bluuebunny/crossref_metadata_2025 huggingface dataset:
High Speed InAs/AlSb and In0.53Ga0.47As/AlAs Resonant Tunneling Diodes
Authors: Chow D. H. , Schulman J. N. , ÖZBAY E. , Bloom D. M.
Published: March 2011

We report a comparison of InAs/AlSb and In0.53Ga0.47As/AlAs resonant tunneling diodes (RTDs) for high speed switching applications. Theoretical simulations are performed for both heterostructure systems using a two band tunneling model, which includes the effects of strain and band bending. Experimental peak current densities are observed to agree well with the calculated values over the range 1×104 A/cm2 to 5× 105 A/cm2. In both types of structures, the maximum peak current density (directly related to switching speed) is determined by device heating. In this regard, InAs/AlSb RTDs are found to be slightly superior to In0.53Ga0.47As/AlAs RTDs due to the low contact and series resistances of InAs. However, higher peak-to-valley ratios and swing voltages are obtained in the In0.53Ga0.47As/AlAs devices up to their maximum attainable peak current density (3.1×105 A/cm2 in this study). Both heterostructure systems yield RTDs with estimated switching times near 1 ps.
GaAs Devices for Low Loss Power Rectification
Authors: Munukutla L. V. , Cheng S. H. , Anderson S. J.
Published: March 2011

High voltage GaAs Schottky rectifiers fabricated using vapor phase epitaxy have been observed to be an order of magnitude higher in switching speeds than silicon. Measured rectifier barrier heights deduced from the I-V and C-V plots were found to be in good agreement with previously reported values. Our experimental results show no correlation between the epilayer thickness and barrier height.
Selective Implantation Patterning and MBE Regrowth for Integration of Mm-Wave Application Heterojunction Devices
Authors: Brugger Hans , Wölk Claus , Müssig Harald
Published: March 2011

A technology based on a combination of selective implantation for lateral patterning and a following large area regrowth by molecular beam epitaxy (MBE) is introduced. The technology allows the monolithic integration of devices with different vertical layer sequences on s.i. GaAs substrates in a quasi planar way, e.g. a heterojunction field-effect-transistor (HFET) with a Schottky diode or a MESFET with a Schottky diode. Selective high resistive (>109 Ω/sq) and highly conducting (<20Ω/sq) buried layers are fabricated by high temperature stable oxygen and silicon implantation, respectively. The following MBE regrowth of epitaxial layers yields to an excellent surface morphology. HFET structures with pseudomorphic AlGaAs/InGaAs/GaAs heterostructures grown on implanted substrates exhibit a strong photoluminescence response. Carrier densities up to 2.0×1012cm−2 (1.6×1012cm−2) and Hall mobilities of 6150 cm2/Vs (17700 cm2/Vs) at 300 K (80 K) in the dark are achieved. The material quality is drastically improved by substrate preparation and in-situ cleaning prior to MBE regrowth.
(InAs)1/(GaAs)n Superlattice Quantum Well Lasers
Authors: Lopata J. , Dutta N. K. , chand Naresh
Published: March 2011

Strained layer In0.2Ga0.8As/GaAs quantum-well (QW) lasers have been used to pump Erbium Doped Fiber Amplifiers for use in opto-electronic communication systems. These InGaAs/GaAs Q-W lasers grown as graded index separate confinement heterostructures (GRINSCH) emit at 980 nm and have exhibited low threshold current densities, high electrical to optical power conversion efficiencies, low noise, and low temperature sensitivities [1–3]. Recently there has been much attention toward the growth and fabrication of devices containing short period superlattices of (InAs)m/(GaAs)m or (GaAs)m/(AlAs)n compositions [4–9]. Indeed the growth of inverted MODFET structures using a (GaAs)/(AlAs) superlattice barrier in place of an AlGaAs random alloy exhibited an increase in low temperature mobility due to reductions in the number of impurities and interface roughness [7]]. Can the optical properties of strained layer InGaAs/GaAs Q-W lasers also be improved by growing an (InAs)/(GaAs)4 short period superlattice as the active layer in place of the In0.2Ga0.8 As random alloy?

This paper reports the fabrication of ridge waveguide lasers using a 6 period (InAs)1/(GaAs)4 superlattice active region in a GRINSCH laser structure. One period of the superlattice consists of 1 monolayer (ML) of InAs and 4 ML of GaAs. Thus the average In composition in the superlattice is 20%. This superlattice laser is an alternative to the In0.2Ga0.8As/GaAs random alloy quantum-well laser used as a pump source for Erbium Doped Fiber Amplifiers. In a single quantum well In0.2Ga0.8As/GaAs laser the active region is a thin layer (-70Å thick) sandwiched between GaAs barrier layers. The superlattice active laser reported here has 6 periods of (InAs)1/(GaAs)4 as the light emitting region of a total width comparable to a single quantum well of random alloy composition.
Recent Developments in Gas Source Molecular Beam Epitaxy
Authors: Cunningham J. E.
Published: March 2011

We review Gas Source Molecular Beam Epitaxy of the GaAs/AlGaAs system. Among the growing number of condensed matter discoveries in materials grown by this approach we describe within resonant tunneling structures. This example serves to demonstrate the high quality quantum well formation and suppressed rate of dopant segregation that occurs during the GSMBE approach. We find a physical basis to quantify the latter growth effects when dopant segregation is viewed in two new ways. First, the broken translational symmetry created by the surface leads to dopant motion (as segregation) that otherwise is not allowed in the crystal interior (as diffusion). Secondly, dopants can dimerize on the crystal surface and this ultimately dictates how the rates of incorporation and segregation proceeds. The manner in which growth creates or destroyes covalent bonds of dopants on semiconductor surfaces thus presents new opportunities to improve dopant control.
The Negative Persistent Photoconductivity in the Deep Quantum Wells
Authors: Lo Ikai , Mttchel W. C. , Stutz C. E. , Yen M. Y.
Published: March 2011

We have measured the Shubnikov-de Haas effect and Quantum Hall effect on the AlxGa1−xSb/InAs quantum wells for the A1 composition (x) from 0.1 to 1.0 under the negative persistent photoconductivity (NPPC) conditions. It confirmed the prediction of ionized deep donor model that the NPPC effect is a general property for the materials containing ionized deep donors at low temperatures. The time-dependent recombination (electron capture) of the ionized deep donors has the similar property to that of DX centers. The saturated reduction of carrier concentration in the InAs well increases with increasing x, and rises steeply at about x=0.4. By comparing with the concentration of the DX center-like deep donor in the bulk AlxGa1−xSb, we believe that the ionized deep donors which cause the NPPC in the AlxGa1−xSb,/InAs QW's are the DX center-like deep donors in the AlxGa1−xSb layers.
The Structure of GaAs Grown by Chemical Beam Epitaxy on Low-Temperature Cleaned Silicon
Authors: Xing Y. R. , Kiely C. J. , Goodhew P. J.
Published: March 2011

Chemical beam epitaxy (CBE) has been used to grow GaAs on silicon with a low defect density after etching in HF followed by a low temperature (600°C) in situ heat treatment. High resolution electron microscopy (HREM) and convergent beam electron diffraction (CBED) studies show the presence of 90° and 60° dislocations and some inversion domains.
Cathodoluminescence Studies of Thermal Stress in Patterned GaAs/Si
Authors: Lingunis E. H. , Haegel N. M. , Karam N. H.
Published: March 2011

Thermal stress distributions in patterned GaAs/Si are studied by low temperature cathodoluminescence spectroscopy. The MOCVD-grown samples have ben patterned in the form of stripes either by selective etching or by selective GaAs/Si growth using a SiO2 mask. In this work, the relevant stress components are determined as functions of position for stripes with different width to thickness ratios from low temperature (10 K) GaAs cathodoluminescence spectra and the results are discussed in comparison with finite element elastic calculations.
Strain-Relieved Reliable Lasers Grown on Si By MOCVD
Authors: Egawa Takashi , Hasegawa Yoshiaki , Jimbo Takashi , Umeno Masayoshi
Published: March 2011

Conventional GaAs-based laser diodes grown on Si substrates suffer from rapid degradation, which results from the deteriorations of optical and electrical characteristics. Electroluminescence observation shows that the optical deterioration is caused by the formation of dark-line defects. The current-voltage (I-V) characteristic of the p-n junction is degraded with aging, and results in an ohmic-like under a higher ambient temperature and a larger forward current. The deterioration of the I-V characteristic is caused by defect-accelerated impurity diffusion because the growth of GaAs on Si substrates (GaAs/Si) involves the high dislocation density, the large tensile stress and the large amount of Si near the GaAs/Si interface. A significant improvement in reliability has been achieved in the strain-relieved AlGaAs/InGaAs laser diode on Si grown with the InGaAs intermediate layer. The stress relief by the InGaAs active layer and the reduction of the dark-line defect formation by the InGaAs intermediate layer are required to fabricate reliable GaAs-based laser diodes on Si substrates.
Optical, Electrical, and Structural Characterization of GaInAsP/InP Layers Grown on Silicon Substrate for 1.35 μm Laser Applications
Authors: Mobarhan K. , Jelen C. , Kolev E. , Razeghi M.
Published: March 2011

A 1.35 μm wavelength GaInAsP / InP double heterostructure laser has been grown on Si substrate by low-pressure metalorganic chemical vapor deposition. The layers are grown directly on Si substrate coated with GaAs. Material characterization confirms the overall quality of the epitaxial layers, including excellent crystallinity and optical properties in addition to precision control over the growth, composition and doping of the different layers. Pulsed operation with output power of over 200 mW per facet was achieved at room temperature for a broad area laser with 20 μm width and 170μm cavity length.
High-Quality InSb Growth on GaAs and Si by Low-Pressure Metalorganic Chemical Vapor Deposition
Authors: Choi Y. H. , Sudharsanan R. , Besikci C. , Bigan E. , Razeghi M.
Published: March 2011

We report the first InSb film growth on Si by low-pressure metalorganic chemical vapor deposition. High-quality layers of InSb have been grown on Si and GaAs substrates. InSb films displayed mirror-like morphology on both substrates. X-ray full width at half maximum of 171 arcsec on GaAs and 361 arcsec on Si for a InSb layer thickness of 3.1 μm were measured. Room-temperature Hall mobilities of 67,000 and 48,000 cm2/V.s with carrier concentration of 1.5×1016 and 2.3×1016 cm−3 have been achieved for InSb films grown on GaAs and Si substrates, respectively. A 4.8 μ-thick InSb film on GaAs exhibited mobility of 76,200 cm2/Vs at 240 K.
SiGe/Si-Bipolar and Quantum Well Transistors, Results and Prospects
Authors: KÖNIG ULF
Published: March 2011

The quality of SiGe/Si heterodevices recently could be improved by depositing on a SiGe buffer with a Ge grading. In house MBE grown structures reached 1.5 K mobilities of 173000 cm2/Vs. Also at room temperature (RT) the mobility is up to 4 times higher than in bulk Si or SiGe. HBTs in the discussed material system can exceed performances of conventional Si-homobipolar transistors, already with relaxed design rules. I briefly review on mesa - like SiGe HBTs with high fmax and fT around 50 GHz, owing to low base sheet resistances <1Kω□. In DC-operation high gains >400 or 13 000 at RT or 77K were obtained, n - and p - channel Si, SiGe and Ge MODFETs will be presented in more detail, n- MODFETs exhibit high transconductances above 300 mS/mm at RT and almost 1000 mS/mm at 77K. Different effects will be discussed, e.g. the influence of the gate to channel distance and effects of rapid thermal activation. Si/Ge heterosystems offer exclusive properties, e.g. the same mobility in a Si - 2DEG and a Ge - 2DHG. Complementary MODFETs (CMOD) can be envisaged. Furtheron the Si/Ge system allows the monolithic integration of heterodevices with high complexity Si - ICs (heterointegration).
Boron Diffusion in Si1−x Gex Strained Layers
Authors: Moriya N. , King C. A. , Feldman L. C. , Luftman H. S. , Green M. L. , Bevk J. , Weir B. E.
Published: March 2011

Boron diffusion in Sia7 Gea3 strained layers has been studied as a function of annealing temperature and is compared to boron diffusion in unstrained Si epitaxial layers. A lower diffusivity was observed in Sia7 Gea3 strained layers as compared to the Si control samples. Using the well-accepted model for boron diffusion via charged point defects in Si, the intrinsic diffusivities of the boron atoms in the Sia7 Gea3 layers were derived and an activation energy of 4.4 eV was estimated for the diffusion process.

A new approach to describe the diffusion process is also presented here. In this model, we relate the lower diffusivity to a corresponding change in the charged point defect equilibrium concentration caused by a change in band-gap due to the strain and the existence of foreign atoms in a Si matrix.
Raman Scattering Studies of Si1−xGex Layers Grown by Atmospheric Pressure Chemical Vapor Deposition
Authors: Perry C. H. , Lu Feng , Namavar F. , Rowell N. L.
Published: March 2011

Room temperature Raman spectra are reported of Si1−xGex layers on Si substrates (for 0.08≤x≤0.2). The samples were grown using atmospheric pressure chemical vapor deposition techniques. Layer thicknesses varied from 0.1 — 10μm. The relative frequency shift of the Si-Si phonon mode for the SiGe strained epilayers from an incommensurate pseudo-alloy of the same composition is used as a quantitative measure of the lattice strain. For thicknesses below a critical value the Raman data indicate that the films are highly strained and the growth is commensurate with the substrate whereas thicker films are partially or fully relaxed. Phonon lines are sensitive to the interfaces and alloy layers. The results are consistent with other characterization studies, such as TEM and X-ray rocking curve measurements, of the same samples.
Structural Investigation of Photoluminescent Porous Si by Transmission Electron Microscopy
Authors: Shih S. , Jung K. H. , Kwong D. L.
Published: March 2011

We have developed a new, minimal damage approach for examination of luminescent porous Si layers (PSLs) by transmission electron microscopy (TEM). In this approach, chemically etched PSLs are fabricated after conventional plan-view TEM sample preparation. A diffraction pattern consisting of a diffuse center spot, characteristic of amorphous material, is primarily observed. However, crystalline, microcrystalline, and amorphous regions could all be observed in selected areas. A crystalline mesh structure could be observed in some of the thin areas near the pinhole. The microcrystallite sizes were 15–150 Å and decreased in size when located further from the pinhole.
Sub-Micron Selective Photoluminescence in Porous Si by Focused Ion Beam Implantation
Authors: Steckl A. J. , Xu J. , Mogul H. C. , Mogren S.
Published: March 2011

The effect of Si doping on the formation of stain-etched porous Si and its photoluminescent properties was studied. Porous Si is obtained by purely chemical etching of crystalline Si in a solution of HF:HNO3:H2O in the ratio of 1:3:5. We have observed that an incubation time (ti) exists between the insertion of Si into the solution and the onset of porous Si production. This incubation time was found to be a strong function of hole concentration in both n- and p-Si. In p-Si, the ti decreased rapidly with increasing conductivity, whereas for n-Si the opposite (but not as pronounced) trend was found to be the case. For example in (B-doped) p-Si, ti, is only ∼0.5 min for 250 (Ω-cm)−1 but increases to ∼ 5 min for 0.2 (Ω-cm)−1. In (P-doped) n-Si substrates ti was ∼ 8 min for 0.2 (Ω-cm)−1 increasing to ∼ 10 min for 7 (Ω-cm)−1. Photoluminescence (PL) measurements of the porous Si obtained on substrates of various conductivity (p and n) show similar spectra, namely a peak at around 1.94 eV with a full width at half-maximum (FWHM) of about 0.5 eV. Based on the ti difference, we have fabricated localized photoemitting porous Si patterns by Ga+ focused ion beam (FIB) implantation doping and B+ broad beam (BB) implantation doping of n-type Si. Using 30 kV FIB Ga+ implantation, sub-micron photoemitting patterns have been obtained for the first time.
Luminescent Porous Silicon Investigated by accelerator analytics
Authors: Steiner Peter , Weidhaas Jens , Lang Walter
Published: March 2011

Electroluminescent nanoporous silicon is investigated by accelerator techniques. Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) are used to measure the oxygen content. The stoichiometry is Si1O1.8 in the top layer and Si1O0.8 in 6 μm depth. Channeling experiments show that only very weak channels are present.
Integrated Heterostructure Devices (IHDS): A New Approach for the Fabrication of High-Efficiency Blue/Green Light Emitters Based on II-VI Materials
Authors: Lansari Y. , Yu Z. , Ren J. , Boney C. , Cook J. W. , Schetzina J. F.
Published: March 2011

Integrated heterostructure devices (IHDs) comprised of II-VI materials in multi-layered structures for light emitting diode (LED) and laser diode (LD) applications are described. These IHDs combine a light emission multilayer structure (wide band gap II-VI layers) with an abrupt or graded heterostructure (comprised of narrow band gap II-VI layers) for improved ohmic contact to the upper p-type layer of the light emitting structure.
TEM Investigations of CdTe/GaAs(001) Interfaces
Authors: Angelo J. E. , Gerberich W. W. , Bratina G. , Sorba L. , Franciosi A.
Published: March 2011

In this study, cross-sectional transmission electron microscopy (XTEM) was used to investigate the defect structure which occurs at the interface between CdTe(001) and GaAs(001). The heterostructures were fabricated by molecular beam epitaxy on chemically etched and thermally deoxidized GaAs(001) substrates as well as GaAs(001) buffer layers grown in-situ by molecular beam epitaxy. This allowed for investigation of the GaAs surface preparation on the subsequent interfacial structure. The as-etched substrate led to a microscopically rough interface with the CdTe depositing in etch pits on the GaAs surface, while growth on the buffer layer led to a macroscopically flat interface. Further, growth was accomplished on different Te-induced surface reconstructions ((6×1) vs (2×1)) in an effort to understand the role of the precursor surface treatment on the subsequent interfacial structure. In this case growth on the (6×1) reconstruction led to the introduction of (111)-oriented inclusions at the interface, while the (2×1) reconstruction led to pure (001)-oriented growth. A mechanism for the formation of planar defects at the CdTe/GaAs(001) interface is described which is based on local misorientations of the CdTe and GaAs. Finally, preliminary results of ex-situ annealing experiments on the interfacial defect structure will be discussed.
CW Nd:YAG Laser Deposition of CdS Thin Films
Authors: Wang X. W. , Finnigan D. J. , Noble R. , Mattocks P.
Published: March 2011

There are two phases of CdS, wurtzite (hexagonal) and zincblende (cubic). To the best of our knowledge there is no report on the growth of large single crystal cubic CdS. Although there have been reports on the vapor deposition of cubic dominated CdS thin films, physical measurements were limited. Substrate material has been considered as the primary factor in attaining the cubic dominated CdS thin films. We report new results on CW Nd:YAG laser deposition of CdS thin films at various temperatures. X-ray diffraction patterns show that the films deposited at 200°C have a dominant cubic phase, those at 400°C being hexagonal. Optical transmission measurements reveal room temperature absorption edges of 515nm and 500nm for films deposited at 200°C and 400°C, respectively. Transmission electron microscopy further reveals differences in crystal structure of the two films. Raman spectra of the cubic film is similar to that of the hexagonal film.
Molecular Beam Epitaxy of PbTe/EuTe Superlattices
Authors: Springholz G. , Bauer G.
Published: March 2011

Using reflection high energy electron diffraction (RHEED), the heteroepitaxy of EuTe on PbTe (111) by molecular beam epitaxy (MBE) was investigated. The resulting EuTe (111) surfaces exhibit different surface reconstructions corresponding to a Te-stabilized or a Eu-stabilized surface. We have observed perfect 2D layer-by-layer heteroepitaxial growth and RHEED intensity oscillations only for a small range of growth conditions. Using such optimum conditions, we have fabricated strained PbTe/EuTe superlattices with superior structural perfection, as shown by high resolution x-ray diffraction.
Increase in Schottky Barrier Height in the CoSi2/Si (100) Interface Caused by Hydrogen
Authors: Marwick A. D. , Aboelfotoh M. O. , Casparis R.
Published: March 2011

It is shown that the presence of 8 × 1015 hydrogen atoms/cm2 in the CoSi2/Si (100) interface causes an increase in the Schottky barrier height of 120 meV, and that passivation of dopants in the substrate is not the cause of this change. The data is evidence that the position of the Fermi level in this interface is controlled by defect-related interface states. After hydrogenation the Schottky barrier height agrees with that predicted by theory for Fermi level pinning by virtual gap states of the silicon.
Passivation of Gaas by Novel P2S5/(NH4)2Sx Sulfurization Techniques
Authors: Hsieh J. T. , Sun C. Y. , Hwang H. L.
Published: March 2011

A new surface passivation technique using P2S5/(NH4)2S on GaAs was investigated, and the results are compared with those of the (NH4)2Sx treatment. With this new surface treatment, the effective barrier heights for both Al- and Au—GaAs Schottky diodes were found to vary with the metal work functions, which is a clear evidence of the lower surface state density. Results of I—V measurements show that P2S5/(NH4)2S—passivated diodes have lower reverse leakage current and higher effective barrier height than those of the (NH4)2Sx -treated ones. Auger Electron Spectroscopy, X—ray photoelectron spectroscopy and Raman scattering measurements were done to characterize the surfaces including their compositions and surface band bending. In this paper, interpretations on this novel passivation effect is also provided.
Optical Detection of Band Gap Variations Due to Ordering in Ga0.47In0.53As on InP
Authors: Arent D. J. , Bertness K. A. , Kurtz Sarah R. , Bode M. , Olson J. M.
Published: March 2011

A reduction in the optical energy gap of more than 65 meV has been observed in In0.53Ga0.47 As grown on (100) InP by atmospheric pressure metalorganic vapor phase epitaxy. The band gap energies were deduced from room temperature photocurrent spectroscopic measurements, accounting for differences in composition and strain. Spontaneous CuPt type ordering of In and Ga atoms on the (111) subplanes of the InGaAs2 was confirmed by transmission electron microscopy. Superlattice signatures in the transmission micrographs were observed only for samples with associated reduced band gap energies, and were confirmed by visible double periodicity in high resolution images. In0.53Ga0.47 As was grown under a variety of conditions, some which promoted ordering. In general, lower growth temperatures and moderate (∼4 μ/hr) growth rates promoted a greater degree of ordering and reduction of the band gap energy. The influence of growth conditions on the ordered structure is considered within the context of current theories.
A Tunable Schottky Barrier to n-GaAs Using Ni(Ga,Al) Contacts
Authors: Chen C-P. , Jan C-H. , Chang Y. A. , Kuech T.
Published: March 2011

The Schottky barrier heights of Ni(GaxAl1−x)/n-GaAs contacts have been measured by the I-V and C-V techniques. Contacts with x = 0.0, 0.25, 0.5, 0.75, and 1.0 have been prepared, and a wide range of Schottky barrier heights, 0.66 to 0.96 eV, can be achieved by varying the composition of the alloy contacts. After annealing at 400 °C, the barrier heights increase continuously from 0.66 to 0.96 eV as x decreases. The interfacial stability between the Ni(Ga,Al) contacts and GaAs has been examined by SAM. The modulation of the Schottky barrier height and the interface stability are explained by a thermodynamic and kinetic analysis of the GaAs-NiGa-NiAl-AlAs system.
The Study on the Pt Barrier Effect in Al/Pt/Ti/n-GaAs
Authors: Kuragaki T. , Hattori R. , Yajima K. , Sato K. , Takano H. , Otsubo M. , Mitsui S.
Published: March 2011

The degradation mechanism of the Schottky contact of Al/Ti/n-GaAs and Al/Pt/Ti/n-GaAs under the heat treatment of 300°C has been investigated. Barrier height of the Al/Ti/n-GaAs Schottky contact degrades drastically after the heat treatment, in which Ti-Al alloy and Ga out-diffusion have been observed. On the other hand, the barrier height of Al/Pt/Ti/n-GaAs contacts is stable under the heat treatment and, Al-Ti alloying as well as Ga out-diffusion in the metals could not be noticed. From these results, it is presumably concluded that the degradation of the Schottky contacts under the heat treatment is closely correlated with the Ga atom out-diffusion from GaAs surface into the metal films after Al-Ti alloy reach to the GaAs surface. The barrier height reduction after the heat treatment can be explained by the formation of the donor type level at the interface due to the Ga vacancy pile-up arose from the Ga out-diffusion. Pt layer was proved to be an effective barrier suppressing the intermetallic alloying and preventing out-diffusion of Ga.
The Effects of Growth Sequence on the Electronic Properties of Al-Ge-Ni Ohmic Contacts on (001) GaAs
Authors: Lampert W. V. , Haas T. W. , Lambers E. S. , Holloway Paul H.
Published: March 2011

The growth sequence of Al, Ge, and Ni metals was shown to dramatically affect the amount of heat treatment time required to convert the electrical properties from Schottky to ohmic behavior. Differences in the heat treatment times required to convert from rectifying to ohmic contact were dependent on the doping concentration of the contact layer and on the heat treatment temperature. Interdiffusion of component elements and phase formation have been studied to determine the origin of these effects. Auger depth profiles and X-ray diffraction have been used to determine the interdiffusion and phase formation resulting from various types of thermal processing. Elemental profiles and identification of phases of Ni-Ga, Ni-As, and Ni-Ga-Ge will be used to explain the origin of ohmic behavior.
Schottky Barrier Formation and Long Term Stability of Metal/N-Lnp Interfaces
Authors: Shi Z. Q. , Anderson W. A.
Published: March 2011

The formation of reliable high barrier height Schottky contacts to n-InP is essential for useful device fabrication. Fermi-level pinning traditionally has restricted the application of InP due to large reverse leakage current. Recently, we have proposed the enhancement of Schottky barrier heights (up to 0.98 eV) by deposition with the substrate cooled to low temperature (LT=77K) rather than at room temperature (RT=300K). Studies of the resistance of thin metal films during deposition reveals significant differences in metal nucleation for RT and LT diodes. For the long term stability study, a reverse bias of 2.0V was applied to both RT and LT diodes for more than 1500 hours. Then a constant forward current of 20 mA/cm2 was applied to the diode. The reverse current and forward voltage were recorded as a function of the testing time. After each step the saturation current density (Jo), barrier height (øB), and ideality factor (n) were measured using the current-voltage (I-V) technique. For a LT Au/n-InP diode, the Jo, øB, and n factor were found to be 3.4 × 10−11 A/cm2, 0.98 eV, and 1.31 before testing, and 4.8 × 10−10 A/cm2, 0.92 eV, and 1.31 after testing. The reverse leakage current was nearly constant during the testing. The forward voltage showed a little drop with time. The ultra-high øB and good stability of the LT diodes will be discussed in terms of the interface modification.
Study of Ohmic Contacts on P-Type ZnSe and ZnSe Epitaxial Layers Grown by Molecular Beam Epitaxy
Authors: Piskoti C. , Mykolajenko B. , Vaziri M.
Published: March 2011

To study the formation of ohmic contacts, several metals have been deposited on p-types ZnTe and ZnSe epitaxial layers. The metals were deposited on the layers either by simple evaporation or by electroplating. The current-voltage characteristics associated with each metal contact were measured. The preliminary results of these measurements indicate that electroplating is a better technique for making ohmic contact to these layers.
Growth and Device Applications of Epitaxial Insulators on Semiconductors
Authors: Ishiwara Hiroshi
Published: March 2011

Growth characteristics and device applications of heteroepitaxial insulator/semiconductor structures are reviewed. Discussions are made on both fluoride insulators such as CaF2, SrF2, BaF2, LaF3, CeF3, etc. and oxide insulators such as MgOAl2O3, CeO2, ZrO2, (Ba,Sr)O, SrTiO3, etc. First, the growth methods and typical results on the crystalline quality of the films are mainly discussed. In some cases, growth characteristics of semiconductor overlayers on the insulator / semiconductor structures are also discussed. Finally, applications of these structures to future electron devices are reviewed.
Growth and Characterization of Epitaxial BaF2 on InP
Authors: Jia Q. X. , Anderson W. A.
Published: March 2011

Epitaxial thin films of BaF2 were deposited for the first time onto (100) InP at a substrate temperature of around 450°C to 480°C by RF magnetron sputtering. The structural properties of the BaF2 film were a strong function of the substrate temperature during film deposition. X-ray diffraction analysis revealed a pure c-axis orientation perpendicular to the substrate surface. Scanning electron microscopy surface scan indicated a highly textured film with grid growth morphology. Ellipsometry measurement on the films gave a refractive index in the range of 1.4 to 1.6. The capacitance vs voltage analysis on a capacitor with a structure of Au/BaF3/InP demonstrated a dielectric constant of around 7.3 for the BaF2.
GaN/AlxGa1−xN Wurtzite Semiconductor Superlattices
Authors: Yuan Ren Shang , Dow John D.
Published: March 2011

A theory of electronic structures of NGaN×NAlGaN GaN/Alx Ga1−xN wurtzite semiconductor superlattices (grown in the direction of the c-axis) is developed and used to predict the superlattices' band structures, energy gaps, and the “deep” energy levels of substitutional s- and p-bonded defects in them. In addition, the valence band offset of GaN with respect to AlN, the one adjustable parameter of the theory, is determined to be about 0.4 times the total fundamental band-gap difference, by fitting the optical data for the superlattices' fundamental band gaps as a function of the layer thicknesses NGaN and NAlN, with the valence band edge of AlN being at lower energy.
Effects of Confinement on Shallow Impurities in GaAs-Ga 1−xA1xAs Quantum Dots
Authors: Osörio Francisco A. P. , HipöLito Oscar , Peeters Francois M.
Published: March 2011

The ground state energy of a shallow impurity placed in the center of a circular quantum dot is studied. The effects of the strength of the confinement potential and a perpendicular magnetic field are investigated theoretically.
Effects of Gamma-Ray Irradiation and Thermal Annealing on Characteristics of 3C-SIC MOS Structure
Authors: Yoshikawa M. , Morita Y. , Itoh H. , Nashiyama I. , Okumura H. , Misawa S. , Yoshida S.
Published: March 2011

Thermal annealing of interface traps introduced by 60Co gamma-ray irradiation in 3C-SiC metal-oxide-semiconductor (MOS) structures have been studied by high-frequency capacitance-voltage measurements. By isochronal annealing up to 400°C, two recovery stages were observed, which correspond to the annealing of two different types of the interface traps. It was found that introduction of the interface traps was suppressed by thermal annealing before irradiation. Radiation tolerance of 3C-SiC MOS structure is explained in terms of the room temperature annealing of the interface traps introduced by irradiation.
The Optical Properties of Plasma-Deposited SiO2 and Si3N4 Bragg Reflectors in the Spectral Range from 1.8 to 3.0 eV
Authors: Stephens D. J. , He S. S. , Lucovsky G. , Mkkelsen H. , Leo K. , Kurz H.
Published: March 2011

We have prepared 19-layer Si3N4:SiO2/…‥Si3N4:SiO2/Si3N4 (HL/HL/…HL/H), Bragg reflectors by remote plasma-enhanced chemical-vapor deposition, and have adjusted the constituent layer thicknesses to generate highly reflecting films over the entire visible spectrum from approximately 1.8 eV (∼690 nm) to 3.0 eV (∼410 nm). Peak values of the reflectance, in spectral bands with half-widths of ∼0.4 to 0.5 eV, are in the range of 96 to 98 %. The spectral response functions of these stacks exhibit departures from the optical behavior as calculated for exactly periodic structures with λ/4 layer thicknesses, and can be accounted for by taking into account: i) dispersion and absorption in the optical properties of the constituent layers; and ii) departures from the idealized and constant layer thicknessses.
The Effect of Quantum Well Structures on the Thermoelectric Figure of Merit
Authors: Hicks L. D. , Dresselhaus M. S.
Published: March 2011

Currently the materials with the highest thermoelectric figure of merit, Z, are Bi2Te3 alloys. Therefore these compounds are the best thermoelectric refrigeration elements. However, since the 1960's only slow progress has been made in enhancing Z, either in Bi2Te3 alloys or in other thermoelectric materials. So far, the materials used in applications have all been in bulk form. In this paper, it is proposed that it may be possible to increase Z of certain materials by preparing them in quantum well superlattice structures. Calculations have been done to investigate the potential for such an approach, and also to evaluate the effect of anisotropy on the figure of merit. The calculations show that layering has the potential to increase significantly the figure of merit of a highly anisotropic material like Bi2Te3, provided that the superlattice multilayers are made in a particular orientation. This result opens the possibility of using quantum well superlattice structures to enhance the performance of thermoelectric coolers.
Research needs in ARC Technology
Authors: Heberlein J. V. R.
Published: March 2011

The state of the art and the research needs of selected applications of arc technology are described. The selected applications include plasma torch design, plasma synthesis of materials, plasma chemical synthesis and metallurgical processing. The research areas where results can have the broadest impact on the technology are electrode effects, plasma fluid dynamics and non-equilibrium effects.
The Production of Metastable Metallic Particles Directly from the Mineral Concentrate By In-Flight Plasma Reduction
Authors: Moore J.J. , Reid K.J. , Sivertsen J.M.
Published: March 2011

Combining the reduction of the mineral oxide to a liquid metal and its rapid solidification provides an energetically favorable route tod provide metastable metallic particles or powders. Such an option is available with the Sustained Shockwave Plasma (SSP) reactor in which the mineral oxide is reduced using a carbon-based reductant within the plasma medium and subsequently rapidly solidified. This paper examines the degree of metastability of these metal particles using optical, electron and Auger microscopy and discusses the potential of this processing route.
The Effect of Structure on the Thermal Conductivity of Plasma Sprayed Alumina
Authors: Fiedler H.C.
Published: March 2011

Plasma sprayed deposits of alumina are normally of the metastable gamma phase, which transforms to alpha upon heating to an elevated temperature. The poor thermal conductivity of gamma phase is improved by transforming to alpha, but the improvement is restricted by the fragmented nature of the structure, a consequence of alpha being a denser phase than gamma.

Alpha phase has been reported to form when deposits are made on preheated substrates. It was found that reducing the distance between gun and deposition surface, thereby raising the temperature of the latter, resulted in transforming gamma to alpha, and as the temperature continued to rise, alpha formed directly from the liquid. The thermal conductivity of alpha formed directly from the liquid is 0.27 Watt/cm K at 323 K, which approaches the thermal conductivity given for 99.5% pure, 98% dense, polycrystalline alpha alumina.
An Experimental Study of Powder Melting During Low Pressure Plasma Deposition
Authors: Paliwal M. , Apelian D.
Published: March 2011

Low pressure plasma deposition (LPPD), a recent advancement in plasma spray metallizing, is currently being developed for high performance materials applications. An experimental study of particle melting within the plasma jet was pursued to identify the effect of the process variables and the material properties on the resultant deposit. In tandem the experimental results have been utilized in the development and verification of a mathematical model for the melting of powder particles during the process.

Two binary iron based model alloys - Fe-20 wt% Mn and Fe-20 wt% Cu - were plasma sprayed using Ma 2.4 and Ma 3 guns. Two different methods were used to evaluate the degree of particle melting within the plasma jet. The first method intercepts the particle path in the plasma jet with a glass slide, whereas in the second method the powder particles are collected in free flight using a powder collector (resolidification of powder particles occurs before they impact the collector walls). The droplets which impacted on glass slides and the collected (using the powder collector) powder particles were studied for mode and degree of powder particle melting using scanning electron microscopy. “Sweet spot” deposits (with no relative motion between the plasma gun and the substrate) were also made for the two model alloys in different size ranges using the Ma 2.4 and Ma 3 guns. The resulting deposits were metallographically evaluated. Mode and degree of particle melting injected under different process variables as well as the resultant deposit structures are presented.
Consolidation of Nickel Base Superalloys Powder by Low Pressure Plasma Deposition
Authors: Smith R.W. , Peterson L.G. , Schilling W.F.
Published: March 2011

Powder Metallurgy (P/M) technology has seen an important series of advances in the past twenty-five or so years. It has progressed from a press + sinter methodology (which still has important uses) to one of being a complete processing technology where, ultimately, the structure and properties of totally new materials can be synthesized. A key step in this evolution was the application of P/M techniques to high performance materials such as nickel-based superalloys. This effort began in the early 1960's and has resulted in several important
commercial applications such as P/M gas turbine disks and shafts.Attention has now turned to the potential use of Rapid Solidification Technology (RST) as a means of furthering the span of materials which can be made available for a wide variety of engineering applications. Rapidly solidified nickel, cobalt, titanium, aluminum and copper based materials are all the subject of extensive research and development at the present time (1).
Microstructure and Phase Composition of Sputter-Deposited Zirconia-Yttria Films
Authors: Knoll R.W. , Bradley E.R.
Published: March 2011

Thin ZrO2 -Y2 O3 coatings ranging in composition from 3 to 15 mole % Y2 O3 were produced by rf sputter deposition. This composition range spanned the region on the equilibrium ZrO2 -Y2O3 phase diagram corresponding to partially stabilized zirconia (a mixture of tetragonal ZrO2 and cubic solid solution). Microstructural characteristics and crystalline phase composition of as-deposited and heat treated films (1100°C and 1500°C) were determined by transmission electron microscopy (TEM) and by x-ray diffraction (XRD). Effects of substrate bias (0 ∼ 250 volts), which induced ion bombardment of the film during growth, were also studied. The as-deposited ZrO2-Y2O3 films were single phase over the composition range studied, and XRD data indicated considerable local atomic disorder in the lattice. Films produced at low bias contained intergranular voids, pronounced columnar growth, and porosity between columns. At high bias, the microstructure was denser, and films contained high compressive stress. After heat treatment, all deposits remained single phase, therefore a microstructure and precipitate distribution characteristic of toughened, partially stabilized zirconia appears to be difficult to achieve in vapor deposited zirconia coatings.
Non-Equilibrium Modeling and Dissipative Structures in Solid Material - Plasma Interactions
Authors: Khait Yu.L.
Published: March 2011

Topics discussed: (a) The dissipative structure (DS) composed of the plasma bulk (PB), near-to-surface plasma layer (PL), surface and the adjacent material layer (ML) coupled by mass, electric charge, etc. fluxes and applications to plasma deposition. (b) The transient local dissipative structure (TLDS) formed by a single plasma ion impinging on the surface and associated with sputtering, etc.
A Mass Spectrometric System for the Study of Transient Plasma Species in Thin Film Deposition
Authors: Johnson N.P. , Webb A.P. , Fabian D.J.
Published: March 2011

A system is described for mass spectrometric detection of transient gaseous species involved in reactive plasma deposition of materials. The equipment comprises a three stage differentially pumped UHV quadrupole mass spectrometer chamber, which permits modulated molecular beam sampling over a short path-length, direct from the plasma at 0.1–1.0 torr pressure. Operation of the system and optimum conditions for maximum signal-detection are detailed, and preliminary results for species formed in a silane-argon high-power rf discharge are reported. Spectra mostly agree with those obtained by Turban and Catherine using a lower power rf plasma, although some evidence is observed for the formation of increased SiH species at higher power.
Thermal Plasma Melting/Remelting Technology
Authors: Roman Ward C.
Published: March 2011

An overview is presented on several aspects of thermal plasma melting/remelting technology. Included is a brief description of the fundamentals of thermal plasma, basic types of plasma reactors, examples of unique configurations, highlights of some commercial applications, and recent state-of-the-art advances.
Plasmas in Extractive Metallurgy
Authors: Gauvin W. H. , Choi H. K.
Published: March 2011

It is becoming apparent that plasma technology will revolutionize certain of the conventional operations of extractive metallurgy. The use of plasma arcs in the iron and steel industry is already being demonstrated at powers up to 100 MW and these development will be briefly reviewed. In this connection, the advantages of plasma furnaces over electric furnaces are beginning to be well documented.

It is, however, in the area of the production of the refractory metals, such as molybdenum, zirconium, titanium, niobium, tungsten, tantalum, chromium and vanadium, that plasma technology offers unique opportunities as a result of advances in the design of transferred arc reactors. The work of the authors in this particular field will be described as well as other recent industrial developments.
Correlation of Electrical, Structural, and Optical Properties of Erbium In Silicon
Authors: Benton J. L. , Eaglesham D. J. , Almonte M. , Citrin P. H. , Marcus M. A. , Adler D. L. , Jacobson D. C. , Poate J. M.
Published: March 2011

An understanding of the electrical, structural, and optical properites of Er in Si is necessary to evaluate this system as an opto-electronic material. Extended x-ray absorption fine structure, EXAFS, measurements of Er-implanted Si show that the optically active impurity complex is Er surrounded by an O cage of 6 atoms. The Er photoluminescence intensity is a square root function of excitation power, while the free exciton intensity increases linearly. The square root dependence of the 1.54μm-intensity is independent of measurement temperature and independent of co-implanted species. Ion-implantation of Er in Si introduces donor activity, but spreading resistance carrier concentration profiles indicate that these donors do not effect the optical activity of the Er.
Er Luminescence in Si: A Critical Balance between Optical Activity and Pumping Efficiency
Authors: Coffa S. , Priolo F. , Franzó G. , Bellani V. , Carnera A. , Spinella C.
Published: March 2011

The several processes required to achieve Er luminescence in Si are investigated. In particular, the role of Er - O interactions to obtain the incorporation of high Er concentrations, electrically and optically active, in crystalline Si is investigated. It is found that a large enhancement in the electrical activation of Er (up to three orders of magnitude) is obtained by co-implanting Er with O at 573 K or at 77 K. However, the introduction of high concentrations of active Er in Si is not sufficient to obtain a large enhancement in the luminescence since an efficient pumping of the optically active sites is also required. The optical efficiency of this sample has been studied by photoluminescence. It is seen that an enhancement by a factor of ∼ 5 with respect to literature data is obtained. Moreover studies on the luminescence intensity as a function of the pump power gave important information on the mechanisms underlying Er luminescence in Si and its competing phenomena. These data are presented and discussed.
1.54 μm Photoluminescence of Erbium Implanted Hydrogenated Amorphous Silicon
Authors: Kechouane M. , Beldi N. , Mohammed-Brahim T. , L'Haridon H. , Salvi M. , Gauneau M. , Favennec P.N.
Published: March 2011

The luminescence of erbium implanted in hydrogenated amorphous silicon (a-Si : H) is presented. For the first time an intense and relatively sharp luminescence at 1.54 mm is observed in a-Si : H, using implanted erbium. The Er+ emission intensity strongly depends on the hydrogen film content and on the measurement temperature. A direct correlation between the optical gap energy of the semiconductor and the hydrogen film content is observed.
Electronic Properties and Their Relations to Optical Properties in Rare Earth Doped III-V Semiconductors
Authors: Taguchi Akihito , Takahei Kenichiro , Nakata Jyoji
Published: March 2011

We discuss the energy transfer mechanism between rare-earth 4f-shells and III-V semiconductor hosts. For Yb-doped InP, we have proposed an excitation and relaxation model, which explains experimental results for the electronic and optical properties. The Yb 4f-shell is excited by a recombination of an electron and a hole at an electron trap formed by Yb, which is located near the bottom of the conduction band of InP. At high temperatures, the relaxation energy of the Yb 4f-shell is back transferred as a host electron-hole pair, resulting in Yb luminescence quenching. We have found that Er-doped GaAs samples grown by metalorganic chemical vapor deposition contain as much C as Er. Rutherford back scattering and electronic property measurement results suggested that most of the Er atoms form complexes with C atoms, and these complexes are not electrically active. Such samples showed complicated Er 4f-shell luminescence spectra. To obtain a simple Er luminescence spectrum with a high peak intensity, O was intentionally doped with Er. Er-O complexes seemed to be formed in GaAs and these are responsible for simple and strong 4f-shell luminescence.