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Jul 1978

Volume 15, Issue 4, pp. 1219-1611


UPS and LEED studies of GaAs (110) and (111) As surfaces

Perry Skeath, W. A. Saperstein, P. Pianetta, I. Lindau, W. E. Spicer, and Peter Mark

J. Vac. Sci. Technol. 15, 1219 (1978); http://dx.doi.org/10.1116/1.569696 (4 pages) | Cited 2 times

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By comparison of LEED intensity–voltage data on GaAs (110) surfaces prepared by cleaving and by chemical etch followed by sputter annealing, we find the surfaces to be essentially the same in atomic geometry within the limits of experimental error. However, we find that important distinctions can be made between (110) surfaces prepared by these two methods when Fermi‐energy pinning and UPS data are considered. In this regard, we show that Fermi‐energy pinning is a particularly sensitive indicator of the degree of surface perfection and that the UPS data gives valuable information about the degree of perfection achieved by the different surface preparation techniques used. As an example of this, we show differences in the spatial distribution of damage on sputter‐annealed and heat‐cleaned surfaces which are seen by UPS. The sputtered surface is extremely imperfect prior to annealing. Finally, we find no evidence for intrinsic filled surface states in the band gap on the (111) As surface when prepared by heat cleaning or sputter annealing.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
81.65.-b Surface treatments

Surface and near‐surface atomic structure of GaAs (110)

A. Kahn, E. So, P. Mark, C. B. Duke, and R. J. Meyer

J. Vac. Sci. Technol. 15, 1223 (1978); http://dx.doi.org/10.1116/1.569697 (6 pages) | Cited 5 times

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Low‐energy electron diffraction (LEED) intensity–voltage data for a complete set of first‐order diffraction beams of the GaAs (110) surface is averaged at constant momentum transfer and compared with kinematical and dynamical model calculations for several surface atomic geometries. The atomic displacements in the surface and first two subsurface layers are obtained via this analysis. The influence of multiple scattering is examined by computing the single and multiple scattering contributions to the intensity–voltage profiles associated with atomic distortions within the first three lattice layers. This procedure allows the identification of the major features of the structure in the LEED–CMTA (constant momentum transfer average) profiles either with multiple scattering effects or with single scattering resonances derived from the lattice geometry.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Abstract: Theory of reconstruction‐induced subsurface strain

Joel A. Appelbaum and D. R. Hamann

J. Vac. Sci. Technol. 15, 1229 (1978); http://dx.doi.org/10.1116/1.569698 (1 page)

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Abstract Unavailable
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68.35.Ja Surface and interface dynamics and vibrations
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

On the geometrical structure of cleaved Si (111) surfaces

W. Mönch and P. P. Auer

J. Vac. Sci. Technol. 15, 1230 (1978); http://dx.doi.org/10.1116/1.569744 (7 pages) | Cited 4 times

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LEED intensity‐versus‐energy curves have been measured with clean, cleaved, and subsequently annealed Si (111) surfaces between 30 and 250 eV. After cleavage the surfaces exhibited single‐domain 2×1 LEED patterns. The analysis of the observed peak energies in the double‐diffraction picture confirms Haneman’s model of the 2×1 structure and gives: (1) The first layer is uniformly displaced inward by 0.08 Å and is buckled by 0.47 Å, (2) the spacing between second and third layer is relaxed by 0.22 Å. After anneals at approximately 300°C an apparent ′′1×1′′ structure is observed. The analysis of the measured I–V spectra reveals for this structure: The spacing between the first two layers is enlarged by 0.04 Å, while the distance between second and third layer is nearly unchanged. The I–V spectra of the final 7×7 structure, which are observed after anneals above the conversion temperature, are very similar to those of the ′′1×1′′ structure.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Self‐consistent study of the (2×1) reconstructed Si(111) surface

C. T. White and K. L. Ngai

J. Vac. Sci. Technol. 15, 1237 (1978); http://dx.doi.org/10.1116/1.569745 (7 pages) | Cited 1 time

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Si(111) surfaces formed by cleavage in ultrahigh vacuum initially exhibit a 2×1 LEED pattern which is replaced by an effective 1×1 pattern upon annealing at moderate temperatures. Concomitant with the replacement of the 2×1 structure with the 1×1 pattern, a large change in the electronic workfunction is observed. To study the 2×1 and its transformation, we have constructed a model based on Harrison’s idea of dehybridization energy‐mediated reconstruction. Results obtained from a self‐consistent analysis of this model show that a 2×1 pattern, corresponding to a split dangling bond band, is unstable at several hundred degrees Kelvin towards an effective 1×1 pattern with an unsplit dangling bond band and appreciably higher Fermi level consistent with experiment.
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73.20.-r Electron states at surfaces and interfaces

(110) surface states of GaAs and matrix element effects in angle‐resolved photoemission

D. J. Chadi

J. Vac. Sci. Technol. 15, 1244 (1978); http://dx.doi.org/10.1116/1.569746 (5 pages)

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The relaxed (110) surface electronic structure of GaAs is calculated within the tight‐binding model. The symmetry and dispersion of the surface states are compared to those measured by angle‐resolved photoemission experiments. Variations in photoemission intensity with measurement geometry are related to matrix‐element modulation effects and it is shown that angle‐resolved measurements can give information on the symmetry of surface states.
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73.20.-r Electron states at surfaces and interfaces
81.65.-b Surface treatments

Symmetry determination of surface states on GaAs (110) using polarization‐dependent, angle‐resolved photoemission

G. P. Williams, R. J. Smith, and G. J. Lapeyre

J. Vac. Sci. Technol. 15, 1249 (1978); http://dx.doi.org/10.1116/1.569747 (3 pages) | Cited 6 times

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New occupied surface states are observed on the (110) cleavage face of GaAs. Using the polarized character of the radiation at the Wisconsin Synchrotron Radiation Center the symmetry of the states in the mirror plane are determined. Among current calculations of the electronic structure, only that which includes bond length relaxation yields results that are consistent with the observations.
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73.20.-r Electron states at surfaces and interfaces
81.65.-b Surface treatments

Surface electronic structure studies of GaAs (110)

J. A. Knapp, D. E. Eastman, K. C. Pandey, and F. Patella

J. Vac. Sci. Technol. 15, 1252 (1978); http://dx.doi.org/10.1116/1.569748 (4 pages) | Cited 3 times

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Angle‐resolved photoemission using synchrotron radiation from GaAs (110) has been studied in conjunction with tight binding calculations of the surface electronic structure. Emission from two new surface resonances−which were predicted to exist only for a relaxed surface‐have been identified near the edges of the surface Brillouin zone at ? and ?′. Also, measurements of the dispersion of the As‐derived surface state near the valence band maximum, first reported elsewhere, have been extended from ? to the zone edge ? and a band width of 0.6 eV has been determined. All of these observations, including those reported elsewhere of intrinsic surface states on GaAs (110) are accounted for by a tight binding model calculation for a relaxed surface (∠19° bond angle rotation).
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73.20.-r Electron states at surfaces and interfaces
81.65.-b Surface treatments

Surface bands in relaxed cleavance surface of GaP

C. M. Bertoni, O. Bisi, F. Manghi, and C. Calandra

J. Vac. Sci. Technol. 15, 1256 (1978); http://dx.doi.org/10.1116/1.569749 (6 pages) | Cited 4 times

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We have studied the dependence of the surface states upon relaxation in GaP (110) surface. Calculations were performed using a tight binding model with an approximate treatment of the self‐consistency. Different relaxation models, involving both rotation and stretching of the bonds were considered. The location and orbital composition of the surface bands their dispersion and the local density of states at the surface are presented for the various models. Unlike the other III–V compounds, we find that the relaxation does not remove the empty surface states from the band gap. Such a conclusion agrees with the experimental information on the pinning of the Fermi level in n‐doped samples of GaP. A comparison with partial‐yield photoemission data and a theoretical estimate of the surface excitonic binding energy are also given.
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73.20.-r Electron states at surfaces and interfaces

Surface final‐state effects in core electron transition energies

J. C. McMenamin and R. S. Bauer

J. Vac. Sci. Technol. 15, 1262 (1978); http://dx.doi.org/10.1116/1.569750 (4 pages) | Cited 1 time

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The empty states of semiconductor surfaces have been probed by exciting surface core electrons and measuring the constant‐final‐state partial yield. We have previously reported the wavefunction symmetry and atomic composition of semiconductor surface states deduced from these data. Here we discuss the determination of the energy of these surface states relative to the bulk conduction bands. The surface transition‐energy is always less than the separation of the energy levels measured in direct photoemission. We show that the experimental uncertainties in applying this additivity principle always result in a lower limit for that difference. Although the empty surface states cannot yet be located precisely, analysis of our experimental data has revealed a definite trend toward increasing surface‐state final‐state shift with decreasing semiconductor polarizability. This trend is not observed for conduction band states at the surface or in the bulk, thereby allowing us to pose arguments concerning the relative contributions to the observed final‐state shifts of relaxation, electron‐hole interactions, and dielectric function discontinuity at the surface.
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73.20.-r Electron states at surfaces and interfaces

Abstract: Electronic structure of semiconductor interfaces

Marvin L. Cohen

J. Vac. Sci. Technol. 15, 1266 (1978); http://dx.doi.org/10.1116/1.569751 (1 page)

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Abstract Unavailable
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ns Metal-nonmetal contacts

Wave functions and (110) surface structure of III–V compounds

D. J. Miller and D. Haneman

J. Vac. Sci. Technol. 15, 1267 (1978); http://dx.doi.org/10.1116/1.569752 (7 pages) | Cited 1 time

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New electron paramagnetic resonance determinations of the dangling orbital on Ga atoms on the cleavage surfaces of GaP are compared with corresponding data for GaAs and A1Sb. Using a bond‐orbital approach the (110) surface structure for all three compounds is reconstructed, with the surface cation withdrawing towards a near planar configuration with its three neighbors. The EPR results provide the first opportunity of experimentally evaluating surface‐charge densities calculated by the pseudopotential method. Surface wavefunctions determined from the measurements are compared with the results of self‐consistent pseudopotential calculations of GaAs surfaces, with and without the above reconstruction. It is concluded from this and other information, that current pseudocharge densities for surfaces are not reliable, due in part to the use of a local form of the pseudopotential.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
76.30.-v Electron paramagnetic resonance and relaxation

Theoretical studies of Si and GaAs surfaces and initial steps in the oxidation

William A. Goddard III, John J. Barton, Antonio Redondo, and T. C. McGill

J. Vac. Sci. Technol. 15, 1274 (1978); http://dx.doi.org/10.1116/1.569753 (13 pages) | Cited 11 times

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Using ab initio quantum chemical methods (generalized valence bond), we examine (i) the electronic states of Si (111) and GaAs (110) surface, (ii) the relaxation of the Si (111) surface, (iii) the reconstruction of the GaAs surface, (iv) the initial steps in the chemisorption of O2 on Si (111), and (v) the bonding of O atom to Ga and As centers.
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73.20.-r Electron states at surfaces and interfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Extrinsic surface states for oxygen chemisorbed on the GaAs (110) surface

J. D. Joannopoulos and Eugene J. Mele

J. Vac. Sci. Technol. 15, 1287 (1978); http://dx.doi.org/10.1116/1.569754 (3 pages)

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The electronic structure of various configurations of oxygen chemisorbed on GaAs (110) is studied using a localized orbital approach. Recent conflicting interpretations of experimental measurements, concerning the site of chemisorption, are resolved. It is concluded that for low averages, oxygen prefers to chemisorb to the surface arsenics and chemisorbs as an O2 molecule.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Abstract: Bonding states of oxygen on silicon

C. M. Garner, I. Lindau, C. Y. Su, P. Pianetta, and W. E. Spicer

J. Vac. Sci. Technol. 15, 1290 (1978); http://dx.doi.org/10.1116/1.569755 (2 pages)

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Abstract Unavailable
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.-b Surface treatments

Oxygen uptake on an epitaxial PbSnTe(111) surface

T. S. Sun, S. P. Buchner, N. E. Byer, and J. M. Chen

J. Vac. Sci. Technol. 15, 1292 (1978); http://dx.doi.org/10.1116/1.569756 (6 pages) | Cited 4 times

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The oxygen uptake of a molecular‐beam‐epitaxial Pb0.8Sn0.2Te(111) surface has been investigated by AES, XPS, and UPS studies. The results indicate a strong affiliation of oxygen with Sn ions. Oxidation of Sn starts at an exposure of 104 L, whereas oxidation of Pb and Te starts at an exposure of 106 L. Evidence indicates that Sn ions diffuse from the bulk to the surface in the process of oxygen chemisorption. A sharp increase of oxygen uptake is observed at an exposure of 106 L. It marks the commencement of the oxidation process in which bonds between the surface constituents break in favor of individual affiliation with oxygen. A comparison of these results with those previously obtained for PbTe will be discussed.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.05.Bx Metals, semimetals, and alloys
79.20.Fv Electron impact: Auger emission
81.65.-b Surface treatments

Reactions of oxygen with ZnO–101̄0‐surfaces

W. Göpel

J. Vac. Sci. Technol. 15, 1298 (1978); http://dx.doi.org/10.1116/1.569757 (13 pages) | Cited 19 times

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Investigations are reported on the reaction of oxygen with electrostatic neutral ZnO–101̄0‐surfaces studied by means of AES, LEED, EPR, thermal desorption spectroscopy, and isotopic exchange as well as changes in the surface conductivity and work function. Geometric and electronic structures of the surface are discussed. Reversible physisorption data are determined in the range of 120–250 K (ϑ<10−1 for P<10−4 Pa), from which adsorption isotherms and isosteric heats of adsorption are derived. Chemisorption is found in the range of 300–650 K (ϑ<2.5×10−4) on crystals with negligible amount of point defects at the surface. The energy of chemisorption and reaction rates can be described quantitatively by electron transfer models. Desorption rates for zinc and oxygen are derived from measurements of instationary crystal sublimation, the latter being strongly dependent on thermodynamically stable concentrations of oxygen vacancies at the surface, which can be determined quantitatively and removed during reactions with oxygen at lower temperatures (T?700 K). Under these conditions a strong influence of oxygen vacancies on sticking coefficients and rates of electron transfer during oxygen exposure is found. The separation of chemisorption processes and reactions with point defects during oxygen interaction enables a deeper understanding of elementary steps during catalysis on ZnO.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.20.-r Electron states at surfaces and interfaces
73.25.+i Surface conductivity and carrier phenomena
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Measurement of valence band Auger spectra for GaAs(110) from Ga and As CCV transitions.

G. D. Davis and M. G. Lagally

J. Vac. Sci. Technol. 15, 1311 (1978); http://dx.doi.org/10.1116/1.569758 (6 pages) | Cited 1 time

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The line shapes of the Ga and As M1M45V and M23M45V Auger transitions in cleaved GaAs(110) have been measured. The line shapes are quite different, indicating that the Auger effect gives a measure of the density of filled states local to the atomic species with the initial core hole. Comparisons with the calculated local density of states for one model of the GaAs(110) surface and with Auger transitions derived for this model are made. A total transition density of filled states is synthesized by adding the Ga and As results and is compared with photoelectron spectroscopic measurements. The resulting good agreement indicates that hole–hole interactions are not severe in this system.
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79.20.Fv Electron impact: Auger emission
71.20.-b Electron density of states and band structure of crystalline solids

Application of Auger electron spectroscopy to studies of the silicon/silicide interface

John A. Roth and C. R. Crowell

J. Vac. Sci. Technol. 15, 1317 (1978); http://dx.doi.org/10.1116/1.569759 (8 pages) | Cited 25 times

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We discuss the use of Auger electron spectroscopy to obtain chemical state information about the transition‐metal/Si and silicide/Si interfaces. Characteristic Si L2,3VV Auger spectra for silicides of nine different transition metals are presented and analyzed in terms of chemical bonding in the compounds. The use of Auger peak shape analysis to obtain depth profiles of chemical state is illustrated by the detection of thin silicide layers at the metal/Si interface in as‐deposited samples. The possibility of chemical state changes induced by inert gas ion bombardment is discussed and this effect is proposed to explain almost identical Si LVV peak shapes observed for different silicides of a particular transition metal. Pd2Si is shown to be stable against bombardment‐induced bonding changes, and for this system sequential deposition studies of Pd on Si yield basically the same information as does sputter profiling.
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73.40.Ns Metal-nonmetal contacts
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Structural studies of thin nickel films on silicon surfaces

W. J. Schaffer, R. W. Bené, and R. M. Walser

J. Vac. Sci. Technol. 15, 1325 (1978); http://dx.doi.org/10.1116/1.569760 (7 pages) | Cited 11 times

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Thin nickel films rf sputtered onto both (100) and (111) oriented silicon produce amorphous surface regions, as indicated by transmission electron diffraction (TED), in the equivalent thickness range 10?t?28 Å. AES measurements indicate to contaminants in these thin layers. Annealing 10‐Å films at 400°C for one hour does not alter the pattern. At 15 Å, however, the anneal produces polycrystalline rings of δ‐Ni2Si. In unannealed samples, Ni2Si polycrystalline rings are seen at a minimum deposited metal thickness of 30 Å and AES measurements show a splitting in the 92‐eV silicon line previously reported for Ni2Si. Both NiSi and Ni2Si polycrystals are seen via TED at a deposition thickness of 120 Å upon anneal at 300°C for 30 minutes. These measurements indicate that Ni2Si is nucleated from an amorphous region whose structure (as indicated by TED) is independent of the amount of the Ni sputtered onto the substrate. This result is consistent with our published model of silicide nucleation.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
81.05.Kf Glasses (including metallic glasses)
81.15.Cd Deposition by sputtering

New phenomena in Schottky barrier formation on III–V compounds

I. Lindau, P. W. Chye, C. M. Garner, P. Pianetta, C. Y. Su, and W. E. Spicer

J. Vac. Sci. Technol. 15, 1332 (1978); http://dx.doi.org/10.1116/1.569761 (8 pages) | Cited 18 times

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The possibility of a defect mechanism is proposed to explain the Fermi‐level pinning in Schottky barriers on III–V semiconductor surfaces. This suggestion comes from the results of photoemission spectroscopy applied to the study of formation of metal–semiconductor barrier heights. Changes in the electronic structure and composition of the interface are studied. For Au metal overlayers on the (110) surfaces of GaAs, GaSb, and InP, the Fermi‐level pinning occurs at 0.1 or less of a monolayer coverage. Furthermore, the pinning position is roughly independent of the choice of adatom: Cs, Al, Au, or O. The partial yield structure disappears at about monolayer coverage of Au. The Au valence band had the characteristic shape for atomiclike Au, indicating that the metal was dispersed homogeneously on the surface without the formation of thick islands. Deposition of Au onto the GaSb surface causes the compound to decompose. The antimony segregates to the surface and leaves behind a nonstoichiometric interface. The results for GaSb are compared to those for GaAs(110) and InP(110), where removal takes place of both semiconductor constituents in the interface.
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73.40.-c Electronic transport in interface structures
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.-b Surface treatments

Metal–semiconductor surface and interface states on (110) GaAs

R. Z. Bachrach

J. Vac. Sci. Technol. 15, 1340 (1978); http://dx.doi.org/10.1116/1.569762 (4 pages) | Cited 6 times

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Photoemission studies have been carried out for aluminum and gallium metal surfaces and metal–GaAs interfaces. Core chemical shifts and valence band changes have been simultaneously investigated with the wide photon energy range available on the 4° beam line at the Stanford Synchrotron Radiation Laboratory. These experiments show that although studies of the individual surfaces provide useful reference information, the separate character of the free surfaces is dominated upon interface formation by chemical changes and bond formation. The studies have shown that, for a simple metal such as aluminum, surface states and charge localization are important on specific crystalline faces. These states can affect the interface that forms between a metal and a semiconductor. For the Ga–GaAs interface investigated as the interface is formed, no Schottky barrier is found for Ga on p‐type GaAs. Charge transfer from the surface As atoms to the Ga overlayers occurs, and some As migrates into the overlayer resulting in vacancies at the interface. Valence band changes with Ga coverage show that at least two occupied inteface states arise. These states, at −4.2 and −5.8 eV, fall within the gap in the surface Brillouin zone for projected bulk states. With alumimum an exchange reaction takes place, leaving an interfacial layer of AlAs and a GaAl alloy at the interface.
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73.40.Ns Metal-nonmetal contacts
73.20.-r Electron states at surfaces and interfaces
81.65.-b Surface treatments

Schottky barriers on ordered and disordered surfaces of GaAs(110)

A. Amith and P. Mark

J. Vac. Sci. Technol. 15, 1344 (1978); http://dx.doi.org/10.1116/1.569763 (9 pages) | Cited 18 times

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The properties of gold Schottky barriers on the GaAs(110) surface were measured to determine the influence of atomic order, cleanliness and surface processing. Clean and ordered surfaces were prepared by ion bombardment and thermal annealing. Their chemical condition was monitored by AES and their atomic order by LEED. Some surfaces were subsequently disordered by further ion bombardment or by exposure to oxygen; others were not subjected to any further processing. Gold dots were evaporated on all surfaces without breaking the UHV. No significant differences among barrier height values measured by internal photoemission were observed, suggesting Fermi‐level pinning for all junctions. Major and consistent differences in capacitance–voltage and in current–voltage measurements were found between clean and ordered surfaces, and disordered surfaces. The experimental results indicate that transport across the barriers is very sensitive to inhomogeneities in the layers adjacent to the metallurgical junction introduced during the various steps employed in cleaning and ordering the surface. Chemical polishing, sputter etching and annealing all affect the stoichiometry at the surface. Annealing by itself appears to produce an intrinsic layer and while it results in ordering of the surface, it does not eradicate defects and other spatial inhomogeneities, nor the drastic changes in the electronic properties which are introduced in the surface by sputtering. Surfaces may have the same structure and ordering, yet differ widely in their electronic properties. Seeming inconsistencies among results of different measurement methods are ascribed to the fact that each method probes a different region and is sensitive to different conditions.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.05.Bx Metals, semimetals, and alloys

Silver contact on GaAs (001) and InP (001)

J. Massies, P. Devoldére, and N. T. Linh

J. Vac. Sci. Technol. 15, 1353 (1978); http://dx.doi.org/10.1116/1.569764 (5 pages) | Cited 12 times

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We report here the first results of our study of metal/III–V semiconductor contacts :Ag–GaAs (001) and Ag–InP (001). Clean GaAs (001) and InP (001) surfaces, under various conditions of stoichiometry, are obtained by ion etching followed by annealing and arsenic or phosphorous adsorption and carefully characterized by AES, LEED, and ELS. Using these techniques some correlations between surface stoichiometry, surface structures, and electronic surface states have been found. On these surfaces the metallization has been carried out by an MBE‐like technique. The results obtained show that the Schottky barrier height changes according to the conditions of surface preparation. To explain these results, different hypotheses are discussed.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions

Dissolution of amorphous silicon into solid aluminum

R. A. Scranton and J. O. McCaldin

J. Vac. Sci. Technol. 15, 1358 (1978); http://dx.doi.org/10.1116/1.569765 (4 pages) | Cited 4 times

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The rate of dissolution of amorphous Si into solid Al is measured at temperatures below 400°C. The dissolution rate is found to be much faster than predicted by a simple model of the transport of Si through Al. This result is related to defects in the growth of epitaxial Si using the solid‐phase epitaxy process.
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81.40.Gh Other heat and thermomechanical treatments
66.30.-h Diffusion in solids
68.55.-a Thin film structure and morphology

Influence of the free surface on the electrical behavior of metal contacts to p‐InAs

M. F. Millea and A. H. Silver

J. Vac. Sci. Technol. 15, 1362 (1978); http://dx.doi.org/10.1116/1.569766 (8 pages) | Cited 5 times

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The study of electrical (evaporated gold) contacts to p‐InAs has been extended down to an acceptor doping of 2×1016 cm−3. The steady‐state current–voltage characteristic is independent of the free surface, except for a reverse‐breakdown effect which appears to be surface dependent. A space‐charge generation‐recombination mechanism is proposed to explain the carrier flow for contacts on low‐doped p‐InAs. The free surface is found to strongly influence both the capacitance and photoresponse of gold contacts evaporated on low‐doped p‐InAs. A novel technique employing combined photocurrent and capacitance measurement has been employed to investigate the electrical characteristic of the free surface. With this technique we can easily determine both the spatial and temporal variation of the surface sheet resistance. For a freshly etched surface the surface electron concentration is small and spatially variable; with time the surface electron concentration increases. This indicates that although the conduction band minimum at the surface is below the Fermi level, the lowest quantized surface electron level is above the Fermi level.
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73.40.Ns Metal-nonmetal contacts

Intrinsic surface states and Fermi‐level pinning at metal–semiconductor interfaces

Eugene J. Mele and J. D. Joannopoulos

J. Vac. Sci. Technol. 15, 1370 (1978); http://dx.doi.org/10.1116/1.569789 (4 pages)

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We find that the well‐known transition in the Fermi‐level pinning behavior of metal–semiconductor contacts can be quantitatively characterized in a fundamental way. Our model makes use of the clean semiconductor surface state energies, predicts the onset of the covalent–ionic transition, and explains strong Fermi‐level pinning at metal contacts to covalent materials with large optical gaps and low bond polarizabilities.
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73.40.Ns Metal-nonmetal contacts

Chemical trends of Schottky barriers: A reexamination of some basic ideas

M. Schlüter

J. Vac. Sci. Technol. 15, 1374 (1978); http://dx.doi.org/10.1116/1.569790 (3 pages) | Cited 9 times

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Fundamental experimental data on metal–semiconductor interfaces are reexamined. It is found that the previously reported abrupt transition in Schottky barrier behavior between covalent and ionic semiconductors is not that clearly defined and diffused by data scattering. Furthermore, the data show no saturation of the linear interface parameter S for S=1. Considering the correct definition of S, it follows that the true Schottky limit can only approximately be described by S and should occur for some value S?2.0–3.0 rather than for exacatly S=1 as previously claimed.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions

Abstract: Pseudopotential calculations of the electronic structure of germanium and diamond Schottky barriers

J. Ihm, Steven G. Louie, and Marvin L. Cohen

J. Vac. Sci. Technol. 15, 1377 (1978); http://dx.doi.org/10.1116/1.569791 (1 page)

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Abstract Unavailable
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

Chemical reaction and charge redistribution at metal–semiconductor interfaces

L. J. Brillson

J. Vac. Sci. Technol. 15, 1378 (1978); http://dx.doi.org/10.1116/1.569792 (6 pages) | Cited 34 times

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Interface compound formation and metal‐induced surface states are observed at representative metal–semiconductor interfaces. These phenomena are associated with microscopic dipoles at the intimate contacts which account for the macroscopic Schottky barrier heights. The barrier heights exhibit a correlation with chemical reactivity and display a pronounced transition between reactive and unreactive interfaces. Thus, local charge redistribution rather than any intrinsic surface states of the semiconductor determine Schottky barrier formation at the metal–semiconductor interfaces.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Md Surface thermodynamics, surface energies
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Ns Metal-nonmetal contacts

A theoretical study of Al overlayers on Si(111)

H. I. Zhang and M. Schlüter

J. Vac. Sci. Technol. 15, 1384 (1978); http://dx.doi.org/10.1116/1.569793 (5 pages) | Cited 4 times

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The surface system Si(111) with chemisorbed monolayers of Al is investigated theoretically. Within the self‐consistent pseudopotential scheme several different structural models for chemisorption are studied and spectroscopic results are compared to recent experimental photoemission and electron energy loss data obtained on similar systems. It is found that chemical bonds between substrate and metal are formed yielding states in the semiconductor gap which stabilize the Fermi level. From the detailed analysis of several strong spectroscopic features it follows that the interface may structurally be modelled by Al atoms sitting in threefold coordinated positions either above the Si(111) surface or replacing the outermost silicon layer, (i.e., Lander’s substitutional model).
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions

Covalent–ionic trend at Schottky barrier interfaces in a pairing model

K. L. Ngai and C. T. White

J. Vac. Sci. Technol. 15, 1389 (1978); http://dx.doi.org/10.1116/1.569794 (8 pages) | Cited 3 times

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We discuss from a theoretical point of view the expected effects of electron pairing states on metal semiconductor interfaces. Several microscopic models are developed which depend on the presence of electron–electron pairing interactions mediated through nonbonded orbitals thought to be present at the interface. It is found that a picture which associates the nonbonded states with metal–anion bonds has a number of features consistent with experiment.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.-c Electronic transport in interface structures

Effects of ultrathin oxides in conducting MIS structures on GaAs

R. B. Childs, J. M. Ruths, T. E. Sullivan, and S. J. Fonash

J. Vac. Sci. Technol. 15, 1397 (1978); http://dx.doi.org/10.1116/1.569795 (5 pages) | Cited 7 times

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Barrier formation in Schottky barrier‐type devices (metal–semiconductor and metal–thin‐film insulator–semiconductor structures) is examined as a function of purposeful oxidation of the semiconductor surface and semiconductor surface etch. Metallizations used are thin‐film (125–200 Å) Au, Ag, Pd, and Al. Acid and basic etches were employed. Evolution of the barrier with purposeful oxidation is measured by reverse C–V barrier height deteminations, dark I–V barrier height, photoresponse barrier height, and photovoltaic open circuit voltage. For the metals examined on n‐type GaAs, the oxidation procedure used resulted in the MIS structures having higher barrier heights than the corresponding baseline MS devices. This cannot be explained simply in terms of the increased, geometrical separation of the metal and semiconductors with oxidation. It does not seem to be explained in terms of the oxidation satisfying bonds at the GaAs interface. Rather, trapping and perhaps chemical interactions are involved in the barrier formation. The evolution of the barrier with purposeful oxidation is similar for Au and Pd. For these devices (with ideality factors ? unity) the change in reverse C–V barrier height with oxidation equals the change in photovoltaic open circuit voltage. These devices were generally stable. Silver and aluminum devices exhibited strong charge trapping in the interfacial region.
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72.40.+w Photoconduction and photovoltaic effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Ng Insulators

Electrical properties of the gallium arsenide–insulator interface

L. G. Meiners

J. Vac. Sci. Technol. 15, 1402 (1978); http://dx.doi.org/10.1116/1.569796 (6 pages) | Cited 34 times

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Extensive capacitance–voltage (C–V) measurements have been performed on three types of insulators on n‐type GaAs: pyrolytically deposited silicon nitride, sputtered silicon nitride, and the oxide produced by anodization. Evaporated aluminum gate contacts and alloyed Au–Ge ohmic contacts were applied and the C–V characteristics of these structures were measured from the quasistatic regime to 150 MHz. Although differences in detail are seen at intermediate frequencies, the data taken at the extreme frequency limits differ very little for the three types of specimens. The quasistatic and high‐frequency data are consistent with a model wherein the surface potential with zero applied gate bias is ∠−0.8 V. Application of electric fields of the order of ±106 V/cm at the semiconductor surface results in movement of the surface potential across approximately 1/3 of the band gap. An accumulation layer of surface electrons could not be produced on any of the devices tested.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Measurement of MIS capacitors with oxygen‐doped AlxGa1−xAs insulating layers on GaAs

H. C. Casey, A. Y. Cho, D. V. Lang, and E. H. Nicollian

J. Vac. Sci. Technol. 15, 1408 (1978); http://dx.doi.org/10.1116/1.569797 (4 pages) | Cited 8 times

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Metal–insulator–semiconducator capacitors were prepared by doping an Al0.5Ga0.5As layer with oxygen to demonstrate a lattice‐matched single‐crystal insulator–semiconductor heterojunction. Crystal growth was by molecular‐beam epitaxy, and measurements were made on n‐type GaAs–Al0.5Ga0.5As–Cr/Au MIS capacitors. Both the absence of hysteresis in the C–V measurements and the absence of observable interface traps by deep‐level transient spectroscopy (DLTS) suggest a very small semiconductor–insulator interface trap concentration. Measurement of the admittance as a function of temperature at different frequencies permitted the observation of the dominant deep level in the oxygen‐doped Al0.5Ga0.5As–GaAs. This level is at 0.64±0.04 eV with a concentration of ∠1×1017 cm−3. Current–voltage measurements show space‐charge‐limited currents for forward and reverse biases. These initial measurements on Cr/Au–Al0.5Ga0.5As–GaAs MIS capacitors have shown that insulating behavior can be obtained with oxygen‐doped AlxGa1−xAs and the properties are sufficiently promising to investigate the MIS device potential of this lattice‐matched heteojunction.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
84.32.Tt Capacitors

Electronic states of impurities located at or near semiconductor–insulator interfaces

Nunzio O. Lipari

J. Vac. Sci. Technol. 15, 1412 (1978); http://dx.doi.org/10.1116/1.569798 (5 pages) | Cited 6 times

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We solve the effective mass equations describing donor impurities localized at semiconductor–insulator interfaces using a method which involves an expansion of the impurity wavefunction in terms of spherical harmonics. We also investigate the behavior of the impurity energies as a function of the donor distance from the interface both in the insulator and in the semiconductor. This allows, for the first time, the connection between surface and bulk donor properties. Results for the Si–SiO2 case are presented.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Study of semiconductors using electrochemical techniques

S. Roy Morrison

J. Vac. Sci. Technol. 15, 1417 (1978); http://dx.doi.org/10.1116/1.569799 (5 pages) | Cited 4 times

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A nonmathematical description of current flow across the semiconductor–electrolyte boundary is presented. The description of active ions in solution is reviewed in terms of their acceptor or donor energy levels, the fluctuation of these levels, and the mechanism of electron transfer to or from these levels. With no such active ions (in other words, with an inert electrolyte), in principle electron transfer cannot occur. The use of such an inert electrolyte as a contact to make measurements of the bulk properties of the semiconductor is emphasized. The advantages and disadvantages of such a liquid as opposed to a metallic layer as a contact in C–V studies is discussed.
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73.40.Mr Semiconductor-electrolyte contacts

Electrolytic decomposition and photodecomposition of compound semiconductors in contact with electrolytes

Heinz Gerischer

J. Vac. Sci. Technol. 15, 1422 (1978); http://dx.doi.org/10.1116/1.569800 (7 pages) | Cited 20 times

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Electrons and holes affect the bond strength of surface atoms. Therefore, in most systems their surface concentration controls the rate of electrolytic decomposition reactions. The thermodynamics of such reactions are characterized by their redox potentials which are equivalent to the Fermi energies of electrons or holes. It is shown that the energy positions of the redox Fermi levels for decomposition with respect to the position of the band edges and the Fermi levels of competing redox reactions, give an immediate indication for the susceptibility of a semiconductor to electrolytic decomposition. This concept is especially useful for the discussion of photodecomposition where the electronic free energy can be described by individual quasi‐Fermi levels for electrons and holes. Data are given for the semiconductors ZnO, TiO2, Cu2O, CdS, MoS2, GaP, and GaAs. A model for bond breaking by holes at a kink site of a compound semiconductor is discussed to demonstrate what role the surface bond character plays for the height of activation barriers and how kinetics modify the thermodynamic conclusions on stability.
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82.45.-h Electrochemistry and electrophoresis
68.35.Md Surface thermodynamics, surface energies
73.40.Mr Semiconductor-electrolyte contacts

Stabilization of n‐type semiconductors to photoanodic dissolution: II–VI and III–V compound semiconductors and recent results for n‐type silicon

Mark S. Wrighton, Jeffrey M. Bolts, Andrew B. Bocarsly, Michael C. Palazzotto, and Erick G. Walton

J. Vac. Sci. Technol. 15, 1429 (1978); http://dx.doi.org/10.1116/1.569801 (7 pages) | Cited 5 times

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Semiconductor‐based photoelectrochemical cells for the conversion of light to electricity are described. Such cells consist of a semiconductor photoelectrode, a counterelectrode, and an electrolyte solution containing electroactive species. Results for cells employing certain n‐type II–VI (CdS, CdSe, CdTe) and III–V (GaP, GaAs, InP) photoelectrodes in solutions of electroactive X2−/Xn2−(X=S, Se, Te) species are reviewed. The key fact is that for a number of photoelectrode /X2−/Xn2− combinations we find that photoanodic decomposition of the semiconductor is virtually totally suppressed, allowing the sustained conversion of light to electricity. Preliminary results for n‐type Si photoelectrodes derivatized with electroactive ferrocene reagents are also outlined, and the associated photoelectrochemical activity of the surface species is compared to results for naked Si exposed to solutions of ferrocene.
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82.47.-a Applied electrochemistry
84.60.Ve Energy storage systems, including capacitor banks
73.40.Mr Semiconductor-electrolyte contacts

Abstract: Electrical properties of the Ga–GaAs interface immersed in electrolytic solutions

J. M. Woodall, C. Lanza, and J. L. Freeouf

J. Vac. Sci. Technol. 15, 1436 (1978); http://dx.doi.org/10.1116/1.569802 (1 page) | Cited 2 times

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Abstract Unavailable
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Mr Semiconductor-electrolyte contacts

Theoretical trends in the abrupt (110) AlAs–GaAs, Ge–GaAs, and Ge–ZnSe interfaces

Warren E. Pickett and Marvin L. Cohen

J. Vac. Sci. Technol. 15, 1437 (1978); http://dx.doi.org/10.1116/1.569803 (7 pages) | Cited 5 times

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The self‐consistent pseudopotential method has been applied to describe the electronic structure of the abrupt (110) interfaces of AlAs–GaAs, Ge–GaAs, and Ge–ZnSe system. These systems were chosen both for their technological interest as well as to study trends with ionicity. The method allows the study of existence, character, and density of interface states as well as allowing estimates of the conduction and valence‐band discontinuities and the characterization of the bonding properties of the interface. The results indicate that the ideal structure may be stable for AlAs–GaAs, but the character of the bonds at the Ge–GaAs and Ge–ZnSe interfaces suggest unbalanced forces on the atoms which will lead to relaxation. It is suggested that, in addition to the change of ionicity, the change of crystal symmetry (diamond–zincblende) across the interface may be of central importance in these systems.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Ge–GaAs(110) interface formation

R. S. Bauer and J. C. McMenamin

J. Vac. Sci. Technol. 15, 1444 (1978); http://dx.doi.org/10.1116/1.569804 (6 pages) | Cited 17 times

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The heterojunction chemistry for Ge grown by molecular beam epitaxy (MBE) on in situ cleaved GaAs exhibits significant interdiffusion in short times at growth temperatures TG of 430°C (significantly lower critical TG than that reported for moderate‐vacuum physical vapor deposition). This results in profound changes in the electronic properties of the interface as probed by synchrotron‐radiation‐excited 3d core electron photoemission. Even when there is significant alloying of the two lattice‐matched semiconductors, there is nearly equal probability for Ge to bond to either a Ga or an As atom at the initial stage. As Ge becomes the dominant species, we find As preferentially diffusing toward the Ge side of the junction. This As is distributed throughout the overlayer in contrast to metal–semiconductor interface formation where the diffusing constituent resides only on the free, growing surface. We show that these behaviors are consistent with the kinetic and thermodynamic properties of the atomic species. The valence band discontinuity is negligible over atomic dimensions, while for an abrupt interface (TG=350°C) we measure ΔEV=0.7±0.050.3 eV. The photoemission changes character rapidly with temperature, indicating an activation barrier for the diffusion below which simple expressions for attenuation of the photoelectrons by electron–electron scattering are applicable. In that case we deduce an escape depth of 7.0±0.5 Å, indicating uniform growth of Ge, with composition changing abruptly from GaAs over ∠1 bond length in the (110) direction. A negligible (<0.2 eV) localized interface dipole layer is formed in the process.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
81.65.-b Surface treatments

Abstract: Scattering‐theoretic approach to the electronic structure of semiconductor interfaces: The Ga‐terminated Ge–GaAs (100) interface

J. Pollmann and Sokrates T. Pantelides

J. Vac. Sci. Technol. 15, 1450 (1978); http://dx.doi.org/10.1116/1.569805 (1 page)

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Abstract Unavailable
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

XPS measurements of abrupt Ge–GaAs heterojunction interfaces

R. W. Grant, J. R. Waldrop, and E. A. Kraut

J. Vac. Sci. Technol. 15, 1451 (1978); http://dx.doi.org/10.1116/1.569806 (5 pages) | Cited 9 times

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A method has been developed to grow thin epitaxial layers of Ge on GaAs substrates within an XPS system by an evaporative MBE technique. Abrupt heterojunctions with Ge layer thicknesses of ?20 Å have been grown on (111), (110), and (100) GaAs crystal faces. By using XPS data obtained on these heterojunctions, variations in band gap discontinuities related to the crystallographic orientation dependence of interface dipoles have been observed directly. The data are also used to make an initial estimate of the valence band discontinuity for the abrupt Ge–GaAs heterojunction and with refinement of the technique, accurate values for this quantity should be obtainable.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.-i Photoemission and photoelectron spectra

Tight‐binding calculation for the AlAs–GaAs (100) interface

J. N. Schulman and T. C. McGill

J. Vac. Sci. Technol. 15, 1456 (1978); http://dx.doi.org/10.1116/1.569807 (3 pages) | Cited 1 time

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We report the results of a study of the electronic properties of the AlAs–GaAs interface using the tight‐binding method. The tight‐binding matrix for the superlattice system is used in the limit in which the thickness of the repeated superlattice slab becomes large. This system is studied in detail with special emphasis placed on the determination of interface states. No interface states with energies within the GaAs forbidden gap are found. The densities of states per layer are calculated and compared with bulk densities of states. They resemble the bulk densities of states except for layers adjacent to the interface.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Pseudopotential calculations for ultrathin layer heterostructures

Ed Caruthers and P. J. Lin‐Chung

J. Vac. Sci. Technol. 15, 1459 (1978); http://dx.doi.org/10.1116/1.569808 (6 pages) | Cited 5 times

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With molecular‐beam epitaxy it is possible to fabricate semiconductor heterostructures of the form (GaAs)m– (Ga1‐xAlxAs)n, 1?m, n?10, where m and n are the numbers of atomic layers of each kind of material in the alternating semiconductor regions. Energy bands of several of these structures have been calculated using new pseudopotentials for Ga, Al, and As. Band discontinuities, localized states, charge densities, and interface charge transfer have been found. Densities of states have also been calculated and the results indicate which kinds of experiments should give the best measure of disorder at the semiconducator–semiconductor interfaces in these heterostructures.
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71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
73.40.-c Electronic transport in interface structures
71.20.-b Electron density of states and band structure of crystalline solids
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Theoretical study of the orientation dependence of heterojunction energy band lineups

W. R. Frensley

J. Vac. Sci. Technol. 15, 1465 (1978); http://dx.doi.org/10.1116/1.569809 (4 pages) | Cited 1 time

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The orientation dependence of the energy band discontinuities at an abrupt heterojunction between lattice‐matched zincblende semiconductors is studied by modeling the microscopic charge distribuion near the heterojunction. The model includes both ionic and bond charges, and assumes that each chemical bond contributes independently to the total charge distribution. The energy band lineups are derived by calculating the interface dipole. The results indicate that there should be no difference in the band lineups for heterojuncions on (100) and (111) faces of similar polarity, and that the (110) lineup should be equal to the mean of the lineups for the A and B polar faces. The lineup should be completely independent of orientation for heterojunctions which have an element common to both semiconductors, such as GaAs–AlAs. Any difference in band lineup between heterojunctions on nonpolar (110) planes and those on the (100) or (111) planes is related to deviations of the bond parameters from chemically systematic behavior, and thus is expected to be small.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions

Abstract: Characterization of defects in quaternary III–V heterojunctions by x‐ray techniques

M. Sauvage and J. F. Petroff

J. Vac. Sci. Technol. 15, 1469 (1978); http://dx.doi.org/10.1116/1.569810 (1 page)

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Abstract Unavailable
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.05.C- X-ray diffraction and scattering
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Abstract: Effect of lattice‐mismatch stress on the energy band gap and latice parameter of III‐V heteroepitaxial layers

G. H. Olsen, C. J. Nuese, and R. T. Smith

J. Vac. Sci. Technol. 15, 1470 (1978); http://dx.doi.org/10.1116/1.569811 (1 page)

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Abstract Unavailable
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.35.Gy Mechanical properties; surface strains
68.35.Iv Acoustical properties
73.20.-r Electron states at surfaces and interfaces

Effect of interface recombination at AlxGa1−xAs p–n junction perimeters on photoluminescence and current

C. H. Henry and R. A. Logan

J. Vac. Sci. Technol. 15, 1471 (1978); http://dx.doi.org/10.1116/1.569767 (4 pages) | Cited 7 times

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The interfaces forming the perimeters of AlxGa1−xAs p–n junctions, such as cleaved surfaces or etched surfaces are regions of intense nonradiative recombination. Almost all of the p–n junction 2kT current is due to recombination at these nonradiative perimeters. When an uncontacted sample is studied in photoluminescence, these interfaces produce broad nonradiative regions known as large dark spots. The rate of interface recombination can be quantitatively evaluated from measurement of either the 2kT current or the large dark spot line shape. The 2kT current is usually explained in terms of the Sah, Noyce, and Shockley model of p–n depletion layer recombination. We develop an alternative model in which we show that recombination at a depleted surface will have 2kT charater. The rate of surface recombination is R=s0(np)1/2=s0ni exp(eV/2kT) where s0?4×105 cm s−1 for x=0.08 active layers with etched surfaces. This form of the recombination rate follows naturally from the requirement that the interface remain neutral.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
78.60.Fi Electroluminescence

Interfacial recombination in GaAlAs–GaAs heterostructures

R. J. Nelson

J. Vac. Sci. Technol. 15, 1475 (1978); http://dx.doi.org/10.1116/1.569768 (3 pages) | Cited 13 times

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Photoluminescence time‐decay measurements (300 K) are reported for Ga0.5Al0.5As–GaAs double heterostructures over a wide range of GaAs active layer thickness and doping levels. Decay times range from 10 to 650 ns in variously doped GaAs samples. Effects of self‐absorption of luminescence and doping level on the decay times are observed for GaAs layer thickness d≳1 μm. For sufficiently thin GaAs layers, interfacial recombination is believed to determine the decay time. The interfacial recombination velocity is observed to vary from Si=300 cm s−1 for p=5×1015 cm−3 heterostructures to Si=500 cm s−1 for p=1.7×1017 cm−3.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.40.Fy Semiconductors
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Abstract: Superfine heterostructures of In1−xGaxAs and GaSb1−YAsY

L. L. Chang

J. Vac. Sci. Technol. 15, 1478 (1978); http://dx.doi.org/10.1116/1.569769 (2 pages) | Cited 3 times

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Abstract Unavailable
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Auger profiling studies of LPE n‐AlxGa1−xAs–n‐GaAs heterojunctions and the absence of rectification

C. M. Garner, Y. D. Shen, C. Y. Su, G. L. Pearson, and W. E. Spicer

J. Vac. Sci. Technol. 15, 1480 (1978); http://dx.doi.org/10.1116/1.569770 (3 pages) | Cited 5 times

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Grading of the heterojunction interface has previously been proposed to explain the absence of rectification for LPE n–n heterojunctions. In this study, Auger profiles were made of LPE n‐AlxGa1−xAs–n‐GaAs (doped 1015 to 1016 cm−3 in both layers) which had been grown to minimize any barrier lowering due to the grading width and high carrier concentration. In a specific case, the calculated interface widths necessary to eliminate the barrier was greater than 500 Å; however, the measured interface width was less than 150 Å. Ion profiling effects such as preferential sputtering, knock‐on, and substrate surface roughness would only increase the measured interface width. Although the measured interface width was much less than that required by theory to remove the barrier in the conduction band, the samples did not exhibit rectification. This indicates that the present grading model may be insufficient to explain the lack of rectification of these samples.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Field‐assisted minority carrier electron transport across a p‐InGaAs/p‐InP heterojunction

P. E. Gregory, J. S. Escher, S. B. Hyder, Y. M. Houng, and G. A. Antypas

J. Vac. Sci. Technol. 15, 1483 (1978); http://dx.doi.org/10.1116/1.569771 (5 pages) | Cited 9 times

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A field‐assisted photocathode has been made which has a reflection yield quantum efficiency of ∠1% out to a wavelength of 1.6 μ. The cathode is a heterojuncation InP/InGaAs/InP structure fabricated by a hybrid VPE/LPE process. Photoelectrons generated for wavelengths ?1 μm must cross a p‐InP/p‐InGaAs heterojunction, under bias. To achieve high transfer across the p–p heterojunction, the heterojunction must be carefully lattice matched, the InP emitter must be ?1 μm thick and have p‐type doping in the low 1015 cm−3 range, the InGaAs layer must have doping in the low 1016 cm−3 range, and the heterojunction composition grading distance must be ?1000 Å. These criteria are all met by the VPE/LPE grown heterojunction. Heterojunction transfer efficiencies approaching 100% for bias voltages 3–5 V have been measured.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Ha Photomultipliers; phototubes and photocathodes

Optical studies of the anodic oxide on GaAs

E. D. Palik, N. Ginsburg, R. T. Holm, and J. W. Gibson

J. Vac. Sci. Technol. 15, 1488 (1978); http://dx.doi.org/10.1116/1.569772 (10 pages) | Cited 7 times

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Reflection and transmission measurements of an anodic‐oxide film grown on GaAs have been carried out from 0.01 to 6 eV (100 to 48 000 cm−1). The dispersion in the index of refraction has been determined in the high‐frequency range from an analysis of reflection interference fringes. The ir reflection and transmission spectra of crystalline arsenolite, amorphous As2O3, polycrystalline β‐Ga2O3, and amorphous Ga2O3 have been measured and compared with the anodic‐oxide spectrum. In the anodic oxide, three vibration bands at 305, 600, and 800 cm−1 have been found and two bands at 350 and 550 cm−1 have been inferred, all of which can be assigned to the arsenic‐oxide and gallium‐oxide constituents of the film. Lines assigned to arsenic oxide in the anodic oxide have much broader widths than the corresponding lines in amorphous arsenic oxide. The anodic‐oxide bands are analyzed to determine their contribution to the dc dielectric constant.
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75.20.Ck Nonmetals

Perspectives on III–V compound MIS structures

H. H. Wieder

J. Vac. Sci. Technol. 15, 1498 (1978); http://dx.doi.org/10.1116/1.569773 (9 pages) | Cited 32 times

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An overview and assessment is provided of some aspects of the physics and technology of InP, GaAs, InAs, and InSb MIS structures with homomorphic and heteromorphic dielectric layers. Experimental measurements made on such InP and InSb MIS structures are interpreted in the context of the experimental and theoretical framework developed for the Si–SiOx MOS system. GaAs and InAs MIS structure exhibit anomalies attributed principally to pinning of the Fermi level by extrinsic surface states near midgap for GaAs and within the conduction band for InAs. Microwave power gain can be obtained from InP and GaAs MIS field effect transistors irrespective of the density of fast surface states present in them; the surface states cannot respond to the μ‐wave signals applied to the MISFET gates.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices

Abstract: Dynamic properties of interface states in MOS structures

M. Schulz

J. Vac. Sci. Technol. 15, 1507 (1978); http://dx.doi.org/10.1116/1.569774 (1 page)

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Abstract Unavailable
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Transient capacitance in GaAs and InP MOS capacitors

J. Stannard

J. Vac. Sci. Technol. 15, 1508 (1978); http://dx.doi.org/10.1116/1.569775 (5 pages) | Cited 4 times

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Capacitance–voltage and transient capacitance measurements were made on MOS capacitors fabricated on bulk n‐type GaAs using anodic oxidation. Similar measurements were made on InP–SiO2 capacitors fabricated on bulk n‐type InP. The InP structure shows much less charge buildup at the interface upon cooling. A transient response with a new signature (Ec−0.08 eV, 8×10−22 cm2) was observed in GaAs, and previously observed bulk center in InP was also characterized (Ec−0.18 eV, σ−e=6.5×10−15 cm2). A deep center associated with radiation damage appeared prominently in the transient response of the GaAs–anodic‐oxide capacitor. Clear evidence was obtained in the InP–SiO2 capacitors of a transient response which has the properties expected of interface states. This response was not observed in GaAs because of high surface fields.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
78.40.Fy Semiconductors

Analysis of the oxide/semiconductor interface using Auger and ESCA as applied to InP and GaAs

C. W. Wilmsen and R. W. Kee

J. Vac. Sci. Technol. 15, 1513 (1978); http://dx.doi.org/10.1116/1.569776 (5 pages) | Cited 27 times

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This paper compares the Auger and ESCA techniques used to characterize the interfaces of thermally grown and anodic oxides of InP and GaAs. In the anodic oxide of GaAs, the Ga–O bonding extends deeper into the GaAs than the As–O bonding. In the anodic oxide of InP, both the P–O and In–O bonding penetrate to the same depth. The anodic oxide–GaAs interface changes with electrolyte. There is elemental P at the interface of the thermal oxide on InP, but it was not possible to prove or disprove the existence of elemental As at the anodic oxide/GaAs interface. It was found that the ESCA technique provided much needed bonding information which greatly facilitates characterizing the interface. It appears essential that both composition and bonding be determined.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Abstract: Chemical structure of the transitional region of the SiO2–Si interface

F. J. Grunthaner and J. Maserjian

J. Vac. Sci. Technol. 15, 1518 (1978); http://dx.doi.org/10.1116/1.569777 (1 page) | Cited 2 times

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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.-b Surface treatments

Abstract: Auger–sputter profiling study of phosphorus pileup at the Si–SiO2 interface

S. A. Schwarz, C. R. Helms, W. E. Spicer, and N. J. Taylor

J. Vac. Sci. Technol. 15, 1519 (1978); http://dx.doi.org/10.1116/1.569778 (1 page) | Cited 1 time

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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Interface characteristics of thermal Si02 on SiC

R. W. Kee, K. M. Geib, C. W. Wilmsen, and D. K. Ferry

J. Vac. Sci. Technol. 15, 1520 (1978); http://dx.doi.org/10.1116/1.569779 (4 pages) | Cited 14 times

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The interface between a thermally grown silicon dioxide and a vapor epitaxial layer of cubic silicon carbide has been investigated. Initial studies have concentrated on an Auger analysis of the interface region. The interface region is considerably wider for the unannealed oxide than that between Si and Si02. The Si KLL peak shift occurs over a region of some 130 Å, while the compositional profile indicates a transition region about 210 Å wide. No buildup of free carbon is found at the interface. The Si KLL peak changes indicate that the interface is composed primarily of Si02 and SiC. The cause of the wide interface is discussed in terms of the reaction products of carbon.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Abstract: Properties of plasma‐oxidized GaAs films

A. J. Polak, R. P. H. Chang, C. C. Chang, and T. T. Sheng

J. Vac. Sci. Technol. 15, 1524 (1978); http://dx.doi.org/10.1116/1.569780 (1 page)

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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors

Plasma anodization of GaAs in a dc discharge

L. A. Chesler and G. Y. Robinson

J. Vac. Sci. Technol. 15, 1525 (1978); http://dx.doi.org/10.1116/1.569781 (5 pages) | Cited 8 times

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Thin oxide films have been grown by anodization of GaAs in the negative glow region of a dc oxygen discharge. As‐grown and annealed films grown on both p‐ and n‐type bulk GaAs were characterized by conventional electrical measurements and by Auger analysis. The anodic oxide displayed ohmic characteristics up to fields of 0.5×106 V/cm with a resistivity of 1014 Ω cm in the as‐grown condition and over 1015 Ω cm after anneal. Capacitance–voltage measurements indicated a fixed positive charge in the insulator of 1.5×1012 cm−2 for p‐type substrates and 4.0×1011 cm−2 for n‐type substrates. Majority carrier trapping near the oxide/GaAs interface was reduced by annealing and a corresponding reduction of As at the interface was observed. The distribution of fast interface states on p‐type substrates had a broad minimum of 7–10×1011 cm−2 eV−1 near midgap while the distribution of fast interface states displayed a peak of over 1013 cm−2 eV−1 near midgap on n‐type samples. No corresponding difference in the Auger composition profiles were observed between n‐ and p‐type samples.
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81.15.Cd Deposition by sputtering

Tight‐binding study of the electronic structure of the InAs–GaSb (001) superlattice

R. N. Nucho and A. Madhukar

J. Vac. Sci. Technol. 15, 1530 (1978); http://dx.doi.org/10.1116/1.569782 (5 pages) | Cited 5 times

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We present tight‐binding model calculations for the InAs–GaSb (001) superlattice including second nearest‐neighbor interactions. The tight‐binding parameters used were obtained by fitting to the bulk band structure of InAs, GaSb, InSb, and GaAs. The parameters were required to be consistent with each other, to yield accurate energy values at the symmetry points, and to reproduce well the overall dispersion. Results for the behavior of the energy gap of the superlattice as a funcion of layer thickness, and of the conduction‐band–valence‐band edge discontinuity at the Γ point have been obtained. With increasing magnitude of the discontinuity, the nature of the superlattice changes from a direct gap semiconductor to an indirect gap semiconductor, to a semimetal. These results are compared with recent experimental studies.
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71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Sheet resistance variation on color‐banded silicon following high dose implantations at high dose rates

D. G. Beanland and D. J. Chivers

J. Vac. Sci. Technol. 15, 1536 (1978); http://dx.doi.org/10.1116/1.569783 (5 pages) | Cited 2 times

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With some scanning systems color bands are produced on silicon wafers after high dose implantation. The color bands arise from the amorphous zones within the silicon and the thickness of these zones is determined by the temperature attained by the wafer during implantation. The sheet resistance of ’’color‐banded’’ silicon wafers has been measured following a series of isochronal anneals and found to vary considerably across a wafer, in a manner correlated with the color bands. The sheet resistance variation persists through a series of isochronal anneals to 1100°C, although it is reduced in magnitude. The implications for high dose implantation of silicon wafers are briefly discussed.
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61.72.U- Doping and impurity implantation
61.80.Jh Ion radiation effects

Surface composition of polycrystalline Au–Cu alloys as a function of temperature

Wolfgang Losch and Jürgen Kirschner

J. Vac. Sci. Technol. 15, 1541 (1978); http://dx.doi.org/10.1116/1.569784 (8 pages) | Cited 4 times

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The surface composition of polycrystalline Au–Cu alloys is studied by means of Auger electron spectroscopy (AES) in the composition range from 7.5 to 56.3 at. % Au. Well equilibrated surfaces show predominant Au segregation in the temperature range from 200° to 550°C as observed by the low‐energy Cu (58/60 eV) and Au (66/69 eV) Auger transitions. The Au segregation decreases linearly with increasing temperature. Quantitative evaluation, based on internal and external calibration shows Au enrichment up to 100%. The deeper layers, studied by means of the high‐energy Cu (920 eV) and Au (2024 eV) Auger transitions, generally do not show Au but Cu enrichment. This result is consistent with depth profiling by Ar+ sputtering. Segregation of S or O impurities at T?600°C leads to strong, chemically induced Cu enrichment on the surface as identified by the appearance of fine structure in the sulfur Auger transition. Current theories of segregation for pure alloys are discussed. Lowering of surface and lattice distortion energy are found to be important, whereas the heat of sublimation has no influence on segregation in Au–Cu alloys.
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79.20.Fv Electron impact: Auger emission
68.35.Md Surface thermodynamics, surface energies

Alloy compositional profiles by AES, ESCA, and ion sputtering: Air‐exposed Fe1−xPdx films

Wen‐Yaung Lee, M. H. Lee, and Jerome M. Eldridge

J. Vac. Sci. Technol. 15, 1549 (1978); http://dx.doi.org/10.1116/1.569785 (5 pages) | Cited 2 times

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Surface studies of air‐exposed, 1000 Å‐thick Fe1−xPdx alloy films with x=0.06–0.74 were carried out using AES, ESCA, and in situ ion sputtering techniques. It was found that Fe is preferentially oxidized on the surface with a Pd‐enriched region formed underneath the oxide layer. The iron oxide thickness decreases linearly as the Pd concentration is increased, becoming quite small for x≳0.6. Fe2O3 is the dominant oxidation product for the lower Pd concentration alloys while Fe3O4 appears to be the major oxide for x≳0.36. The steady state composition of the surfaces measured both by AES and ESCA techniques afer prolonged sputtering also indicated that the relative Pd‐to‐Fe sputtering yield remains constant for films with x between 0.06 and ∠0.38 and decreases to another constant value for films with larger x values. No preferential sputtering is observed in the AES case for alloys with x≳0.38, if the atomic density is taken into account; for x<0.38, Pd sputters about twice as fast as Fe. In the ESCA case, very strong preferential sputtering of Pd to Fe is observed. Possible origins for this sputtering yield change, including the phase transition and the residual oxygen content of the alloy, are discussed.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Design and optimization of directly heated LaB6 cathode assemblies for electron‐beam instruments

P. H. Schmidt, L. D. Longinotti, D. C. Joy, S. D. Ferris, H. J. Leamy, and Z. Fisk

J. Vac. Sci. Technol. 15, 1554 (1978); http://dx.doi.org/10.1116/1.569786 (7 pages) | Cited 9 times

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A description is given of the design and testing of a directly heated, stable, electron source utilizing a single‐crystal lanthanum hexaboride (LaB6) cathode. The emitter mounting fixture consists of an adjustable molybdenum base unit supported on gas‐impervious alumina or machinable glass. Single‐crystal cathode rods are securely clamped and positioned between vitreous carbon jaws that are resistively heated. The complete assembly is designed to be a direct ’’plug‐in’’ substitute for the conventional tungsten thermionic filaments used in electron‐beam instruments. The cathode current density for 〈110〉 axial orientations is found to be ten times higher than that for 〈100〉 orientations under equivalent conditions, a value of 50 A cm−2 being measured at 1500°C with an observed lifetime in excess of 300 h. Optimum vacuum conditions for high lifetime and stable operation are in the range 1×10−6 Torr and lower. Comparison values for the emission at various temperatures from other borides, and tungsten, are also given.
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79.40.+z Thermionic emission
81.70.-q Methods of materials testing and analysis
29.25.Bx Electron sources

Method for the cross‐sectional examination of molecular semiconductor/metal film junctions using transmission electron microscopy

William Katz, C. A. Evans, David R. Eaton, and Larry R. Faulkner

J. Vac. Sci. Technol. 15, 1561 (1978); http://dx.doi.org/10.1116/1.569787 (4 pages) | Cited 1 time

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Junctions between thin films of metals and molecular semiconductors are of current interest for their uses in electrochemistry and in photovoltaic devices. Characteristics such as interdiffusion, interfacial structure, and pinhole formation are important for various applications. A method has been developed for microstructural characterization of these junctions by the examination of thin cross sections using transmission electron microscopy (TEM). This method incorporates preparation techniques that are commonly used for both inorganic and biological samples. The thin‐film system is vapor deposited onto an epoxy medium, then a second epoxy layer is added, so that one obtains a ’’sandwich’’ arrangement, in which the thin‐film system is wholly contained within the rigid epoxy casting. A typical system is zinc phthalocyanine (ZnPc) placed between two gold or silver layers. The whole sandwich casting is then cross sectioned by ultramicrotomy. Results concerning the interfacial morphology, obtained by TEM examination of the thin sections, seem to indicate a sharp interface with no bulk diffusion of one material into the other. However, both the metal and the ZnPc seem to exhibit significant surface mobility during deposition when the substrate is held at room temperature. Pinholes formed in the ZnPc were filled with the metal and formed shorts between the two metal layers. This phenomenon is explained and interpreted.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
82.80.-d Chemical analysis and related physical methods of analysis

Two‐step process for thin films of tin dioxide

Anant G. Sabnis

J. Vac. Sci. Technol. 15, 1565 (1978); http://dx.doi.org/10.1116/1.569788 (3 pages) | Cited 5 times

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A two‐step process for deposition of thin films of tin dioxide is described. The first step consists of depositing opaque films of oxygen deficient tin dioxide by dc sputtering of porous targets in an argon atmosphere; the second step is to oxidize the films at 400 °C in air. The target, which is used in this research, contains 80% SnO2 and 20% Sb by weight. Its density is about 60%–70% of the solid density of SnO2. The films have been heated in air at different temperatures. The variations in conductivity, transparency, and thickness with heating temperature and duration are presented. The stability and annealing behavior of the films are discussed. It seems possible to control the film conductivity by controlling heating time. The films, at the end of 6 h of heating at 400 °C in air, have conductivity of about 2Ω−1 cm−1 and transparency of about 80%.
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81.15.Cd Deposition by sputtering
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Self‐maintaining high‐voltage ac vacuum system

Elizabeth E. Ames, Peter Graneau, and M. B. Silevitch

J. Vac. Sci. Technol. 15, 1568 (1978); http://dx.doi.org/10.1116/1.569812 (4 pages)

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This paper describes an experimental investigation of pumping characteristics of high‐voltage ac Penning discharges. The investigation has focused on maintaining a vacuum in the 10−5 Torr pressure range while operating at a high ac voltage in the 10–100 kV rms range. It is intended that the pump will be an integral part of high‐voltage ac power equipment and will thus ’’self‐maintain’’ a vacuum in the equipment.
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07.30.Cy Vacuum pumps
52.80.Sm Magnetoactive discharges (e.g., Penning discharges)

Scale‐up problems in electron‐beam evaporation and sputtering

John L. Hughes

J. Vac. Sci. Technol. 15, 1572 (1978); http://dx.doi.org/10.1116/1.569813 (8 pages)

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A variety of problems are encountered in the scale‐up of electron‐beam evaporation and sputtering processes from bell jar experiments to production processes. These problems include greatly altered outgassing characteristics, the effects of substrate motion, residual gas pressure and deposition rates. The overall efficiencies with which substrates can collect condensing vapor and the energy efficiency of electron beam and sputtering vaporization processes are also significant with respect to reliable production coater designs. Specific considerations and problems are examined with respect to actual processes which have been scaled‐up, both successfully and unsuccessfully.
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81.10.Bk Growth from vapor
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.90.+c Other topics in materials science (restricted to new topics in section 81)

Synchrotron radiation photoemission studies of the adsorption of oxygen on magnesium and aluminium

D. Norman and D. P. Woodruff

J. Vac. Sci. Technol. 15, 1580 (1978); http://dx.doi.org/10.1116/1.569814 (6 pages) | Cited 1 time

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The sorption of oxygen on polycrystalline films of Mg and Al has been studied by photoemission using synchrotron radiation in the photon energy range 70–150 eV. The 2p levels, situated 50.0 eV (Mg) and 72.8 eV (Al) below the Fermi level in the clean metals, shift to higher binding energy by 1.3 (Mg) and 2.6 eV (Al) on heavy oxidation. There is some evidence of a smaller shift, corresponding to a chemisorbed state, coexistent with the oxide peak. For oxygen on magnesium, an interatomic Auger transition, as previously reported from electron‐stimulated Auger electron measurements, was observed for a wide range of exposures. An O 2p valence‐band resonance is seen 6.1 (Mg) and 7.1 eV (Al) below the Fermi level, with accompanying shoulders 2.6 eV deeper in both systems. Oxidation also produces a marked increase in the total 2p emission from the metallic species, which we attribute to a longer electron mean free path in the oxide than in the metal. The ratio of the mean free path in oxide and metal is typically a factor of 2 for both Mg and Al, and this ratio is energy dependent.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.40.-c Electronic transport in interface structures
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Desorption of neutral molecules from Al(6061) by electron and ion bombardment

D. Edwards

J. Vac. Sci. Technol. 15, 1586 (1978); http://dx.doi.org/10.1116/1.569815 (11 pages) | Cited 2 times

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The desorption of neutral molecules by ion (1000‐eV Ar+) and electron (500 eV) impact on aluminum 6061 surfaces is reported. The molecular desorption yields are determined for the following aluminum treatments: (1) samples prepared with nominally the same laboratory treatments; (2) two types of wet chemistry treatments; (3) various in situ gas exposures (including HC1, C12); (4) glow discharge treatments. In summary, it is found that the various prevacuum treatments have little influence on the desorption yields whereas the in situ Cl2 exposure markedly reduces both the ion and electron desorption yields. In addition, the unit yield energy, E0, is also measured for the above sample conditionings. It is similarly found that neither the prevacuum sample conditionings nor the in situ gas exposures (with the exception of Cl2) affect E0 by more than 10% whereas the in situ Cl2 exposure (1 atm, 10 min) increases E0 by a factor of 2 and provides an example illustrating the possible utility of an in situ chemical treatment for the conditioning of vacuum surfaces of large‐scale devices.
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79.20.Kz Other electron-impact emission phenomena
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
81.05.Bx Metals, semimetals, and alloys

Mean free path of negative ions in diode sputtering

J. M. E. Harper, J. J. Cuomo, R. J. Gambino, H. R. Kaufman, and R. S. Robinson

J. Vac. Sci. Technol. 15, 1597 (1978); http://dx.doi.org/10.1116/1.569816 (4 pages) | Cited 8 times

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Negative ions produced in the sputtering of certain compounds (e.g., SmAu, EuAu, CsAu, and LaF3) are capable of dominating the film‐growth process in a thin‐film depostion system. Under some conditions sputter etching of substrates is observed due to a high flux of negative ions accelerated from the target surface. The energy and collimation of these negative ions are examined by evaluating the cross sections for electron detachment and directed momentum loss. Under typical sputtering conditions the negative ions are found to retain their charge long enough to accelerate to the full dark space voltage. The mean free path at this energy is estimated from the Ar–Ar interaction potential and found to be many times longer than the thermal mean free path. These results explain the sharply outlined region of substrate etching by the negative ion flux and lead to a picture of a highly collimated, energetic particle beam directed away from the target surface. negative ion flux and lead to a picture of a highly collimated,
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

New sputtering system for manufacturing ZnO thin‐film SAW Devices

Kenzo Ohji, Osamu Yamazaki, Kiyotaka Wasa, and Shigeru Hayakawa

J. Vac. Sci. Technol. 15, 1601 (1978); http://dx.doi.org/10.1116/1.569817 (4 pages) | Cited 5 times

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An improved rf sputtering system for manufacturing ZnO thin‐film devices is described. The system consists of a hemispherical electrode geometry with a ZnO center cathode and provides c axis highly oriented ZnO films onto 60 sheets of glass substrate wafers of 25 mm square in one sputtering run. The growth rate of ZnO films is 0.3–0.7 μm/h. The film thickness variations in these wafers are within ±1%. The electrical resistivity of the films ρ?106–107 Ω cm, dielectric constant ϵ∗?8.5, the electromechanical coupling in a longitudinal mode kt?0.23–0.24, in a Rayleigh mode keff?0.07–0.085 for the ZnO film thickness of 3% of the wavelength. The present system enables the manufacture of the ZnO thin‐film SAW filter with a frequency accuracy, better than ±0.1%, and a temperature stability, better than −10 ppm/°C.
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81.10.Bk Growth from vapor
81.15.Cd Deposition by sputtering
84.30.Vn Filters
68.35.Gy Mechanical properties; surface strains
68.35.Iv Acoustical properties

rf induction technique for sample heating in surface science experiments

Harold F. Winters, Joe Schlaegel, and Don Horne

J. Vac. Sci. Technol. 15, 1605 (1978); http://dx.doi.org/10.1116/1.569818 (4 pages) | Cited 5 times

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An rf induction technique, which can be used to heat most samples used in surface science experiments, is described in detail. It is shown that the technique (1) can rapidly produce high temperature (2500 K), (2) produces uniform temperature over the surface, (3) produces minimal outgassing, (4) is independent of sample shape, (5) is mechanically simple, (6) is ideal for sequentially heating a number of samples, and (7) is compatible with the types of vacuum systems often used by investigators in the field of surface science. Design and construction techniques are described with special emphasis placed on potential problems.
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81.65.-b Surface treatments
81.70.-q Methods of materials testing and analysis

First intercontinental test of UHV transfer device

J. P. Hobson

J. Vac. Sci. Technol. 15, 1609 (1978); http://dx.doi.org/10.1116/1.569819 (3 pages) | Cited 4 times

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Abstract Unavailable
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07.30.Hd Vacuum testing methods; leak detectors
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