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May 2013

Volume 31, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

J. Vac. Sci. Technol. B 31, 03C110 (2013); http://dx.doi.org/10.1116/1.4793476 (4 pages)

Supanee Sukrittanon, YanJin Kuang (邝彦瑾), and Charles W. Tu
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Insight into the multicomponent nature of negative bias temperature instability

Duc D. Nguyen, Camron Kouhestani, Kenneth E. Kambour, and Roderick A. B. Devine

J. Vac. Sci. Technol. B 31, 030601 (2013); http://dx.doi.org/10.1116/1.4796115 (4 pages)

Online Publication Date: 22 March 2013

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A novel measurement technique is used to extract two physically distinct “permanent” (long lived on our experimental time scale, ≤12 000 s) and one recoverable charge components of the negative bias temperature instability in p-channel metal–oxide–semiconductor field effect transistors under inversion and n-channel devices under accumulation. The results suggest that the permanent components are present in both cases, while there is little, if any, recoverable charge present in the case of the n-channel device. A physical explanation is provided involving the band energy diagram to explain these observations.
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85.30.Tv Field effect devices

Enhanced response to molecular adsorption of structurally defective graphene

Kanghyun Kim, Haeyong Kang, Cho Yeon Lee, and Wan Soo Yun

J. Vac. Sci. Technol. B 31, 030602 (2013); http://dx.doi.org/10.1116/1.4798649 (5 pages)

Online Publication Date: 5 April 2013

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This study shows that a minimal introduction of structural defects to graphene can greatly enhance its sensitivity to molecular gas adsorption. The electrical conductance of graphene is enhanced by several orders of magnitude after defect generation by exposure to Ar plasma for just a few seconds. This enhancement in the response of the graphene is strongly dependent upon the extent of the defect site formation, reflecting the dominant effect of the defects on graphene's physicochemical sensitivity to molecular adsorption. Repeated cycles of the adsorption and desorption of gas molecules on the same graphene device are successfully demonstrated, implying the promise of the graphene device as a molecular sensing platform.
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68.43.Mn Adsorption kinetics
61.48.Gh Structure of graphene
73.61.Wp Fullerenes and related materials

Coexistence of weak ferromagnetism and polar lattice distortion in epitaxial NiTiO3 thin films of the LiNbO3-type structure

Tamas Varga, Timothy C. Droubay, Mark E. Bowden, Robert J. Colby, Sandeep Manandhar, Vaithiyalingam Shutthanandan, Dehong Hu, Bernd C. Kabius, Edoardo Apra, William A. Shelton, and Scott A. Chambers

J. Vac. Sci. Technol. B 31, 030603 (2013); http://dx.doi.org/10.1116/1.4801664 (5 pages)

Online Publication Date: 15 April 2013

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The authors report the magnetic and structural characteristics of epitaxial NiTiO3 films grown by pulsed laser deposition that are isostructural with acentric LiNbO3 (space group R3c). Optical second harmonic generation and magnetometry demonstrate lattice polarization at room temperature and weak ferromagnetism below 250 K, respectively. These results appear to be consistent with earlier predictions from first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in a series of transition metal titanates crystallizing in the LiNbO3 structure. This acentric form of NiTiO3 is believed to be one of the rare examples of ferroelectrics exhibiting weak ferromagnetism generated by a Dzyaloshinskii–Moriya interaction.
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75.30.-m Intrinsic properties of magnetically ordered materials
77.55.Nv Multiferroic/magnetoelectric films
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
75.70.Ak Magnetic properties of monolayers and thin films

New method for determining flat-band voltage in high mobility semiconductors

Roy Winter, Jaesoo Ahn, Paul C. McIntyre, and Moshe Eizenberg

J. Vac. Sci. Technol. B 31, 030604 (2013); http://dx.doi.org/10.1116/1.4802478 (4 pages)

Online Publication Date: 18 April 2013

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The method that is commonly used for determining the flat-band voltage (VFB) and the flat-band capacitance (CFB) of metal oxide semiconductor (MOS) capacitors depends on many parameters and can only be used in the case of low interface trap density (Dit) when the capacitance–voltage measurements are carried out at high frequencies. This paper demonstrates a new and simple method for determining VFB and CFB. The method is based on the point of inflection in the capacitance–voltage curve. This method does not require the knowledge of material or experimental parameters and can be used on high Dit and high border trap density MOS structures at all frequencies.
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84.32.Tt Capacitors

Improvement of zirconium-doped hafnium oxide high-k dielectric properties by adding molybdenum

Chi-Chou Lin and Yue Kuo

J. Vac. Sci. Technol. B 31, 030605 (2013); http://dx.doi.org/10.1116/1.4802778 (5 pages)

Online Publication Date: 23 April 2013

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Dielectric properties of the Zr-doped hafnium oxide high-k thin film were improved with the addition of a small amount of molybdenum. The addition of molybdenum reduced the interface density of states and the oxide charge trapping density due to the removal of some oxygen vacancies and Hf dangling bonds in the film. It also decreased the leakage current and increased the breakdown voltage because of the increase of the total film thickness. The barrier height between the gate electrode and the high-k film was lowered as a result of the formation of a dipole layer at the interface. Therefore, the addition of a small amount of metal is an effective method to improve the dielectric properties of the high-k film.
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77.55.D- High-permittivity gate dielectric films
77.22.Jp Dielectric breakdown and space-charge effects
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Preparation of a clean Ge(001) surface using oxygen plasma cleaning

Patrick Ponath, Agham B. Posadas, Richard C. Hatch, and Alexander A. Demkov

J. Vac. Sci. Technol. B 31, 031201 (2013); http://dx.doi.org/10.1116/1.4798390 (5 pages)

Online Publication Date: 3 April 2013

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The authors demonstrate a method to obtain a clean and smooth Ge (001) surface using oxygen plasma cleaning without sputtering or Ge regrowth. The preparation of the germanium surface consists of four cycles of ex situ wet etching using hydrochloric acid as the etchant and H2O2 as the oxidant. Subsequently, the sample is outgassed and exposed to an oxygen plasma for 30 min followed by thermal desorption of the newly formed oxide layer. Reflection high-energy electron diffraction shows a clear 2 × 1 reconstruction of the germanium surface. In situ x-ray photoelectron spectroscopy measurements confirm that the cleaned surface is free of carbon contamination and that no GeO2 remains. Angle-resolved photoemission spectra of the cleaned Ge show the peak associated with the Ge surface state indicating a very clean surface. Atomic force microscope images further indicate a smooth germanium surface with a mean surface roughness of approximately 3 Å after plasma cleaning.
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81.65.Cf Surface cleaning, etching, patterning
68.35.bg Semiconductors
68.43.Nr Desorption kinetics
52.77.Bn Etching and cleaning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.05.Cy Elemental semiconductors

Direct integration of subwavelength structure on a GaAs solar cell by using colloidal lithography and dry etching process

Dae-Seon Kim, Sung-Hwa Eo, and Jae-Hyung Jang

J. Vac. Sci. Technol. B 31, 031202 (2013); http://dx.doi.org/10.1116/1.4798410 (5 pages)

Online Publication Date: 4 April 2013

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An antireflective subwavelength structure (SWS) was realized on the InGaP layer of a GaAs solar cell by using colloidal lithography followed by dry etching process. The fabricated SWS with an aspect ratio of 1.33 and a period of 300 nm showed enhanced optical properties and device characteristics. The average reflectance of the SWS surface of the GaAs solar cell was 7.1% in the wavelength range between 300 and 1000 nm. More solar energy was absorbed by the GaAs solar cell due to the lowered surface reflection by the SWS. It is the dominant factor in the 28.2% improvement of the power-conversion efficiency (η) of the SWS-integrated GaAs solar cell as compared to that of the GaAs solar cells without SWS.
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88.40.jm Thin film III-V and II-VI based solar cells
88.40.hj Efficiency and performance of solar cells

Effects of catalyst thickness on the fabrication and performance of carbon nanotube-templated thin layer chromatography plates

Supriya S. Kanyal, David S. Jensen, Andrew J. Miles, Andrew E. Dadson, Michael A. Vail, Rebecca Olsen, Fabien Scorza, Judy Nichols, Richard R. Vanfleet, Robert C. Davis, and Matthew R. Linford

J. Vac. Sci. Technol. B 31, 031203 (2013); http://dx.doi.org/10.1116/1.4795859 (8 pages) | Cited 1 time

Online Publication Date: 5 April 2013

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The effects of iron catalyst thickness on the fabrication and performance of microfabricated, binder-free, carbon nanotube (CNT)-templated, thin layer chromatography (TLC) plates are demonstrated. The iron catalyst was deposited at thicknesses ranging from 4 to 18 nm in increments of 2 nm. Its thickness plays a key role in governing the integrity and separation capabilities of microfabricated TLC plates, as determined using a test dye mixture. Atomic force microscopy and scanning electron microscopy show that smaller and more numerous catalyst nanoparticles are formed from thinner Fe layers, which in turn govern the diameters and densities of the CNTs. The average diameter of the Fe nanoparticles, Dp, is approximately six times the initial Fe film thickness, tFe: Dp ≈ 6tFe. After deposition of relatively thick silicon layers on CNTs made with different Fe thicknesses, followed by oxidation, all of the resulting CNT-templated SiO2 wires had nearly the same diameter. Consequently, their surface areas were very similar, although their areal densities on the TLC plates were not because thinner catalyst layers produce denser CNT forests. For tFe = 6 nm, nanotube growth appears to be base growth, not tip growth. Best TLC separations of a test dye mixture were obtained with plates prepared with 6 or 4 nm of catalyst. Calculations suggest a loss of surface area for TLC plates made with thicker Fe layers as a result of fewer, thicker CNTs, where the density of silica nanotubes (device surface area) goes approximately as 1/tFe2. While the focus of this paper is toward a greater understanding of the processing conditions that lead to the best TLC plates, a baseline separation of three analgesics (caffeine, phenacetine, and propyphenazone) is shown on a normal phase TLC plate grown with 6 nm of iron.
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81.07.Bc Nanocrystalline materials
81.07.De Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Bg Chromatography
68.37.Ps Atomic force microscopy (AFM)

Wet chemical etching process for wafer scale isolation and interconnection of GaSb based device layers grown on GaAs substrates

Jung Min Kim, Partha S. Dutta, Eric Brown, Jose M. Borrego, and Paul Greiff

J. Vac. Sci. Technol. B 31, 031204 (2013); http://dx.doi.org/10.1116/1.4801008 (6 pages)

Online Publication Date: 15 April 2013

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An optimized selective wet chemical etching process using potassium sodium tartrate solutions and citric acid solutions has been reported for wafer scale isolation and interconnection of GaSb based device structures grown on GaAs substrates. Uniformly etched surfaces with vertical side walls with minimal under-cutting and edge rounding, and smooth surface morphology have been achieved over a 2 in. (50 mm) diameter wafer using an optimized etching conditions, etchant preparation process, and specific ratios of the etchant ingredients. Repeatable etch rates for GaSb of approximately 330 nm/min and 12 nm/s for GaAs have been obtained. Using the developed process, wafer scale monolithically interconnected GaSb devices as well as modules on semi-insulating GaAs substrates can be fabricated for a variety of optoelectronic applications.
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81.65.Cf Surface cleaning, etching, patterning
85.30.De Semiconductor-device characterization, design, and modeling
68.35.bg Semiconductors
02.60.Pn Numerical optimization

Epitaxial NiInGaAs formed by solid state reaction on In0.53Ga0.47As: Structural and chemical study

Pini Shekhter, Shlomo Mehari, Dan Ritter, and Moshe Eizenberg

J. Vac. Sci. Technol. B 31, 031205 (2013); http://dx.doi.org/10.1116/1.4802917 (5 pages)

Online Publication Date: 25 April 2013

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Thin epitaxial layers of NiInGaAs formed by solid state reaction of Ni on (100) In0.53Ga0.47As are used as metal source and drain regions for In0.53Ga0.47As metal oxide field effect transistors. Here, the authors present a structural and chemical analysis of this phase. The stoichiometry of the layer was determined as Ni2In0.53Ga0.47As. Transmission electron microscopy revealed an abrupt interface and a detailed x-ray diffraction analysis showed that the layer is of a hexagonal lattice, which grows epitaxially with the orientation relations of {100}InGaAs||{100}NiInGaAs; 〈01math〉InGaAs||[001]NiInGaAs. Only one domain can be observed in this epitaxial growth. Understanding the structure of these layers is a crucial step not only in their incorporation into InGaAs based devices but also a step toward novel devices.
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68.55.ag Semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Np Solid phase epitaxy; growth from solid phases
85.30.Tv Field effect devices

Using the 3D beam propagation method to model the effects of lithographic roughness on the attenuation of highly multimodal polymer waveguides

Nicholas Riegel, Christopher Middlebrook, Kevin Kruse, and Michael Roggemann

J. Vac. Sci. Technol. B 31, 031206 (2013); http://dx.doi.org/10.1116/1.4802979 (6 pages)

Online Publication Date: 1 May 2013

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Waveguide sidewall surface roughness is a primary cause of attenuation in lithographically defined, multimode, polymer optical waveguides. Techniques that are currently employed to analyze the effect of roughness on highly multimode waveguides such as coupled mode theory are not easily adaptable to more complicated structures. For example, this technique cannot be used for waveguides that utilize bends, where the modal distribution can not be easily calculated. In this paper, the beam propagation method is used to find sidewall roughness losses empirically. Straight waveguides of different roughnesses are first modeled, and the modeled results are compared to the attenuation of manufactured straight waveguides. The roughness that closely matches the manufactured waveguides attenuation is then verified further by matching the attenuation of waveguides containing 90° bends.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
42.70.Jk Polymers and organics

Growth properties and resistive switching effects of diamond-like carbon films deposited using a linear ion source

Wei Dai, Peiling Ke, and Aiying Wang

J. Vac. Sci. Technol. B 31, 031207 (2013); http://dx.doi.org/10.1116/1.4803741 (6 pages)

Online Publication Date: 6 May 2013

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Diamond-like carbon (DLC) films were prepared using an anode-layer linear ion beam source with C2H2 as the precursor and various negative bias voltages. The growth properties, microstructures, mechanical properties, and the resistive switching behaviors of the as-deposited DLC films were investigated as a function of bias voltage. The results showed that adjusting the bias voltage could vary the carbon atomic bonding structure (sp3/sp2 carbon hybridized bonding) of the films. The sp3/sp2 ratio initially increased as bias voltage increased and then decreased once the bias voltage exceeded −100 V. The variations in the film hardness and residual stress at different bias voltages were similar in profile to the sp3 bond fractions, indicating that both the residual stress and the mechanical properties of the DLC films were highly dependent on sp3-C bonding structures. The resistive switching characteristics of the DLC films were studied via a Cu/DLC/Pt cell structure. It was found that the bias voltages had a significant influence on the resistive switching behaviors of the DLC films. The film deposited with a bias voltage of 0 V showed excellent resistive switching effects with an ON/OFF ratio higher than 70 and device yield of about 90%, while the films deposited with higher bias voltages presented poor resistive switching effects. The sp2/sp3 ratio of the films was believed to account for the favorable resistive switching performances.
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81.05.ug Diamond
68.55.A- Nucleation and growth
81.15.Jj Ion and electron beam-assisted deposition; ion plating
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.60.Bs Mechanical and acoustical properties

Analyzing pattern retention for multilayer focused ion beam induced quantum dot structures

Marta Luengo-Kovac, Timothy W. Saucer, Andrew J. Martin, Joanna Millunchick, and Vanessa Sih

J. Vac. Sci. Technol. B 31, 031208 (2013); http://dx.doi.org/10.1116/1.4804278 (4 pages)

Online Publication Date: 9 May 2013

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Atomic force microscopy was used to investigate the effects of templating parameters on focused ion beam patterned single-, two-, and three-layer InAs/GaAs(001) quantum dot structures. The number of layers, focused ion beam dwell time, and pattern spacing affected the fidelity of the quantum dots. The highest single dot fidelities were found in regions with 1 and 3 ms dwell times and 1 and 2 μm pattern spacings. A two-layer region patterned with 1 ms dwell time and 1 μm spacing was found to have 100% single quantum dot fidelity with no off-site dot nucleation in a 20 × 20 μm2 scan. Holes that were milled with 6 and 9 ms dwell times and 0.25 μm spacing became faceted, that is, deep, tightly packed, and rhombic, by the third layer. Autocorrelation of the images was used to analyze the periodicity and size of the features.
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81.05.Ea III-V semiconductors
68.65.Ac Multilayers
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots

Poly-(3)hexylthiophene nanowire networks for versatile fabrication of bulk heterojunctions with increased active volume

Theodore J. Kramer, Annabel R. Chew, Theanne Schiros, Ioannis Kymissis, and Irving P. Herman

J. Vac. Sci. Technol. B 31, 031209 (2013); http://dx.doi.org/10.1116/1.4802928 (8 pages)

Online Publication Date: 13 May 2013

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Spontaneous demixing of poly-(3)hexylthiophene (P3HT) and polystyrene (PS) generates a dense array of crystalline P3HT nanowires embedded in a PS matrix. The PS phase is subsequently removed, to form a network of P3HT nanowires with a greatly enhanced surface area-to-volume ratio relative to a planar P3HT film. Photovoltaic devices fabricated from these networks backfilled with either organic ([6,6]-phenyl-C61-butyric acid methyl ester (PCBM)) or inorganic (cadmium selenide (CdSe) nanocrystals) material have dramatically increased short-circuit current and power conversion efficiencies relative to planar-bilayer-prepared devices, with increases of ∼8× and ∼3× for PCBM and CdSe nanocrystals, respectively, suggesting that these devices have increased P3HT active volume. This two-step backfill technique can produce nanostructured all-organic and hybrid organic/inorganic bulk heterojunction structures that cannot be formed with traditional one-step casting methods.
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61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.05.Fb Organic semiconductors
81.07.Gf Nanowires
81.16.-c Methods of micro- and nanofabrication and processing
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Improvement of polycrystalline silicon wafer solar cell efficiency by forming nanoscale pyramids on wafer surface using a self-mask etching technique

Hsin-Han Lin, Wen-Hwa Chen, and Franklin C.-N. Hong

J. Vac. Sci. Technol. B 31, 031401 (2013); http://dx.doi.org/10.1116/1.4795862 (7 pages)

Online Publication Date: 19 March 2013

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The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl2), sulfur hexafluoride (SF6), and oxygen (O2) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120–130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6–10 min to create surface nanostructures by varying the compositions of SF6, Cl2, and O2 gas mixtures in the etching process. The wafers were then treated with acid (KOH:H2O = 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 × 156 mm2) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching.
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88.40.H- Solar cells (photovoltaics)
81.65.Cf Surface cleaning, etching, patterning
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Fabrication of large dimension aluminum air-bridges for superconducting quantum circuits

Mohammad Abuwasib, Philip Krantz, and Per Delsing

J. Vac. Sci. Technol. B 31, 031601 (2013); http://dx.doi.org/10.1116/1.4798399 (6 pages)

Online Publication Date: 4 April 2013

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Proper grounding between different ground planes in coplanar superconducting qubit circuits is important to avoid spurious resonances which increase decoherence. Here, the authors present a possible solution to suppress such undesired modes using superconducting aluminum air-bridges which have been fabricated on top of aluminum coplanar waveguide transmission lines. 3D electromagnetic simulations were done to guide the design of the air-bridges such that the input reflection (S11) of the bridges was kept at a minimum level. A fabrication method based on optical lithography techniques was developed and it resulted in air-bridges with a height of approximately 10 μm and lengths of up to 500 μm. The method can be generalized to arbitrary length air-bridge with heights even exceeding 15 μm.
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84.40.Az Waveguides, transmission lines, striplines

Bubble-free replication of large area microstructures using gas-assisted UV embossing with modified reversal imprinting and gap-retained vacuuming

Po-Hsun Huang, Han-Ming Chen, Tzu-Chien Huang, Sen-Yeu Yang, and Yi-Ting Sun

J. Vac. Sci. Technol. B 31, 031602 (2013); http://dx.doi.org/10.1116/1.4799087 (5 pages)

Online Publication Date: 5 April 2013

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Air bubble defects have been regarded as a critical problem in ultraviolet (UV)-based imprinting/embossing processes, especially in large area fabrication. This paper reports a gas-assisted UV embossing process for bubble-free replication of large area microstructures. This gas-assisted pressurizing process provides uniform embossing pressure over the whole large area, while UV curing enables the process to be performed at room temperature and low pressure. To overcome the problem of air bubble entrapments in the large area UV embossing process, the mechanisms of modified reversal imprinting and gap-retained vacuuming have been developed and used. Experimental results show that the microstructures have been successfully transferred from the stamper to the polymethylmethacrylate substrate with the size of 230 × 203 mm2 inducing no air bubble defects.
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61.72.-y Defects and impurities in crystals; microstructure
78.40.Ha Other nonmetallic inorganics
82.35.-x Polymers: properties; reactions; polymerization
81.16.-c Methods of micro- and nanofabrication and processing

Modified knife-edge method for current density distribution measurements in e-beam writers

Jan Bok, Vladimír Kolařík, Miroslav Horáček, Milan Matějka, and František Matějka

J. Vac. Sci. Technol. B 31, 031603 (2013); http://dx.doi.org/10.1116/1.4802920 (6 pages)

Online Publication Date: 1 May 2013

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In this paper, the authors present a modified knife-edge method for two-dimensional current density mapping in electron-beam writing systems. This method is applicable in rectangular and in variable-shaped e-beam writers with a fixed mutual position of the e-beam and the 1st shutter during exposure. In contrast to other methods, the modified knife-edge method uses only native parts of the e-beam writer, giving it the advantage of easy implementation. The measurement error of our method is analyzed and the trade-off between the result accuracy, the current density resolution and the measurement duration is discussed. The presented method is demonstrated by adjusting an electron emitter in order to select a homogeneous e-beam pattern.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fabrication of metal roller mold with submicrometer feature size using contact printing photolithography technique

Kuo-Feng Huang and Yung-Chun Lee

J. Vac. Sci. Technol. B 31, 031604 (2013); http://dx.doi.org/10.1116/1.4804275 (6 pages)

Online Publication Date: 10 May 2013

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This paper presents an innovative approach for directly forming surface microstructures at submicrometer scale on the cylindrical surface of a metal roller. This roller can then serve as a roller mold in roller imprinting processes for large-area micro/nanofabrication. In the proposed approach, a novel contact printing method is used to transfer a patterned metal film from a planar soft mold to a thin photoresist (PR) layer coated on the roller surface. The pattern definition capability can easily reach submicrometer scale over a large patterning area. Subsequent ultraviolet light exposure and PR developing processes then form a layer of patterned PR microstructures on the cylindrical surface. Finally, patterned microfeatures are directly formed on the roller's surface by an additive (metal deposition) approach. The overall system design, experimental procedures, and experimental results are systematically discussed.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
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Fabrication of large-area, high-density Ni nanopillar arrays on GaAs substrates using diblock copolymer lithography and electrodeposition

Chun-Chieh Chang, Dan Botez, Lei Wan, Paul F. Nealey, Steven Ruder, and Thomas F. Kuech

J. Vac. Sci. Technol. B 31, 031801 (2013); http://dx.doi.org/10.1116/1.4798464 (5 pages)

Online Publication Date: 4 April 2013

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Large-area, ultradense Ni nanopillar arrays were fabricated directly on bare n-GaAs substrates using diblock copolymer lithography and electrodeposition. The Ni nanopillar arrays are hexagonally arranged, exhibiting an average pillar diameter of ∼24 nm, and an areal density of ∼1011/cm2 over an entire surface area of 1 cm × 1 cm. These arrays represent large-scale, highly dense, sub-30 nm metal-nanopillar arrays made on III-V semiconductor substrates suitable as pattern masks. The fabrication method offers a simple and effective route to manufacturing large-area, highly dense, sub-30 nm metal nanostructures for III-V optoelectronic devices, in order to enhance their performance and functionalities.
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61.46.-w Structure of nanoscale materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.Bc Nanocrystalline materials
81.15.Pq Electrodeposition, electroplating
81.16.Nd Micro- and nanolithography
82.45.Qr Electrodeposition and electrodissolution
83.80.Uv Block copolymers

Tungsten-based pillar deposition by helium ion microscope and beam-induced substrate damage

Kazuyuki Kohama, Tomohiko Iijima, Misa Hayashida, and Shinichi Ogawa

J. Vac. Sci. Technol. B 31, 031802 (2013); http://dx.doi.org/10.1116/1.4800983 (8 pages)

Online Publication Date: 10 April 2013

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The authors use a helium ion microscope (HIM) equipped with a tungsten hexacarbonyl gas injection system (GIS) to form tungsten-based pillars on carbon and silicon substrates by helium ion beam-induced deposition. Tungsten-based pillars with a width of ∼40 nm and height of ∼2 μm (aspect ratio of ∼50) are successfully fabricated using the HIM-GIS method. The pillars consist of face-centered cubic WC1−x and/or W2(C, O) grains. Columnar voids with a width of 1–15 nm form in the center of the pillars, suggesting that the pillars are continuously sputter-etched by the incident helium ion beam during deposition. In addition, the authors observe beam irradiation damage in the form of blistering of the Si substrate at the interface between the pillar and Si substrate. The columnar void width and Si blister height decreases as the volumetric growth rate of the pillars increases regardless of the deposition parameters. The authors consider that at least three phenomena compete during pillar formation, namely pillar deposition, sputter-etching, and Si blistering. Although there are numerous parameters involved in HIM-GIS deposition, it appears that the volumetric growth rate determines both the microstructure of the tungsten-based pillars and the degree of substrate damage.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.80.Jh Ion radiation effects

Ozone priming of patterned carbon nanotube forests for subsequent atomic layer deposition-like deposition of SiO2 for the preparation of microfabricated thin layer chromatography plates

David S. Jensen, Supriya S. Kanyal, Nitesh Madaan, Andrew J. Miles, Robert C. Davis, Richard Vanfleet, Michael A. Vail, Andrew E. Dadson, and Matthew R. Linford

J. Vac. Sci. Technol. B 31, 031803 (2013); http://dx.doi.org/10.1116/1.4801834 (8 pages)

Online Publication Date: 1 May 2013

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The authors report the ozonation of patterned, vertically aligned carbon nanotube (CNT) forests as a method of priming them for subsequent pseudo atomic layer deposition (ψ-ALD) (alternating layer deposition) of silica to produce microfabricated, CNT-templated thin layer chromatography (TLC) plates. Gas phase ozonation simplifies our deposition scheme by replacing two steps in our previous fabrication process: chemical vapor deposition of carbon and ALD of Al2O3, with this much more straightforward priming step. As shown by x-ray photoelectron spectroscopy (XPS), ozonation appears to prime/increase the number of nucleation sites on the CNTs by oxidizing them, thereby facilitating conformal growth of silica by ψ-ALD, where some form of priming appears to be necessary for this growth. (As shown previously, ψ-ALD of SiO2 onto unprimed CNTs is ineffective and leads to poor quality depositions.) In conjunction with a discussion of the challenges of good peak fitting of complex C 1s XPS narrow scans, the authors present an analysis of their C 1s data that suggests an increase in oxidized carbon, particularly the C=O group, with increasing oxygen content of the CNT forests. After coating with SiO2, the CNTs are removed by elevated temperature air oxidation, the SiO2 is rehydrated, and the plates are coated with 3-aminopropyltriethoxysilane (APTES). The resulting APTES-coated plates separate various fluorescent dyes giving results that are generally at least as good as those the authors reported previously with their more complicated fabrication/priming scheme. TLC plates with different geometries are microfabricated, where plates with narrower channels show longer run times (lower mobile phase velocities) and plates with narrower features appear to give higher efficiencies.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.07.De Nanotubes
82.80.Bg Chromatography
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
64.60.Q- Nucleation

Distance dependence of tunneling thermovoltage on metal surfaces

Petro Maksymovych

J. Vac. Sci. Technol. B 31, 031804 (2013); http://dx.doi.org/10.1116/1.4803156 (6 pages)

Online Publication Date: 9 May 2013

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Thermovoltage in a tunnel junction of a scanning tunneling microscope is a valuable observable that is known to have chemical sensitivity. Tunneling thermovoltage is typically measured at a fixed tip–surface distance. Here the author presents distance-dependent thermovoltage measurements that were systematically acquired over Ag(111) surface with a small coverage of adsorbates. The author confirms that the distance dependence can be used to obtain thermovoltage contrast due to the difference in the tunneling barrier height, and reveals that adjusting the width of the tunneling gap can significantly enhance thermoelectronic contrast. Furthermore, comparing tunneling thermovoltage and a synchronously acquired tunneling current as a function of gap width provided a direct verification of the Stovneng–Lipavsky model, which is often used to interpret tunneling thermovoltage experiments. Finally, the author shows that the distance-dependent thermovoltage can potentially be used to evaluate a thermal gradient in an atomic-scale tip–surface junction without explicit temperature calibration, which has so far not been achievable experimentally.
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07.20.-n Thermal instruments and apparatus
07.79.Cz Scanning tunneling microscopes

High-resolution transmission electron microscope observations of multiwalled carbon nanotube microstructures grown by plasma enhanced chemical vapor deposition

Mireille Gaillard, Christian Kübel, Chantal Boulmer-Leborgne, Di Wang, Nadjib Semmar, Agnès Petit, and Eric Millon

J. Vac. Sci. Technol. B 31, 031805 (2013); http://dx.doi.org/10.1116/1.4804543 (8 pages)

Online Publication Date: 15 May 2013

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Vertically aligned carbon nanotubes (CNTs) are grown by plasma enhanced chemical vapor deposition and are analyzed by high-resolution transmission electron microscopy. With this process, the growth of vertically aligned and densely packed CNTs can only be obtained with an Fe catalyst on an Si3N4 support or with an Ni catalyst on a TiN support. The authors observe that base- and tip-growth modes occur simultaneously for the Fe/Si3N4 system, whereas in the Ni/TiN system only the base-growth mode is observed. When using the multilayer catalyst FeNi (2:1), growth occurs on both supports. These structures are quite similar to those obtained with a pure Fe or Ni catalyst on their corresponding support. Growth at lower temperatures, down to 550 °C, shows that at temperatures high enough to just activate the catalyst, the structures obtained are not significantly influenced by the growth temperature, but rather by the catalyst-support system and other growth conditions.
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81.07.De Nanotubes
68.65.Ac Multilayers
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
52.77.Dq Plasma-based ion implantation and deposition
68.37.Lp Transmission electron microscopy (TEM)
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Selective area growth of InAs on InP with dielectric mask

C. Y. Chou, A. Torfi, and W. I. Wang

J. Vac. Sci. Technol. B 31, 031806 (2013); http://dx.doi.org/10.1116/1.4804400 (4 pages)

Online Publication Date: 16 May 2013

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Low resistance ohmic contacts are important for high frequency applications of InP-based heterojunction bipolar transistors and high electron mobility transistors. In this paper, the authors investigate the use of an InAs layer as the low-resistance ohmic contact to these heterostructure devices. Selective area crystal growth of InAs on a dielectric [benzocyclobutene (BCB) polymer] covered InP(100) was carried out by molecular beam epitaxy (MBE). Additionally, direct growth of InAs on InP substrates was performed to allow comparisons with InAs grown on BCB-covered InP. Different growth temperatures were tested to optimize the crystal quality of the InAs layer, which was characterized by scanning electron microscope and x-ray diffraction. Heavy doping of InAs using Te was carried out to determine the lowest sheet resistance. As the substrate temperature was increased from 210 to 350 °C, the crystallinity improved from a polycrystal layer to a single crystal layer with corresponding improvement of surface morphology. Moreover, sharp x-ray diffraction indicated the 3.3% lattice-mismatch was fully relaxed without misorientation. However, a trade off was reached around 290 °C between crystallinity and optimized dopant incorporation of Te into InAs for lowest sheet resistance. The results indicate the potential of Te-doped InAs as emitter contact for high frequency devices by MBE.
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81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.uj III-V and II-VI semiconductors
68.47.Fg Semiconductor surfaces
73.40.Ns Metal-nonmetal contacts
85.30.Tv Field effect devices
85.30.Pq Bipolar transistors
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Fabrication of 3D charged particle trap using through-silicon vias etched by deep reactive ion etching

Ankita Verma, Joshah Jennings, Ryan D. Johnson, Marc H. Weber, and Kelvin G. Lynn

J. Vac. Sci. Technol. B 31, 032001 (2013); http://dx.doi.org/10.1116/1.4799662 (9 pages)

Online Publication Date: 4 April 2013

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Positrons are charged antiparticles that annihilate upon contact with electrons or any form of matter. Two of the authors (Lynn and Weber) have proposed a new approach to store large numbers of charged particles such as positrons. The proposed structure consists of thousands of 0.1-mm-diameter holes etched through silicon wafers, which are then stacked axially to form cylindrical microtubes to store a large number of positrons. The authors used deep reactive ion etching on the wafers to create the through-holes with smooth and straight sidewalls. To produce the best possible etching results, they iteratively modified the etching parameters, including the chamber pressure, temperature, radio frequency power, inductively coupled plasma power, SF6/O2 gas flow, and O2 gas content. These iterations addressed the fabrication issues that were encountered, such as bowing, notching, undercutting, nonuniform etch rates across the wafer, and preferential etching along certain crystal planes. The trench widths were calibrated to match the etch rates between all the wafer features. The final results enabled the etching of through-wafer vias with straight sidewalls (89.9–90.1°), smooth surfaces, and high aspect ratios (≥5:1) with minimal defects. This paper describes the etching process used to produce these vias.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.65.Cf Surface cleaning, etching, patterning

Demonstration of electrical connectivity between self-assembled structures

Madhav Rao, John C. Lusth, and Susan L. Burkett

J. Vac. Sci. Technol. B 31, 032002 (2013); http://dx.doi.org/10.1116/1.4802914 (11 pages)

Online Publication Date: 1 May 2013

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A novel way of three dimensional (3D) chip stacking has been designed in a view to improve heat dissipation across the layers. Solder-based self assembled (SBSA) structures have been designed as 3D posts on simulated through silicon vias to demonstrate the concept. The fabrication of SBSA structures using a low temperature solder alloy and dip soldering method is described. Previously, two types of soldering—face soldering and edge soldering—were studied to fabricate SBSA structures. Face soldering refers to deposition of solder on the complete metal face whereas edge soldering refers to selective deposition of solder on only the edges of the metal face. Mechanical grinding of the 3D structures shows that face soldered SBSA structures were void free and robust enough to be used as a connection post for chip stacking. Edge soldered SBSA structures collapsed when grinding was performed. This suggests the edge soldered 3D structure may only be partially filled. Face soldered SBSA structures provide a solder bump that serves as a connection path in the integration of dissimilar electronic technologies. Cylindrical copper posts, developed in a previous project, can be an effective approach to integrated circuit stacking. However, the SBSA post provides more variety in size and shape and can serve as a reservoir for solder to aid in chip bonding. The solder bumps are heat resistant, and uniform thicknesses were obtained across a large array of SBSA structures. The electrical durability of SBSA posts were determined by completing I-V measurements after thermal treatment. SBSA posts were subjected to thermal cycling with temperatures ranging from room temperature to 300 °C. The interconnected SBSA posts are shown to be stable until 165 °C with little variation in measured resistance.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.40.Ls Metallization, contacts, interconnects; device isolation
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Influence of barrier form on Fowler–Nordheim plot analysis

Andreas Fischer, Marwan S. Mousa, and Richard G. Forbes

J. Vac. Sci. Technol. B 31, 032201 (2013); http://dx.doi.org/10.1116/1.4795822 (9 pages)

Online Publication Date: 22 March 2013

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Recent research has described an improved method of Fowler–Nordheim (FN) plot analysis, based on the definition and evaluation of a slope correction factor and a new form of intercept correction factor. In this improved approach, there exists a basic approximation that neglects certain terms in the general theory, and focuses on the influence of the form of the tunneling barrier on the values of basic slope (σB) and intercept (ρB) correction factors. Simple formulae exist that allow these to be evaluated numerically for a barrier of arbitrary well-behaved form. This paper makes an initial exploration of the effects of barrier form on FN plot analysis. For a planar emitter, two models for the correlation-and-exchange (C&E) potential energy (PE) are used. For the Schottky–Nordheim barrier, it is shown that numerical and analytical approaches generate equivalent results. This agreement supports the validity of the numerical methods used. Comparisons with results for the Cutler–Gibbons barrier show that small differences in the assumed C&E PE make little difference to values of σB and ρB. Schottky's planar image PE has then been used, in conjunction with the electrostatic PE variation associated with a spherical emitter model, to explore the influence of apex radius ra on correction-factor values, for values of ra ≥ 20 nm. Both σB and ρB increase significantly as ra decreases, especially ρB. At low values of barrier field F, σB depends approximately linearly on 1/F, with a slope that depends on ra. Suggestions are made for how the exploratory work described in this paper might be extended.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Gk Tunneling

Study of hydrogen detection response time with Pt-gated diodes fabricated on AlGaN/GaN heterostructure

Yuyin Xi, Lu Liu, Ya-Hsi Hwang, Oluwadamilola Phillips, Fan Ren, Stephen J. Pearton, Jihyun Kim, Chien-Hsing Hsu, Chien-Fong Lo, and Jerry Wayne Johnson

J. Vac. Sci. Technol. B 31, 032202 (2013); http://dx.doi.org/10.1116/1.4798612 (5 pages)

Online Publication Date: 3 April 2013

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The hydrogen detection response time of Pt-gated diode sensors fabricated on AlGaN/GaN heterostructure as a function of the hydrogen concentration was investigated. A new method to extract the response time, taking the derivative of diode current, was proposed and shown to reduce the response time of detecting 1% hydrogen by about 60% as compared to the response time defined as the diode current reaching 90% of its total changes, t90. Hydrogen-sensing experiments were conducted at different temperatures, and an Arrhenius plot of the data determined an activation energy of 17.7 kJ/mole for the sensing process.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Kk Junction diodes

Methane detection using Pt-gated AlGaN/GaN high electron mobility transistor based Schottky diodes

Yuyin Xi, Lu Liu, Fan Ren, Stephen J. Pearton, Jihyun Kim, Amir Dabiran, and Peter P. Chow

J. Vac. Sci. Technol. B 31, 032203 (2013); http://dx.doi.org/10.1116/1.4803743 (5 pages)

Online Publication Date: 9 May 2013

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Pt-gated AlGaN/GaN high electron mobility transistor based Schottky diodes were employed to detect methane. A detection sensitivity >100 was obtained for the diodes under reverse bias, and this was one order of magnitude higher than the sensitivity of the diodes operated under forward bias. A new method to extract the response time was demonstrated by taking the derivative of diode current, allowing a reduction in the sensor response time by 80%. Methane sensing experiments were conducted at different temperatures, and an Arrhenius plot of the data determined an activation energy of 57 kJ/mol for the sensing process.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes

Nickel nanoparticle size and density effects on non-volatile memory performance

Emanuele Verrelli, Giorgos Galanopoulos, Ilias Zouboulis, and Dimitris Tsoukalas

J. Vac. Sci. Technol. B 31, 032204 (2013); http://dx.doi.org/10.1116/1.4804407 (7 pages)

Online Publication Date: 13 May 2013

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In this work, the authors present non-volatile memory devices based on nickel nanoparticles deposited by a novel sputtering process at room temperature and demonstrate and discuss the effect of nanoparticle size and density upon optimum device performance. The devices use a mixed dielectric stack comprised of a silicon dioxide tunneling layer and a hafnium oxide layer formed at low temperature. This allows for fabrication of devices with a relatively small thermal budget and superior performance in terms of memory windows and operating voltages. At voltages as low as 8 V, the memory window of the devices is as large as 5 V. Charge retention measurements confirm the non-volatility of these devices for up to 10 years, and analysis of the leakage currents sheds light on the mechanisms involved that create these charge retention characteristics.
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84.30.Sk Pulse and digital circuits

Enhanced light output from light emitting diodes with two-dimensional cone-shape nanostructured surface

Benzhong Wang and Soo-Jin Chua

J. Vac. Sci. Technol. B 31, 032205 (2013); http://dx.doi.org/10.1116/1.4804406 (5 pages)

Online Publication Date: 15 May 2013

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A simple, inexpensive and high throughput approach for creating two-dimensional cone-shaped nanostructures is reported. A self-assembled array of polystyrene nanospheres is employed as the primary mask to fabricate such structures on AlGaInP red light emitting diodes, resulting in over two times increase of light output power. An orderly array of cones show higher intensity emitted in the forward direction than one that is randomly arranged.
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85.60.Jb Light-emitting devices

Effect of chemical bonding states in TaOx base layers on rectifying bipolar resistive switching characteristics

Jonggi Kim, In-Su Mok, Youngjae Kim, Kyumin Lee, Dae-Hong Ko, and Hyunchul Sohn

J. Vac. Sci. Technol. B 31, 032206 (2013); http://dx.doi.org/10.1116/1.4806766 (5 pages)

Online Publication Date: 15 May 2013

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In this study, the authors investigated the rectifying bipolar resistive switching characteristics of Pt/HfO2/TaOx/Pt heterostacks with respect to the chemical bonding states of the TaOx base layer and the physical properties of the insulator layer. The authors demonstrated that the migration of oxygen ions at the interface between the HfO2 insulator layer and the TaOx base layer produced the rectifying bipolar resistive switching, and the switching current could be controlled via the oxygen concentration in the TaOx layer. They also observed that the current at the high-resistance state decreased with increasing thickness of the HfO2 insulator layer. Rectifying bipolar resistive switching behavior was additionally demonstrated by using an Al2O3 layer as an insulator instead of HfO2.
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84.30.Sk Pulse and digital circuits
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Structural, magnetic, and nanoscale switching properties of BiFeO3 thin films grown by pulsed electron deposition

Hongxue Liu, Ryan Comes, Yonghang Pei, Jiwei Lu, and Stuart A. Wolf

J. Vac. Sci. Technol. B 31, 032801 (2013); http://dx.doi.org/10.1116/1.4802924 (4 pages)

Online Publication Date: 23 April 2013

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The authors report the epitaxial growth of BiFeO3 by pulsed electron deposition and the resulting crystal quality, magnetic and nanoscale switching properties. X-ray diffraction shows high quality single phase, epitaxial (001) oriented films grown on SrTiO3 (001) substrates. Both field and temperature dependent magnetic properties reveal an antiferromagnetic behavior of the films. For the film with a SrRuO3 bottom electrode, an exchange-enhancement effect between antiferromagnetic BiFeO3 and ferromagnetic SrRuO3 was observed at low temperature. The piezoelectric force microscopy and switching spectroscopy measurements demonstrate the local domain switching process and suggest that the BiFeO3 films are high quality ferroelectrics.
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75.75.Cd Fabrication of magnetic nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Dj E-beam and hot filament evaporation deposition
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Molecular beam epitaxial growth of ultralow absorption GaN high electron mobility transistor material on sapphire substrates for infrared transparent conductors

William E. Hoke, Amanda J. Kirchner, John J. Mosca, Daniel P. Resler, Theodore D. Kennedy, Michael Holz, Amanda J. Kerr, and Steven R. Collins

J. Vac. Sci. Technol. B 31, 03C101 (2013); http://dx.doi.org/10.1116/1.4769895 (5 pages)

Online Publication Date: 7 December 2012

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GaN HEMT structures have been grown on sapphire substrates that exhibit very low absorption loss at 1 μm and low sheet resistance, which are attractive properties for infrared transparent conductors. Initial GaN HEMT/sapphire films showed highly variable absorptions, which were determined to be caused by oxygen outdiffusion from the sapphire substrate into the AlN buffer layer. Growth conditions were modified enabling reproducible growth of low absorption and low sheet resistance material. Absorption losses as low as 0.1% with concomitant film conductivities of 350 Ω/sq or less were demonstrated. Consequently, free carriers in the GaN HEMT channel do not cause significant infrared absorption. The concomitant properties of low absorption and low sheet resistance exceed the properties of transparent conducting oxides. These properties of the GaN HEMT/sapphire structure are also more thermally stable compared to transparent conducting oxides. The low absorption characteristic of the GaN HEMT/sapphire structure is expected to extend into the visible spectrum enabling visible transparent conductor applications as well.
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85.30.Tv Field effect devices
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Molecular beam epitaxy of highly mismatched N-rich GaN1−xSbx and InN1−xAsx alloys

Sergei V. Novikov, Kin M. Yu, Alejandro Levander, Douglas Detert, Wendy L. Sarney, Zuzanna Liliental-Weber, Martin Shaw, Robert W. Martin, Stefan P. Svensson, Wladek Walukiewicz, and C. Thomas Foxon

J. Vac. Sci. Technol. B 31, 03C102 (2013); http://dx.doi.org/10.1116/1.4774028 (5 pages)

Online Publication Date: 8 January 2013

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GaN materials alloyed with group V anions form the so-called highly mismatched alloys (HMAs). Recently, the authors succeeded in growing N-rich GaN1−xAsx and GaN1−xBix alloys over a large composition range by plasma-assisted molecular beam epitaxy (PA-MBE). Here, they present first results on PA-MBE growth and properties of N-rich GaN1−xSbx and InN1−xAsx alloys and compare these with GaN1−xAsx and GaN1−xBix alloys. The enhanced incorporation of As and Sb was achieved by growing the layers at extremely low growth temperatures. Although layers become amorphous for high As, Sb, and Bi content, optical absorption measurements show a progressive shift of the optical absorption edge to lower energy. The large band gap range and controllable conduction and valence band positions of these HMAs make them promising materials for efficient solar energy conversion devices.
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88.40.J- Types of solar cells
71.20.Gj Other metals and alloys
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Metastable CdSe/MgSe quantum wells prepared by MBE with near IR intersubband absorption

Aidong Shen, Guopeng Chen, Kuaile Zhao, Jung-Tso Lai, and Maria C. Tamargo

J. Vac. Sci. Technol. B 31, 03C103 (2013); http://dx.doi.org/10.1116/1.4789478 (3 pages)

Online Publication Date: 30 January 2013

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The authors report, for the first time, the growth of a metastable CdSe/MgSe quantum well structure by molecular beam epitaxy. The structure was grown on InP substrate with thin ZnCdSe and InGaAs buffers. To maintain the zincblende structure of MgSe (which naturally favors rocksalt structure), a ZnCdSe spacer layer was inserted between CdSe/MgSe quantum wells. The structural and optical properties of the sample were characterized by high-resolution x-ray diffraction and photoluminescence measurements. Intersubband transitions in the near infrared region were observed.
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81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
78.67.De Quantum wells
81.05.Dz II-VI semiconductors

Structural and electrical characterization of InN, InGaN, and p-InGaN grown by metal-modulated epitaxy

Michael Moseley, Brendan Gunning, Jonathan Lowder, W. Alan Doolittle, and Gon Namkoong

J. Vac. Sci. Technol. B 31, 03C104 (2013); http://dx.doi.org/10.1116/1.4790865 (6 pages)

Online Publication Date: 8 February 2013

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InN, high indium content InGaN, and Mg-doped InGaN were grown by metal modulated epitaxy (MME). Transient reflection high-energy electron diffraction intensities were analyzed during the growth of InN and found to be similar to that previously reported for GaN and AlN. The x-ray diffraction rocking curve and background electron concentration of InN grown by MME were found to be respectable in comparison to recent reports in literature. InGaN alloys grown by MME were also investigated, and a method for detecting indium surface segregation was demonstrated. It was found that the shutter modulation scheme could be modified to prevent phase separation by indium surface segregation, and a range of single-phase InGaN samples with indium contents throughout the miscibility gap were grown. Using the discovered method of suppressing phase separation, several p-InxGa1 − xN samples were grown with indium contents from x = 0 to 0.22. A maximum hole concentration of 2.4 × 1019 cm−3 was detected by Hall effect characterization, demonstrating feasibility of these p-InGaN layers for use in several device applications.
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68.55.ag Semiconductors
68.35.Dv Composition, segregation; defects and impurities
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
64.75.Bc Solubility

MBE grown GaAsBi/GaAs double quantum well separate confinement heterostructures

Dongsheng Fan, Perry C. Grant, Shui-Qing Yu, Vitaliy G. Dorogan, Xian Hu, Zhaoquan Zeng, Chen Li, Michael E. Hawkridge, Mourad Benamara, Yuriy I. Mazur, Gregory J. Salamo, Shane R. Johnson, and Zhiming M. Wang

J. Vac. Sci. Technol. B 31, 03C105 (2013); http://dx.doi.org/10.1116/1.4792518 (5 pages)

Online Publication Date: 14 February 2013

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GaAsBi/GaAs double quantum wells and double quantum well separate confinement heterostructures are grown at low temperatures using molecular beam epitaxy. Methods of achieving identical quantum wells in double quantum well structures without growth interruption are proposed and implemented. Cross-sectional transmission electron microscopy and room temperature photoluminescence measurements indicate that the samples have excellent structural and optical properties. The high optical quality of the samples is attributed to the surfactant effect of Bi throughout the low temperature growth of GaAs and AlGaAs layers. The proposed approach can be extended to grow laser diode structures with multiple quantum well separate confinement heterostructures containing more identical quantum wells.
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68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.55.Px Semiconductor lasers; laser diodes

MBE growth of GaSb-based photodetectors on 6-inch diameter GaAs substrates via select buffers

Joel M. Fastenau, Dmitri Lubyshev, Yueming Qiu, Amy W. K. Liu, Edwin J. Koerperick, Jon T. Olesberg, and Dennis Norton, Jr.

J. Vac. Sci. Technol. B 31, 03C106 (2013); http://dx.doi.org/10.1116/1.4792516 (6 pages)

Online Publication Date: 15 February 2013

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GaSb-based, 6.1 Å lattice-constant, infrared photodetector materials were grown on large diameter, 6-in. GaAs substrates by molecular beam epitaxy. Multiple metamorphic buffer architectures, including bulk GaSb nucleation, AlAsSb superlattices, and graded GaAsSb ternary alloys, were investigated to bridge the 7.8% mismatch gap between the GaAs substrates and the GaSb-based epitaxial layers. Unique surface morphologies and crystal structure properties, as revealed by atomic force microscopy and cross-section transmission electron microscopy, pointed to different relaxation mechanisms for different buffer architectures. GaSb nucleation results in a more island-like surface morphology with a mix of 90° misfit and 60°-type threading dislocations, while the graded ternary buffer results in a cross-hatch surface morphology with effective filtering of the threading dislocations. Low root-mean-square roughness values of 5–20 Å were obtained for this type of metamorphic epilayer growth. A generic InAsSb/AlAsSb nBn photodiode structure, where the first “n” is the contact layer, the “B” is the wide-bandgap barrier layer, and the second “n” is the n-type narrow bandgap absorber layer, with ∼4 μm cutoff wavelength was grown on 6 in. GaAs substrates using the different metamorphic buffers. Cross-wafer optical and structural measurements showed excellent epitaxial layer uniformity, with PL wavelength variation <0.1 μm. Dark currents of 2–3 × 10−6 A/cm2 were measured on devices fabricated from the photodiode material grown on GaAs. This was about 5-times higher than measured on the same structure grown on GaSb substrates. This work demonstrates a promising path to satisfy the increasing demand for even larger area focal plane array detectors in a commercial production environment.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Dw Photodiodes; phototransistors; photoresistors

Three-dimensional GaN templates for molecular beam epitaxy of nonpolar InGaN/GaN coaxial light-emitting diodes

Ashwin K. Rishinaramangalam, Michael N. Fairchild, Stephen D. Hersee, Ganesh Balakrishnan, and Daniel F. Feezell

J. Vac. Sci. Technol. B 31, 03C107 (2013); http://dx.doi.org/10.1116/1.4792519 (7 pages)

Online Publication Date: 15 February 2013

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This work highlights the development of three-dimensional (3D) GaN templates grown by metal organic vapor phase epitaxy (MOVPE). These templates are ideally suited for the subsequent growth of nonpolar (1math00) m-plane InGaN-based coaxial wire/wall light-emitting diodes (LEDs) using molecular beam epitaxy (MBE). The use of MBE is expected to result in increased indium incorporation on the (1math00) m-plane, compared with growth using MOVPE, which provides an attractive approach for the development of nonpolar green LEDs. While planar free-standing m-plane GaN substrates are prohibitively expensive (approximately ∼$500 per cm2), the coaxial LED approach offers an attractive lower-cost alternative. These nonpolar nanoscale LED templates are also free from threading dislocations and are expected to provide a number of benefits, including higher light extraction and a larger effective active region area. Previous work in our group has demonstrated the controlled growth of GaN nanowires using a catalyst-free selective-area MOVPE growth method. The present work extends this method to grow 3D GaN templates in various aperture geometries, resulting in smooth m-plane GaN using a scalable and industrially viable high-quality GaN growth technique. In addition to m-plane sidewalls, the authors also demonstrate semipolar (1math01) inclined sidewalls. This orientation has been shown to incorporate indium at a higher rate during MOVPE growth, in comparison to both c-plane and m-plane.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Jb Light-emitting devices
68.55.ag Semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Causes and elimination of pyramidal defects in GaSb-based epitaxial layers

Lee M. Murray, Asli Yildirim, Sydney R. Provence, Dennis T. Norton, Thomas F. Boggess, and John P. Prineas

J. Vac. Sci. Technol. B 31, 03C108 (2013); http://dx.doi.org/10.1116/1.4792515 (6 pages) | Cited 1 time

Online Publication Date: 20 February 2013

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Here, the authors report on the occurrence, cause, and elimination of pyramidal defects in layers of GaSb grown by molecular beam epitaxy on GaSb substrates. These defects are typically 3–8 nm high, 1–3 μm in diameter, and shaped like pyramids. Their occurrence in the growth of GaSb buffer layers can propagate into subsequent layers such as GaSb, GaInAsSb, and GaSb/InAs superlattices. Defects are nucleated during the early stages of growth after the thermal desorption of native oxide from the GaSb substrate. These defects grow into pyramids due to a repulsive Ehrlich–Schwoebel potential on atomic step edges leading to an upward adatom current. The defects reduce in density with growth of GaSb. The insertion of a thin AlAsSb layer into the early stages of the GaSb buffer increases the rate of elimination of the defects, resulting in a smooth surface within 500 nm. The acceleration of defect reduction is due to the temporary interruption of step-flow growth induced by the AlAsSb layer. This leads to a reduced isolation of the pyramids from the GaSb epitaxial layer and allows the pyramidal defects to smooth out.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
64.60.qj Studies of nucleation in specific substances
68.55.ag Semiconductors
68.65.Cd Superlattices

Molecular beam epitaxial growth of high-reflectivity and broad-bandwidth ZnTe/GaSb distributed Bragg reflectors

Jin Fan, Xinyu Liu, Lu Ouyang, Richard E. Pimpinella, Margaret Dobrowolska, Jacek K. Furdyna, David J. Smith, and Yong-Hang Zhang

J. Vac. Sci. Technol. B 31, 03C109 (2013); http://dx.doi.org/10.1116/1.4793475 (4 pages)

Online Publication Date: 25 February 2013

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This paper reports the molecular beam epitaxial growth and characterization of high-reflectivity and broad-bandwidth distributed Bragg reflectors (DBRs) made of ZnTe/GaSb quarter-wavelength (λ/4) layers for optoelectronic applications in the midwave infrared spectral range (2–5 μm). A series of ZnTe/GaSb DBRs has been successfully grown on GaSb (001) substrates using molecular beam epitaxy (MBE). During the MBE growth, a temperature ramp was applied to the initial growth of GaSb layers on ZnTe to protect the ZnTe underneath from damage due to thermal evaporation. Post-growth characterization using high-resolution x-ray diffraction, atomic force microscopy, and transmission electron microscopy reveals smooth surface morphology, low defect density, and coherent interfaces. Reflectance spectroscopy results show that a DBR sample of seven λ/4 pairs has a peak reflectance as high as 99.0% centered at 2.56 μm with a bandwidth of 517 nm.
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42.79.Bh Lenses, prisms and mirrors
78.30.Fs III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.bg Semiconductors
68.55.ag Semiconductors

Growth and characterization of GaP/GaNP core/shell nanowires

Supanee Sukrittanon, YanJin Kuang (邝彦瑾), and Charles W. Tu

J. Vac. Sci. Technol. B 31, 03C110 (2013); http://dx.doi.org/10.1116/1.4793476 (4 pages)

Online Publication Date: 25 February 2013

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This paper reports on self-catalyzed vertical GaP nanowires (NWs) and GaP/GaNP core/shell NWs grown on Si(111) by gas-source molecular beam epitaxy. It was found that GaP NWs have a growth window from ∼585 °C to ∼615 °C. The low temperature limit is set by lack of adatom mobility, while the high temperature limit is set by unattainable supersaturation condition of vapor–liquid–solid growth. In the temperature window, the GaP NW diameter can be tailored by the growth temperature. A comparison of the photoluminescent spectrum between an ensemble GaP/GaNP core/shell NWs and a single NW shows that the broad and nearly identical width of the spectra probably does not originate from the variation of N composition among NWs but from the mechanism of light emission.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Uh Nanowires
81.07.Gf Nanowires
78.55.Cr III-V semiconductors

Molecular beam deposited zirconium dioxide as a high-κ dielectric for future GaN based power devices

Annett Freese, Matthias Grube, Andre Wachowiak, Marion Geidel, Barbara Adolphi, Stefan Schmult, and Thomas Mikolajick

J. Vac. Sci. Technol. B 31, 03C111 (2013); http://dx.doi.org/10.1116/1.4793764 (4 pages)

Online Publication Date: 27 February 2013

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Molecular beam deposited zirconium dioxide (ZrO2) was assessed as high-κ gate dielectric for future GaN based devices. To compare and study electrical and structural properties, thin ZrO2 films were deposited on three different substrates, n++-c-plane GaN, p-(100) Si, and TiN. The films were fabricated by electron beam evaporation from a single stoichiometric ZrO2 target. A substrate-independent phase transition from amorphous ZrO2 to the tetragonal/cubic phase was identified by gracing incidence x-ray diffractometry. Finally, monoclinic ZrO2 emerged with increasing film thickness. As found by x-ray photoelectron spectroscopy, ZrO2 formed an abrupt interface to both GaN and TiN without intermixture. Dielectric constants in the range of 14–25 were extracted from capacitance versus voltage measurements for as-deposited ZrO2 films. The leakage currents of ZrO2 on GaN resembled their counterparts on Si as well as on TiN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
77.55.dj For nonsilicon electronics (Ge, III-V, II-VI, organic electronics)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Surface properties of c-plane GaN grown by plasma-assisted molecular beam epitaxy

Grzegorz Cywiński, Robert Kudrawiec, Łukasz Janicki, Jan Misiewicz, Caroline Chèze, Marcin Siekacz, Marta Sawicka, Paweł Wolny, Michał Boćkowski, and Czesław Skierbiszewski

J. Vac. Sci. Technol. B 31, 03C112 (2013); http://dx.doi.org/10.1116/1.4793765 (5 pages) | Cited 1 time

Online Publication Date: 28 February 2013

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Two series of GaN van Hoof structures with different thicknesses of an undoped GaN cap layer were grown under metal-rich conditions by plasma-assisted molecular beam epitaxy. These were then investigated by contactless electroreflectance (CER) to study the Fermi-level position of the (0001) GaN surface after growth as well as after chemical treatment using Piranha solution. The first and second series of samples were grown on GaN/sapphire templates and high-pressure bulk GaN crystals, respectively. A clear CER resonance followed by Franz–Keldysh oscillations (FKOs) of various periods was clearly observed for both sample series before and after chemical treatment. The Fermi-level position of the GaN surface was determined from the analysis of FKOs related to the built-in electric field in the undoped GaN layer. For the as-grown GaN surface, the Fermi level was found to be located 0.42 and 0.57 eV below the conduction band in samples grown on GaN/sapphire templates and high-pressure bulk GaN crystals, respectively. For the Piranha-etched GaN surfaces, the Fermi level was pinned at almost the same energy (0.49 and 0.48 eV) in each of the two sets of samples. This means that this cleaning procedure, which is commonly used before device processing, is able to saturate the surface states at a certain level of Fermi-level pinning.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
68.55.ag Semiconductors
73.20.At Surface states, band structure, electron density of states
78.20.Jq Electro-optical effects
81.05.Ea III-V semiconductors

MBE growth of ZnCdSe/ZnCdMgSe quantum-well infrared photodetectors

Aidong Shen, Arvind Pawan Ravikumar, Guopeng Chen, Kuaile Zhao, Adrian Alfaro-Martinez, Thor Garcia, Joel de Jesus, Maria C. Tamargo, and Claire Gmachl

J. Vac. Sci. Technol. B 31, 03C113 (2013); http://dx.doi.org/10.1116/1.4794383 (3 pages)

Online Publication Date: 4 March 2013

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The authors report the growth of quantum well infrared photodetectors (QWIPs) made from wide band gap II-VI semiconductors. ZnCdSe/ZnCdMgSe QWIPs in both medium-wave infrared and long-wave infrared regions were grown by molecular beam epitaxy on InP substrates. High-resolution x-ray diffraction and photoluminescence measurements showed that the as-grown samples have high structural and optical quality. Spectral responses with peaks at 8.7 μm and 4.0 μm have been obtained.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
68.65.Fg Quantum wells
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.07.St Quantum wells
85.60.Gz Photodetectors (including infrared and CCD detectors)

In-rich InGaN thin films: Progress on growth, compositional uniformity, and doping for device applications

Mark A. Hoffbauer, Todd L. Williamson, Joshua J. Williams, Julia L. Fordham, Kin M. Yu, Wladek Walukiewicz, and Lothar A. Reichertz

J. Vac. Sci. Technol. B 31, 03C114 (2013); http://dx.doi.org/10.1116/1.4794788 (6 pages)

Online Publication Date: 8 March 2013

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A number of In-rich InGaN films with In contents in the 20–40% range have been grown at moderately low temperatures on sapphire and silicon substrates at high growth rates using a versatile molecular beam epitaxy-type technology that utilizes an energetic beam of N atoms called energetic neutral atom beam lithography and epitaxy to overcome reaction barriers in the group III-nitride system. Extensive characterization results on the crystalline, optical, and electrical properties of the In-rich InGaN materials are reported. It was found that N-rich growth conditions are required to produce materials that have excellent crystallinity, uniform compositions, and bright band edge photoluminescence. For In-rich InGaN growth on sapphire, electrical transport measurements show reasonably low carrier concentrations and high mobilities. Successful p-type doping of In-rich InGaN with ∼20% and ∼40% In contents is demonstrated, and preliminary results on the formation of a p–n junction are reported. For In-rich InGaN growth on Si, the film structural properties are somewhat degraded and carrier concentrations are considerably higher.
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68.55.ag Semiconductors
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors

GaSb-based infrared detectors utilizing InAsPSb absorbers

John F. Klem, Samuel D. Hawkins, Jin K. Kim, Darin Leonhardt, Eric A. Shaner, Torben R. Fortune, and Gordon A. Keeler

J. Vac. Sci. Technol. B 31, 03C115 (2013); http://dx.doi.org/10.1116/1.4794381 (7 pages)

Online Publication Date: 11 March 2013

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InPSb and InAsPSb have been investigated for use as absorber materials in GaSb-based n-type/barrier/n-type (nBn) detectors with cutoff wavelengths shorter than 4.2 μm. The growth temperature window for high-quality InPSb lattice-matched to GaSb by molecular beam epitaxy is approximately 440–460 °C. InPSb films with thicknesses greater than approximately 1 μm or films grown outside this temperature window have high densities of large defects, with films grown at lower temperatures exhibiting evidence of significant phase separation. In contrast, InAsPSb films can be grown with excellent surface morphologies and no apparent phase separation over a wide temperature range. InAsPSb samples with low-temperature photoluminescence between 3.0 and 3.4 μm and lattice mismatch of less than 1 × 10−3 have been grown, although both photoluminescence and x-ray diffraction data exhibit peak splitting indicative of compositional nonuniformity. AlAsSb-barrier nBn detectors with InPSb and InAsPSb absorbers have been fabricated. At 160 K, InPSb-absorber devices have a photocurrent responsivity edge at approximately 2.8 μm and a dark current of approximately 1.4 × 10−7 A/cm2, and InAsPSb devices with responsivity edges of 3.1–3.2 μm have a dark current of 2.3 × 10−8 A/cm2. Both InPSb and InAsPSb devices require significant reverse bias for full photocurrent collection at low temperature, suggesting the existence of an undesirable valence band energy discontinuity. The temperature dependence of dark current indicates that it is dominated by a mechanism other than generation in the undepleted absorber region.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth

Closed cycle chiller as a low cost alternative to liquid nitrogen in molecular beam epitaxy

Ryan B. Lewis, James A. Mackenzie, Thomas Tiedje, Daniel A. Beaton, Mostafa Masnadi-Shirazi, Vahid Bahrami-Yekta, Keelan P. Watkins, and Patricia M. Mooney

J. Vac. Sci. Technol. B 31, 03C116 (2013); http://dx.doi.org/10.1116/1.4795512 (6 pages)

Online Publication Date: 14 March 2013

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The high cost of cooling the cryoshroud in a molecular beam epitaxy system has been greatly reduced by replacing liquid nitrogen (LN2) as a coolant with a silicone polymer heat transfer fluid cooled to as low as −80 °C by a closed cycle chiller. Gallium arsenide epitaxial layers have been grown with two different cooling configurations of the shroud: conventional LN2 cooling and cooling to −70 °C with the chiller. The partial pressure of water in the chamber is a factor of about 2.5 higher with the closed cycle chiller operating at −70 °C than with liquid nitrogen in the shroud. No significant difference is observed in the density of deep levels in the GaAs, as determined by deep level transient spectroscopy.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Development of AlGaN-based graded-index-separate-confinement-heterostructure deep UV emitters by molecular beam epitaxy

Haiding Sun, Jeff Woodward, Jian Yin, Adam Moldawer, Emanuele F. Pecora, Alexey Yu. Nikiforov, Luca Dal Negro, Roberto Paiella, Karl Ludwig, Jr., David J. Smith, and Theodore D. Moustakas

J. Vac. Sci. Technol. B 31, 03C117 (2013); http://dx.doi.org/10.1116/1.4796107 (7 pages)

Online Publication Date: 21 March 2013

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The authors report on the growth, structure, and emission properties of AlGaN double heterostructures having a graded-index-separate-confinement-heterostructure design. These devices were grown on the Si-face of 6H-SiC substrates by plasma-assisted molecular-beam epitaxy. The active region of the device consists of 75-nm thick Al0.72Ga0.28N film, confined by two 50-nm thick compositionally graded AlxGa1−xN films (x = 1–0.8 and x = 0.8–1) and two AlN cladding layers. X-ray diffraction and transmission electron microscopy provide evidence that the compositionally graded AlGaN layer may also be serving as a strain transition buffer, by blocking threading defects in the vicinity of the AlN/AlGaN heterointerface. Polarization dependent photoluminescence studies indicate that the emission from these structures at 257 nm is transverse magnetic polarized. Simulation studies indicate that the vertical confinement of the optical mode in these structures is 32.5% and simulations of the band structure indicate the formation of a p-n junction resulting from polarization-induced doping. Electron-beam pumping of these structures provides evidence of the onset of stimulated emission at room temperature.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
68.55.ag Semiconductors

Epitaxial growth of ZnTe on GaSb(100) using in situ ZnCl2 surface clean

Chihyu Chen, S. J. Kim, X. Q. Pan, and Jamie D. Phillips

J. Vac. Sci. Technol. B 31, 03C118 (2013); http://dx.doi.org/10.1116/1.4796108 (4 pages)

Online Publication Date: 21 March 2013

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The epitaxial growth of high-quality ZnTe on GaSb substrates is demonstrated by molecular beam epitaxy without the use of a group-V beam flux or intermediate GaSb buffer layer. A reduced surface cleaning temperature is achieved using a combination of HCl etching prior to loading into the growth chamber and use of a ZnCl2 flux during the thermal clean step. This procedure results in a surface clean temperature of approximately 440 °C, in comparison to 500 °C for an as-received GaSb substrate, providing a means to achieve a clean GaSb surface for ZnTe epitaxy without the requirement for a group-V flux to stabilize the surface to prevent noncongruent sublimation of GaSb. The resulting ZnTe epitaxial layers demonstrate good surface morphology and structural properties based on Nomarski microscope images, transmission electron microscopy images of the ZnTe/GaSb interface, and x-ray diffraction measurements demonstrating a rocking curve with a full width at half maximum of 40 arc sec for the ZnTe (004) reflection.
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68.55.ag Semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.37.Lp Transmission electron microscopy (TEM)
68.35.bg Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Optimization of growth conditions of type-II Zn(Cd)Te/ZnCdSe submonolayer quantum dot superlattices for intermediate band solar cells

Siddharth Dhomkar, Igor L. Kuskovsky, Uttam Manna, I. C. Noyan, and Maria C. Tamargo

J. Vac. Sci. Technol. B 31, 03C119 (2013); http://dx.doi.org/10.1116/1.4797486 (7 pages)

Online Publication Date: 21 March 2013

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Intermediate band solar cells (IBSCs) have been predicted to be significantly more efficient than the conventional solar cells, but have not been realized to their full potential due to the difficulties related to the fabrication of practical devices. The authors report here on growth and characterization of Zn(Cd)Te/ZnCdSe submonolayer quantum dot (QD) superlattices (SLs), grown by migration enhanced epitaxy. These QDs do not exhibit formation of wetting layers, which is one of the culprits for the unsatisfactory performance of IBSCs. The ZnCdSe host bandgap is ∼2.1 eV when lattice matched to InP, while the Zn(Cd)Te-ZnCdSe valence band offset is ∼0.8 eV. These parameters make this material system an excellent candidate for a practical IBSC. The detailed structural analysis demonstrates that the process of desorption of Cd and the preferential incorporation of Zn facilitates the formation of unintentional strained ZnSe-rich layer at the QD-spacer interface. The growth conditions have been then optimized so as to obtain high crystalline quality lattice matched SL, by growing intentionally Cd-rich spacers, which strain balanced the SL. The excitation intensity dependent photoluminescence confirmed the type-II nature of these multilayer QD structures, which is expected to suppress nonradiative Auger recombination, and improve the carrier extraction process when implemented in an actual device.
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81.05.Dz II-VI semiconductors
88.40.hj Efficiency and performance of solar cells
88.40.jp Multijunction solar cells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots
73.21.La Quantum dots

Energy splitting of CdSe quantum dots induced by intense femtosecond laser excitation

Shengkun Zhang, Iosif Zeylikovich, Taposh Gayen, Robert Alfano, and Maria Tamargo

J. Vac. Sci. Technol. B 31, 03C120 (2013); http://dx.doi.org/10.1116/1.4797485 (4 pages)

Online Publication Date: 22 March 2013

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Microscopic photoluminescence (PL) spectra of self-assembled CdSe quantum dots (QDs) grown by molecular beam epitaxy were investigated under excitation of intense femtosecond laser. Two samples with different QD sizes were fabricated. One had a single layer of larger CdSe QDs while the other had three layers of smaller QDs. The second harmonic radiation at 420 nm obtained from a mode-locked tunable Ti-Sapphire laser was used as the excitation source. The laser power density was in the order of kW cm−2 and the peak power density was in the order of GW cm−2 for the 150 fs laser pulse with a repetition rate of 78 MHz. The intense femtosecond laser pulses generated strong surface acoustic waves and modulated energy bands of electrons and holes of CdSe QDs. Increasing of the laser power resulted in the PL peak of the CdSe QDs splitting into four peaks for both QD samples: two peaks shifted to a lower energy side and the other two shifted to a higher energy side. The strong strain fields led to the mixing of heavy-hole state and light-hole state in the quantum dots. The strain fields further modulated the energy bands of electrons and holes and produced splitting of both electron–heavy hole (e-hh) transition and electron–light hole (e-lh) transition. For the sample with a single layer of smaller QDs, the energy splitting for both e-hh and e-lh transitions reached 23.5 meV at a peak power density of 0.32 GW cm−2. For the sample with three layers of larger QDs, the energy splitting was 19.9 meV for e-hh transition and 17.9 meV for e-lh transition at a peak power of 1.1 GW cm−2.
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78.67.Hc Quantum dots
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.47.J- Ultrafast spectroscopy (<1 psec)
68.35.Iv Acoustical properties
73.21.La Quantum dots
78.55.Et II-VI semiconductors

Epitaxial growth of engineered metals for mid-infrared plasmonics

Stephanie Law, Lan Yu, and Daniel Wasserman

J. Vac. Sci. Technol. B 31, 03C121 (2013); http://dx.doi.org/10.1116/1.4797487 (6 pages)

Online Publication Date: 22 March 2013

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The authors demonstrate the ability of high-quality epitaxial InAs films to be used as wavelength-flexible, low-loss, engineered plasmonic metals across the mid-infrared spectral range. Films are grown by molecular beam epitaxy and characterized by Hall effect measurements, atomic force microscopy, and infrared reflection and transmission spectroscopy. The losses of our plasmonic material are studied as a function of InAs doping density, growth rate, buffer layer type, and substrate type. High growth rates are shown to be integral to obtaining films with low losses and doping densities approaching 1×1020 cm−3.
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68.55.ag Semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.uj III-V and II-VI semiconductors

High performance long-wave type-II superlattice infrared detectors

Arezou Khoshakhlagh, Linda Höglund, David Z. Ting, Cory J. Hill, Sam A. Keo, Alexander Soibel, Jean Nguyen, and Sarath D. Gunapala

J. Vac. Sci. Technol. B 31, 03C122 (2013); http://dx.doi.org/10.1116/1.4798485 (4 pages)

Online Publication Date: 3 April 2013

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The authors report on growth, material characterization, and device performance of infrared photodetectors based on type II InAs/GaSb superlattices using the complementary barrier infrared detector (CBIRD) design. In this paper, control steps for improvement of material quality in terms of surface, structural, and optical properties of infrared detectors grown at Jet Propulsion Laboratory are described. For a specific CBIRD studied, these quality control steps indicate high structural and optical quality of the grown material. Furthermore, single-element detector from the optimized growth conditions exhibit dark current density less than 1 × 10−5 A/cm2 at applied biases up to Vb = 0.36 V (T = 77 K), so this material can be utilized for focal plane arrays development.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Type-II InAs/GaSb strained layer superlattices grown on GaSb (111)B substrate

Elena Plis, Brianna Klein, Stephen Myers, Nutan Gautam, Thomas J. Rotter, Ralph L. Dawson, Sanjay Krishna, Sang Jun Lee, and Young Heon Kim

J. Vac. Sci. Technol. B 31, 03C123 (2013); http://dx.doi.org/10.1116/1.4798650 (6 pages)

Online Publication Date: 8 April 2013

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