (5 pages) | Cited 1 time

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Noncrystalline films can be prepared by many techniques. Broadly, these include deposition from the vapor phase, deposition from solutions, and quenching the liquid. The properties of such films can be significantly varied by changing the conditions of formation as well as by subsequent treatments. Examples of some of these aspects are reviewed particularly for oxide films. Scientifically, one of the most important questions is whether the structure, and hence properties, of non-crystalline films can vary significantly because of its preparation history. This problem will be discussed through examples of more recent work.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Electrical Conduction in Non-Metallic Amorphous Films

A. K. Jonscher and P. A. Walley

J. Vac. Sci. Technol. 6, 662 (1969); http://dx.doi.org/10.1116/1.1315721 (8 pages) | Cited 4 times

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The various mechanisms of electrical conduction and dielectric loss in non-metallic amorphous films are examined from the standpoint of their structure. A distinction is made between simple amorphous films such as silicon germanium and other semiconductors, glassy films, and, finally, noncrystalline polymers, both conducting and insulating. This distinction enables one to obtain some insight into the likely mechanisms which determine the dc conduction phenomena and the ac conduction or loss processes.
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73.61.Jc Amorphous semiconductors; glasses

Magnetoresistance of Nickel and Iron Single-Crystal Films

D. C. Larson, J. E. Christopher, R. V. Coleman, and Acar Isin

J. Vac. Sci. Technol. 6, 670 (1969); http://dx.doi.org/10.1116/1.1315722 (3 pages)

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Magnetoresistance measurements on single-crystal nickel and iron films have been made at temperatures of 4.2 to 295 K in fields of up to 50 kOe. The films were prepared by vacuum deposition onto heated rock salt and mica substrates producing films with (100) and (111) planes respectively, parallel to the film surface. The films varied in thickness from 500 Å to 5 μ and had resistivity ratios, ρ295∕ρ4.2, varying from 9 to 55. Transverse magnetoresistance curves taken at 295 K show crystalline anisotropies similar to those observed in bulk samples. At lower temperatures, the normal positive magnetoresistance is obtained, but anisotropies associated with the Fermi surface topology are not as marked as with bulk samples, due to the lower electron mean free paths of the electrons in film specimens. Both longitudinal and transverse magnetoresistance hysteresis curves were obtained for (100) nickel and iron films. An increased coercive force is obtained as the temperature is reduced for both nickel and iron films.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys

Current-Voltage Characteristics of S-Type in Some Film Systems and Its Interpretation

A. G. Zhdan, V. B. Sandomyrskyi, M. I. Elinson, and M. E. Tchugunova

J. Vac. Sci. Technol. 6, 673 (1969); http://dx.doi.org/10.1116/1.1315723 (1 page)

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Advances of investigations of switching phenomena in glassy semiconductors gives a possibility of a new interpretation of results on study of anomalous field emission (AFE) that we observed earlier on thin (1) layers of an amorphous quartz doped with carbon. The main AFE characteristics are quite similar to switching characteristics in glasses, namely, AFE current-voltage characteristics are of S-type and these characteristics have a high velocity of transition from a high ohmic state to low ohmic state. The AFE phenomenon is quite reproducible. On the emission pictures of AFE in the Muller microscope we observed a distinct narrow channel current which is typical for S-type characteristics. The current densities of AFE were=104math∕ cm2, the emission was stable in the relatively low vacuum (10−7 Torr). The velocity spectra of electrons in the AFE process are considerably wider than in the normal emission process. Thus the AFE method is quite an effective technique for investigating the physical mechanism of switching in similar systems. We have also investigated switching phenomena in single crystal film in the system Ge–CdS. In this system we also observed S-type characteristics with parameters that were a function of the Ge volume properties and of the condition of CdS deposition. The theory of the switching mechanism for the systems containing a high trap concentration was developed. This theory is based on the idea of space-charged limited currents and on the effect of the disappearance of local levels during screening by free carriers. The theory describes qualitatively many features of the switching phenomena in the glassy semiconductors.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.61.Jc Amorphous semiconductors; glasses

Magnetoresistance Effect in Thin Magnetic Structures

H. Roux-Buisson and J. C. Bruyere

J. Vac. Sci. Technol. 6, 673 (1969); http://dx.doi.org/10.1116/1.1315724 (4 pages)

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Magnetoresistance (MR) has been used to study inhomogeneous magnetic structures in thin films. From a known phenomenological law, it is possible to calculate for a given orientation of magnetization the electric fields in two perpendicular directions, so that one can plot a magnetoresistive loop as a function of magnetization orientation. We have studied two cases. (a) The angle α between magnetization and applied field in ferro-antiferromagnetic structure. In this case we have studied experimentally the MR loop and the curves α=f(θ), where θ is the angle between magnetic field and unidirectional axis. These results are similar to torque balance measurements obtained on the same structures. (b) The dispersion value ϵ of the magnetization versus the angle between mean magnetization and easy axis in simple films. In general, the dispersion value ϵ had been measured for a particular angle between magnetization and easy axis φ(φ=π∕2). By MR it is possible to obtain the results for all values of ϕ. Finally we have drawn the experimental curve ϵ=g(H) for φ=0 in a high-dispersion film and found the dispersion varying roughly as ϵ=ϵ0[HK∕(H+HK)].
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75.70.Ak Magnetic properties of monolayers and thin films

Preparation and Characteristics of Thin Films of Nickel Zinc Ferrite

N. J. Hellicar, A. Young, and J. V. Biggers

J. Vac. Sci. Technol. 6, 676 (1969); http://dx.doi.org/10.1116/1.1315725 (1 page)

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Thin films of nickel zinc ferrite have been prepared by rf sputtering, onto alumina substrates, at various temperatures. Measurement of remnant magnetisation combined with x-ray spectrographic data, enabled us to optimize conditions for the preparation of reproducible films. Chemical stoichiometry of the films was checked by x-ray probe analysis on a low-angle polished section of a film and by atomic absorption spectrometry on solutions of films in hydrochloric acid. The development of spinel phases in the films was followed using a high temperature x-ray camera. The existence of a wustite phase at the substrate film interface of films deposited onto “cold” substrates suggests that the material is transferred from the target as individual atoms of iron, nickel, and zinc. Stoichiometry of composition is not reached until considerable pre-sputtering has taken place. Films deposited on to cold substrates are amorphous. Considerable energy is required to recombine the individual oxides into a spinel phase. Structural homogeneity is dependent upon heat treatment. A similarity to bulk ceramic processing is indicated.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Enhanced Superconducting Transition Temperatures in Disordered, Mixed Film Materials

E. Guyon and F. Neunier

J. Vac. Sci. Technol. 6, 677 (1969); http://dx.doi.org/10.1116/1.1315726 (1 page) | Cited 2 times

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Thin superconducting “disordered” films are known to have enhanced thermodynamic critical properties. Various mechanisms can come into play. We have paid particular attention to the possible effect of favorable proximity of polarizable materials in close contact with superconductors. Two types of systems have been studied: (1) mixtures of superconductors and organic polarizable molecules (such as In anthraquinone, where Tc→4.6K); (2) co-deposited films of superconductors and semimetals or semiconductors (Tc=6.2K for In+10%  Ge; 6.45K for Al+10%Ge). This effect has to be substrated from the softening of phonon modes due to the existence of a large surface area in such systems. Quantitative information on the two mechanisms is obtained from electron tunneling experiments on the mixtures where the tunneling density of states and phonon spectrum can be analyzed.
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74.78.-w Superconducting films and low-dimensional structures
74.62.Yb Other effects

Critical Current Density and Critical Temperature Gradient in Thin Films of Type I Superconductors

R. P. Huebener and V. A. Rowe

J. Vac. Sci. Technol. 6, 677 (1969); http://dx.doi.org/10.1116/1.1315727 (4 pages)

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We have studied current induced and thermally induced flux motion through the flux flow resistivity and the Nernst effect, respectively, in superconducting films of lead, tin, and indium. The film thickness ranged between 0.5 and 11 μ. In addition to the flux flow resistivity and the transport entropy of a fluxoid, the critical current and the critical temperature gradient, at which current induced or thermally induced flux motion sets in, were determined. The critical current density and thereby the critical Lorentz force were found to increase strongly with decreasing film thickness. Further, with decreasing film thickness the critical Lorentz force became much larger than the critical thermal force. The experiments suggest that in a thin film the critical current is predominantly a surface current and that the critical surface currents contribute only very little to the Lorentz force on a fluxoid. Apparently, at and below its critical value the current flows in such a pattern that there is very little interaction with the fluxoids in the film.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
74.62.Yb Other effects

Surface-Thermal Modes in Simple Cubic Thin Films

A. Corciovei and D. Vamanu

J. Vac. Sci. Technol. 6, 680 (1969); http://dx.doi.org/10.1116/1.1315728 (4 pages) | Cited 2 times

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The paper reports dispersion law and polarization vectors for the modes of thermal vibration in a thin film, with special emphasis on the surface modes. The thin film is conceived as a superposition of q monatomic layers, which are (001), (110), or (111) crystallographic planes of a simple cubic lattice. The harmonic approximation for the nearest neighbors was used. The manner of treating the surface and spacelike thermal modes is suggested by a procedure used by Jelitto for spin wave modes. The surface thermal modes in thin films with symmetric surfaces are either of a symmetric (cosh), or of an antisymmetric (sinh) type. Their kind and number depend on the surface orientation and film thickness. For (001) surfaces the surface symmetric mode degenerates in a mode of constant amplitude across the film.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

The Effect of Light or Electron Beams on Thin Single-Crystal Films of Silver Iodide

R. Ostwald and K. G. Weil

J. Vac. Sci. Technol. 6, 684 (1969); http://dx.doi.org/10.1116/1.1315729 (3 pages) | Cited 2 times

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Experiments are reported on the rate of decomposition of thin single-crystal films of silver iodide on gold and silver (111) faces, by light and by 40 kV electrons. While the rate of decomposition by light is nearly independent of film thickness and temperature over a wide range of temperatures, there is a significant dependence on temperature, thickness, and substrate when 40 kV electrons are used as a decomposing agent. This leads to the conclusion that the process which depends on these parameters is the energy transfer from the high energy electrons to the electrons in the valence band of silver iodide. By the decomposition polycrystalline silver is formed. At temperatures above 300°C these small crystals are inserted into the underlying (111) face. Details of this process are studied by electron diffraction and by electron microscopy.
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61.82.Ms Insulators
61.80.-x Physical radiation effects, radiation damage

The Structure of Evaporated- and dc-Sputtered Films of Gold and Silver Deposited on Glass

K. L. Tai, P. A. Turner, and D. D. Bacon

J. Vac. Sci. Technol. 6, 687 (1969); http://dx.doi.org/10.1116/1.1315730 (3 pages)

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Evaporated- and dc-sputtered films of Au and Ag deposited on glass substrates were characterized in terms of topography and crystal size. The evaporated films exhibited less surface irregularity than the sputtered films, but contained a much wider range of crystal sizes. Little correlation was found between crystal size and surface topography.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Resistivity and Structure of Evaporated Aluminum Films

A. F. Mayadas, R. Feder, and R. Rosenberg

J. Vac. Sci. Technol. 6, 690 (1969); http://dx.doi.org/10.1116/1.1315731 (4 pages) | Cited 19 times

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Electrical resistivities have been measured at room temperature and at liquid helium temperature for evaporated aluminum films of variable thickness (t), and resistivity ratios (RR) computed. If a fixed value is assumed for the Fuchs surface scattering parameter p, then the results can only be interpreted in terms of changes in the intrinsic resistivity at 4.2 K, ρi, (and electron mean free path, li) with thickness. If totally diffuse scattering is assumed, then the values ρi≳0.164 μΩ⋅ cm, li≲5000 math for the thinnest films (≈1000 Å thick) and ρi≈0.0155 μΩ⋅ cm, li≈53 000 math for the thickest (≈10 000 Å thick) are obtained. X-ray-diffraction and electron-microscopy evidence suggests that the variation of ρi with thickness is caused by increasing grain size. Moreover, films thinner than ≈4000 Å have randomly oriented grains while those thicker than ≈6000 Å have a strong [111] fiber axis; the transition from random to preferred orientation appears to be associated with secondary features in the RR-vs-t curve.
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73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Electrical and Structural Properties of Co-Sputtered Tantalum–Aluminum Films

C. A. Steidel

J. Vac. Sci. Technol. 6, 694 (1969); http://dx.doi.org/10.1116/1.1315732 (5 pages) | Cited 7 times

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Tantalum-aluminum alloy films have been prepared by dc diode sputtering in argon from composite cathodes of tantalum sheet, with either inlaid strips of aluminum or aluminum strips attached to the tantalum. The aluminum coverage of the tantalum cathode has been varied between 0 and 85%. The coverages produced films ranging from 0% to about 85% aluminum, which are homogeneous in composition as determined by electron microprobe analysis. The as-deposited films of pure tantalum have either the bcc or β-Ta structure. Both structures form metastable solid solutions with up to 20 at.% aluminum. At 30% aluminum a new phase very similar to β-Ta appears. Between 30 at.% and 85 at.% aluminum a number of phases have been observed in the sputtered films but of the known bulk phases of the tantalum-aluminum system, Ta2Al, Ta17Al12, Ta12Al17, and TaAl3, only TaAl3 is observed in the sputtered films at 85% aluminum. The dependence of the electrical properties of tantalum-aluminum films on aluminum concentration has been determined. These properties include resistivity, dρ∕dT, Hall coefficient, carrier concentration and type, and Hall mobility. Results on alloy films are compared to those reported for the bulk aluminides Ta2Al and TaAl3.
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73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Field Induced Coalescence in Thin Metal Films

E. Ahilea and A. A. Hirsch

J. Vac. Sci. Technol. 6, 698 (1969); http://dx.doi.org/10.1116/1.1315733 (4 pages) | Cited 2 times

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The conductivity of samples of thin films of silver and platinum were investigated at temperatures ranging from liquid air down toward liquid helium temperature. It was found that electric field applied to the sample during deposition materially alters the characteristics of the films, making them more akin to those of thicker films. An explanation is suggested which is based on the permanent elongation of the film particles caused by an electric field.
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73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology