bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of The Transversal Electron Mobility in Heterojunction Bipolar Transistors with Strained SI1−x Gex-Base
Authors: Poortmans J. , Caymax M. , Van Ammel A. , Libezny M. , Nijs J.
Published: March 2011

The effective transversal mobility of the minority carrier electrons in asymmetrically strained p-type Si1−x Gex -layers, grown on a Si (100) substrate, is studied as a function of boron doping concentration and Ge-content x. The experiments are based on the temperature dependence (290 to 400K) of the collector current enhancement of heterojunction bipolar transistors with a pseudomorphic Si1−x Gex-base. The interpretation of these results is based on new insights about the effective density of states in the valence band of these strained layers [1]. We will present first experimental evidence of the theoretical calculations in [1]. From this we will derive then the value of the NcNv -product for the strained Si1−x Gex-alloy. This allows to extract the ratio of the electron mobility in Si and strained Si1−xGex. We found an enhancement of the mobility when the B-doping level is around 1018 cm−3 and 0.08<x<0.16. At higher values of the Ge-content and the doping level, the enhancement is reduced again.
Self-Compensation of Donors in GaAs Grown by MOCVD
Authors: Andreyev Gennady V. , Maslovsky Vladimir M.
Published: March 2011

The variation of luminescence parameters with the tin dopant concentration is considered in GaAs epitaxial layers. It is shown that at typical growth conditions and absence of contamination the deep accepters are generated by self material so that the compensation coefficient (K=Na/Nd) of 0.25 is constant up to critical electron concentration of 2.1018cm−3. The self-compensation is realized by native point defect ofattice which is gallium vacancy. The gallium vacancy is arranged next to the every fourth donor at the distance of 7 A.
Degradation and Recovery of Boron Doped Strained Silicon Germanium Layers After 1-MeV Electron Irradiation
Authors: Ohyama H. , Vanhellemont J. , Trauwaert M.-A. , Poortmans J. , Caymax M. , Clauws P.
Published: March 2011

1007×100 μm2 n+− Si/p-Si1−x Gex diodes fabricated on conventional p-type Si substrates are irradiated at room temperature with 1-MeV electrons with fluences from 1.0×1014 to 1.0×1015 e/cm2 in a high voltage transmission electron microscope. The boron concentration and germanium fraction of the Si1−x Gex epitaxial layer used for the diodes in this study are 5×1017 cm−3 and x = 0.12, respectively. The degradation of diodes is investigated by means of current/voltage and capacitance/voltage measurements. The characteristics of the electrically active defects induced in the Si1−x Gex epitaxial layer by irradiation are also examined by using deep level transient spectroscopy and capacitance/temperature measurements. The degradation of the diode performance and the presence of deep levels are investigated as a function of electron fluence. In order to examine the recovery process, an isochronal thermal anneal is performed in the temperature range between 100 and 400°C.
Thermal Stability of the Structural and Electronic Properties of Strain Symmetrized Sim Gen Superlattices and Ungraded, Nearly Relaxed Si1−x Gex
Authors: Dafesh P. A. , Adams P. M. , Arbet-Engels V. , Wang K. L.
Published: March 2011

In this study, photoreflectance (PR) spectroscopy and x-ray rocking curves measurements were used to study the variation in strain configuration, defect propagation, structural properties and direct electronic transition energies in Sim Gen superlattices (SL) and nearly relaxed Si1−x Gex buffer layers grown on < 100 > Si as a function of annealing temperature. The in-plane (a│) and perpendicular (a┴) lattice constants of the alloy buffer layers are found to vary only slightly with anneal temperature, TA, up to a temperature To. For TA To, the in-plane strain changed from roughly zero a│ ≈ a┴ (relaxed) or a┴ > a│ (compressive) to a┴ > a│ (tensile). This change in strain configuration is believed to be caused by the difference in thermal expansion coefficients between the epilayer and the Si substrate. The anneal temperature T0 is also correlated with the disappearance of higher order x-ray harmonics from the SL. This point was also correlated with a large energy shift and broadening of the PR spectra from the SL. The shift in energy of the PR spectra is explained in terms of the interdiffusion of Si and Ge at SL heterointerfaces, and to a lesser degree, the strain induced by the above mentioned difference in thermal expansion coefficients. The PR spectra of the alloy E0 transitions are also observed to shift to higher energy with increasing TA.
Broad Band vs Phonon Resolved Luminescence in Si1−xGex/Si Heterostructures Grown by Molecular Beam Epitaxy
Authors: Houghton D. C. , Rowell N. L. , Noel J.-P. , Dion M. M. , McCaffrey J. , Davies M. , Wang A. , Perovic D. D.
Published: March 2011

Si1−xGex alloys and multilayers synthesized by solid source MBE on Si(100) substrates have been characterized by low temperature photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Phonon resolved transitions originating from excitons bound to shallow impurities were observed in addition to a broad band of intense luminescence. PL spectroscopy over the temperature range 2K to 100K has been used to characterize Si1−xGex/Si heterostructures exhibiting both types of PL spectra. Thin alloy layers exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain and hole quantum confinement. In single quantum wells confinement shifts up to ∼200 meV were observed (1.2 nm wells with x = 0.38) and NP linewidths down to 1.37 meV were obtained. However, the broad PL band (peak energy ∼120meV below the strained bandgap) was predominant when the alloy layer thickness was greater than 2 – 10nm, depending on x, growth temperature, and substrate surface preparation. The strength of the broad PL band was correlated with the areal density of strain perturbations (∼109cm−2 per quantum well; local lattice dilation ∼1.5 nm in diameter) observed in plan-view TEM. The role of MBE growth parameters in determining optical properties was investigated by changing growth temperature, substrate preparation procedures and exploring the effect of surface passivation in a hydrogen ambient. In addition, post growth anneals at temperatures in the range 700°C to 1 100°C were carried out, where interdiffusion removes interfacial asperities and the broad luminescence band decays to zero intensity.
The Effects of Composition on the Spectral Loss Characteristics of SiGe Planar Waveguide Structures
Authors: Zuoya Yang , Weiss B. L. , Shao G. , Namavar F.
Published: March 2011

The effect of the Si:Ge ratio in SiGe/Si heterostructures on the structural and optical properties of SiGe/Si planar waveguide are reported here for Ge concentrations from 1 to 33.6%. The high propagation loss at 1.15 pm is due to band edge absorption, which increases as the Ge concentration increases, while the loss at longer wavelengths (1.523 pm) increases with decreasing Si concentration, due to the reduced optical confinement of the waveguide structure.
Atomic Oxidation of Ultra Thin SiGe Using Afterglow Oxygen Plasma
Authors: Chen P. C. , Lin J. Y. , Hsut Y. J. , Hwang H. L.
Published: March 2011

Microwave remote plasma oxidation system was used to study the oxidation of SiGe samples at low temperatures. The extent of Ge segregation at oxide/SiGe interface was investigated by using SIMS depth profiles. By comparing the segregation factors, the Ge segregation in the samples oxidized by atomic oxygen at 500 °C was much less than that in the samples oxidized without plasma at 950 °C. The Ge segregation has been largely suppressed by atomic oxygen oxidation at lower temperature.
Use of Valved, Solid Group V Sources for the Growth of GaAs/GaInP Heterostructures by Molecular Beam Epitaxy
Authors: Johnson F. G. , Wicks G. W. , Viturro R. E. , Laforce R.
Published: March 2011

We report on the first growth of GaAs/Ga0.5In0.5P heterostructures by conventional molecular beam epitaxy using solid-source valved crackers to supply both the arsenic and the phosphorus fluxes. By regulating the group V fluxes with the cracker needle valves, arsenide-phosphide heterostructures were successfully grown with virtually no group V intermixing between layers. For comparison, similar heterostructure samples were grown using only the mechanical shutters to switch between group V fluxes, and the resulting layers were severely intermixed. The amount of group V intermixing was shown to be independent of whether As2 or As4 fluxes were used to grow the layers. A GaAs/Ga0.5In0.5P multiple quantum well sample was also grown using the valved crackers. Photoluminescence peaks were clearly observed from 40 Å, 80 Å, and 300 Å GaAs quantum wells, but no luminescence was detected from a 20 Å well. An 80Å GaAs/ 80Å Ga0.5In0.5P superlattice was grown, and superlattice satellite peaks were observed in the X-ray rocking curves. The appearance of misfit dislocations suggests localized intermixing at the interfaces.
Production of GexSi1−x, and SiC Films on Si Substrates Using Particle-Beam Technologies
Authors: Kagadey V. A. , Ladizhensky O. B. , Lebedeva N. I. , Matin E. N. , Proskurovsky D. I. , Yakovleva L. V. , Zaporozhchenko V. I.
Published: March 2011

The paper presents the results of preliminary experiments on the production of GexSi1−x/Si structures using deposition of a thin Ge film on a Si substrate, implantation of Si ions and rapid electron-beam annealing. The conditions under which monocrystalline layers form have been found. It is supposed that the large depth of Ge penetration into Si is due to enhanced diffusion of Ge conditioned by the high density of point defects in the doped Si. It has been established that high-dose implantation of C ions into Si and subsequent electron beam annealing result in the formation of a monocrystalline layer of the SiC phase in the case of pulsed (∼0.7 μs) heating and liquid-phase recrystallisation and a polycrystalline SiC layer in the case of prolonged annealing.
Fabrication Process of Porous Silicon-Based Optoelectronic Devices
Authors: Kalkhoran Nader M.
Published: March 2011

A patterning process compatible with conventional Si electronics technology, which has resolution better than 5 μm, has been developed in order to perform selected-area anodic etching for producing luminescent porous Si layers (PSL). Correlations between the anodic etching and photolithographic parameters have been identified, and their effects on the resolution and luminescence of porous Si layers have been studied. Finally, the first monolithic processing, i.e.,. true wafer-scale integration, of a Si-based visible light-emitting diode (LED) and a photodetector using conventional Si technology has been demonstrated.
VUV- and Soft X-Ray-Induced Optical Luminescence and X-Ray Absorption Fine Structures of Porous Silicon
Authors: Sham T. K. , Jiang D. T. , Coulthard I. , Lorimer J. W. , Feng X. H. , Tan K. H. , Frigo S. P. , Rosenberg R. A. , Houghton D. C. , Bryskiewicz B.
Published: March 2011

Optical luminescence in porous silicon induced by soft X-ray and vacuum UV excitation with energies in the vicinity of the Si K-edge (1838 eV) and the Si L-edge (99 eV) has been observed. The luminescence has been used, together with total electron yield, to record X-ray absorption fine structure (XAFS) in the near-edge region of both Si edges. The near- edge spectra recorded simultaneously with either luminescence or total electron yield were compared, and the implications of these measurements for the structure of porous silicon are discussed.
Blue II-VI laser Diodes and light Emitting Diodes
Authors: Gunshor R. L. , Nurmikko A. V. , Otsuka N.
Published: March 2011

The use of a nitrogen rf plasma source for p-type ZnSe grown by MBE, has allowed a variety of pn junction based devices to be realized. The pn junctions have been combined with (Zn,Cd)Se quantum wells to implement semiconductor injection lasers, operating in the blue/green portion of the spectrum, which were reported by 3M and the Brown/Purdue group in the summer of 1991. In the past year the field has moved rapidly. In particular, we can now report CW operation at low temperatures as well as pulsed operation at room temperature (490nm) using a Zn(S,Se)-based device configuration. Laser power output per facet for some designs is above 300 mW, and threshold current densities are as low as 1000A/cm 2 at room temperature. Lasing was demonstrated from devices grown on both p and n-type GaAs substrates. X-ray rocking curves of theII-VI regions exhibit FWHM values below 20 arcsec for specific samples. Dislocation densities are less than 105 cm−2, below the threshold of TEM plan view imaging. The blue LEDs provide power outputs in excess of 100μW while exhibiting external quantum efficiencies of 0.1% at room temperature.
Blue Lasers Based on II-VI Semiconductor Heterostructures
Authors: Yu Z. , Ren J. , Lansari Y. , Gossett K. J. , Sneed B. , Bowers K. A. , Cook J. W. , Schetzina J. F.
Published: March 2011

Properties of blue laser diodes based on ZnSe-related II-VI semiconductor heterostructures are reported. At 77 K, continuous-wave (cw) operation has been achieved for lasers emitting at wavelengths as short as 470.4 nm (2.635 eV), while pulsed laser emission has been observed up to ∼200 K, for samples with uncoated facets. Measured turn-on voltages for stimulated emission at 77 K were as low as 12 V for some of the laser diodes due to improved ohmic contacts. For some particular devices, differential quantum efficiencies as high as 36% per (uncoated) facet have been obtained at 77 K.
“On the Growth - and Annealing - Temperature Dependence of the Electrical Properties of Ga0.51In0.49P/GaAs Heterostructures Grown by Mombe”
Authors: Paloura E. C. , Ginoudi A. , Frangis N. , Christou A.
Published: March 2011

We study the effect of growth temperature (TG) and post-growth rapid thermal annealing (RTA) on the electrical properties of Schottky diodes fabricated on undoped, lattice-matched Ga0.51In0.49P/GaAs heterostructures. The samples were grown by metalorganic molecular beam epitaxy (MOMBE) in the temperature range 480 – 560°C. Ga0.51In0.49P grown in this temperature range undergoes spinodal decomposition, as shown by cross-section TEM analysis. The dislocation-free epilayers grown at TG≤520°C are characterized by a deep electron trap with an activation energy of 800meV while growth at higher temperatures renders trap-free films. Furthermore, the Schottky barrier ideality factor (n) depends strongly on TG and takes the best value of 1.4 for TG=540°C, while the barrier height remains nearly constant at about 0.75eV. Finally, upon capped rapid thermal annealing the value of n improves while the trap concentration decreases significantly. Based on the presented experimental evidence we can propose that MOMBE growth at 540°C renders films with improved electrical properties.
Spectroscopic Investigation of Li and P-Doped ZnSe Grown by Molecular Beam Epitaxy
Authors: Zhang Y. , Skromme B. J. , Cheng H.
Published: March 2011

A conduction band-to-acceptor (e-A°) peak at 2.7060 eV has been identified for the first time in 1.7 K PL spectra of Li-doped ZnSe/GaAs. Photoluminescence (PL) measurements as a function of temperature and excitation level have been employed to confirm the identification and to study the behavior of this peak. This peak was previously misidentified as the “R”-band characteristic of bulk material, which has been associated with transitions between preferentially paired interstitial Li donors and substitutional Li acceptors on Zn sites. We find no direct evidence of Li interstitials in the PL data. The splitting of the Li acceptor-bound exciton is dramatically reduced by removal of the GaAs substrate, which proves that the splitting is due to strain and not to the hole-hole exchange interaction. A P-doped ZnSe/GaAs sample exhibits a shallow P bound exciton peak nearly superimposed on the donor-bound excitons. It is distinguished by its strong LO phonon replica and low energy undulation wing, which are both unique characteristics of shallow acceptor-bound excitons. Transitions involving the conduction band to split P acceptor light and heavy hole levels have been detected for the first time in P-doped heteroepitaxial ZnSe. Using the temperature dependence of the (e-A°) peak positions, accurate binding energies of 89.1±0.6 and 114.4±0.4 meV have been obtained for shallow P and Li acceptor levels in unstrained ZnSe, respectively
Growth and Optical Characterization of ZnMnTe Grown by Molecular Beam Epitaxy
Authors: Reno John L. , Jones Eric D. , Venturini Eugene L.
Published: March 2011

We have successfully grown ZnMnTe alloys by molecular beam epitaxy using GaAs as a substrate. Bulk MnTe has the wurtzite crystal structure but the structural phase of the material was confirmed to be zinc-blende by standard θ-2θ x-ray diffraction techniques. The composition was also determined using x-ray diffraction techniques. Manganese cancentration was also estimated from magnetization measurements taken as a function of temperature. Magneto-luminescence studies were performed at 1.4K on the acceptor-bound exciton in the semimagnetic semiconductor ZnMnTe alloys. As expected, the photoluminescence peak energy decreased with increasing magnetic field.
Interface Characterization of PbTe/BaSi/Si Heterostructures Grown Using MBE
Authors: Santiago F. , Woody D. , Chu T. K. , Huber C. A.
Published: March 2011

A new substrate material consisting of a buffer layer of a Ba-Si compound was developed by making use of the chemical reaction between BaF2 and Si. This substrate is very promising for the integration of IV-VI semiconductor materials with silicon. PbTe films of excellent quality, as determined by X-ray and Reflected High Energy Electron Diffraction spectra, have been deposited over (111)- and (100)-oriented silicon wafers of 3 inch diameter. These PbTe films are (100)-oriented irrespective of the Si orientation. X-ray photoelectron spectroscopy studies reveal very interesting chemistry at the interface between Ba-Si and Te. They suggest that BaTe may form between PbTe and Ba-Si at their interface. This interfacial region, which is of the order of only a few molecular layers, appears to be critical in the success of the deposition. Thermal cycling showed that the PbTe/BaSi/Si system is mechanically very stable. The possibility of a similar growth mechanism for the deposition of II-VI semiconductors such as CdTe is considered.
The Fabrication of NiSi2/Si(100) Interfaces with Controlled Morphologies
Authors: Sullivan J. P. , Tung R. T. , Schrey F. , Graham W. R.
Published: March 2011

The morphology and defect structures associated with thin NiSi2 films prepared on Si(100) were investigated. Facets were found to be a common defect structure at the interface unless stoichiometric co-deposition of Ni and Si was performed. Annealing thin, uniform NiSi2 layers prepared by stoichiometric co-deposition to temperatures ≥ 700°C yielded epitaxial films of high crystalline perfection. Films in which the deposition was off-stoichiometric exhibited a variety of defect structures. In addition to facets at the interface, networks of meandering micro-twins or stacking faults were observed in highly Ni-rich films, while pinholes were observed in Si-rich films. Facets at the interface were found to be eliminated by annealing at temperatures ≥ - 750°C, indicating that the planar NiSi2/Si(100) interface is energetically stable with respect to the formation of NiSi2(111) facets. Through manipulation of the film growth kinetics, NiSi2/Si(100) interfaces with arbitrary facet densities were produced. Partially faceted NiSi2/Si(100) interfaces represent ideal experimental systems for revealing the effects of Schottky barrier inhomogeneity on the electrical measurements of metal/semiconductor contacts.
Electrical Contacts to Metastable GexSi1−x Using Pd2Si as a Transport Layer
Authors: Purser Richard G. , Strane Jay W. , Mayer James W.
Published: March 2011

The transport of germanium through a co-deposited palladium-silicon layer on epitaxially grown GexSi1−x on Si(100) was studied. The Ge concentration in the UHV-CVD grown GexSi1−x film was x=.14 with a thickness of 155 nm. When the co-deposited layer is Pd rich with respect to Pd2Si, Ge was found to move through the Pd-Si layer and grow polycrystalline on the GexSi1−x. Ge transport and Pd2Si(111) grain growth ceased simultaneously. No transport was found for Si rich Pd-Si layers. Electrical characterization showed the contacts were ohmic with a specific contact resistivity between 6–12 μωQ-cm2 and an end resistance of.75 ω, resulting in a carrier concentration under the contact of 1.5×1014 cm−2. Hall effect measurements of the semiconductor gave n=5.77×1014 cm−2 and μ=36.96 cm−2/Vs. The sheet resistance of the contact layer was found to be 23.54 ω/square and the semiconductor was 237 ω/square.
Beem Investigation of Oxide and Sulfide Passivated GaAs
Authors: Alec Talin A. , Stanley Williams R. , Kavanagh Karen L.
Published: March 2011

Ballistic Electron Emission Microscopy (BEEM) was used to investigate the effects of a sulfide interfacial layer on the electronic properties of the Au/n-GaAs interface. Two diodes were simultaneously prepared in UHV by evaporating Au onto (100)GaAs substrates which were either treated with (NH4)2S or NH4OH etching solutions prior to Au deposition. Auger electron spectroscopy was used in situ to monitor the surface chemical composition. The effective Schottky barrier (SB) height was measured with BEEM at 10 different locations on the surface of each diode. The (NH4)2S treatment increased the average barrier height and reduced the spread in the values, as compared to the contact formed on the NH4OH treated GaAs.
Formation and Electronic Structure of the Mn/GaAs(100) Interface
Authors: Jin X. , Zhang M. , Dong G. S. , Li Z. S. , Wang Xun , Zhu X. G.
Published: March 2011

Formation and electronic structure of the Mn/GaAs(100) interface grown at room temperature are studied by photoemission. The growth at early stage is identified to be in two-dimensional mode. The chemical reaction and the interface diffusion happened between Mn and GaAs are explored in some details. A ferromagnetic phase of Mn overlayer at early stage is deduced from the change of electron density of states near the Fermi edge.
Microstructure Analysis of Thermally Stable Ohmic Contact to Both n and p+-GaAs
Authors: Han W. Y. , Lee H. S. , Lu Y. , Cole M. W. , Casas L. M. , DeAnni A. , Jones K. A. , Yang L. W.
Published: March 2011

A thermally stable Pd/Ge/Ti/Pt/ ohmic contact with low specific contact resistance was formed on both n and p+-GaAs. The lowest specific contact resistances were 4.7×10−7 and 6.4×10−7 Ω.cm2 for the n and p+-GaAs, respectively, when the n-GaAs was doped with Si to 2×1018cm−3, and the p+-GaAs was doped with carbon to 5×1019 cm−3. Interfacial reactions and element diffusions of the contacts were investigated by using transmission electron microscopy, Auger electron spectrometry with depth profiles. All the contacts were thermally stable at 300 °C for 20 hours, and it appeared that the p-contacts were more stable than the n-contacts.
Growth and Doping of GaN Films by ECR-Assisted MBE
Authors: Moustakas T. D. , Molnar R. J.
Published: March 2011

We report on growth, doping, and characterization studies of GaN films produced by the Electron Cyclotron Resonance microwave plasma assisted Molecular Beam Epitaxy. The films were grown heteroepitaxially on sapphire (0001), whose surface was converted into atomically smooth AIN by plasma nitridation. The GaN films were grown in two temperature steps, a process found to promote the layer-by-layer growth mode. ECR plasma conditions to grow either n-type autodoped or semi-insulating GaN film were identified. The structure and microstructure as well as the electrical properties of these two classes of films are discussed. A systematic dependence between electron mobility and net carrier concentration was found, which predicts that the mobility of GaN with a net carrier concentration of 1014cm−3 is about 104cm2 /V.s. The insulating films were intentionally doped either p-type or n-type by incorporation of Mg or Si during film growth. Hole or electron concentrations at 300K between 1018-1019cm−3 have been obtained without requiring any post-growth treatment.
High Mobility GaN films Produced by ECR-Assisted MBE
Authors: Molnar R. J. , Lei T. , Moustakas T. D.
Published: March 2011

High electron mobility autodoped GaN films were produced by the ECR assisted MBE method. The net electron concentration was varied systematically from 2×1019 to 2×1017cm−3 by controlling the active nitrogen overpressure. Correspondingly, the electron mobility increased from 20 to 210 cm2V−1sec−1. The line through the experimental data also predicts the electron mobilities of GaN films produced by the CVD methods.
GaN-AlxGa1−xN Heterostructures Deposition by Low Pressure Metalorganic Chemical Vapor Deposition for Metal Insulator Semiconductor Field Effect Transistor (Misfet) Devices
Authors: Asif Khan M. , Kuznia J. N. , Bhattarai A. R. , Olson D. T.
Published: March 2011

In this paper we report the fabrication and characterization of a metal insulator semiconductor field effect transistor (MISFET) based on single crystal GaN-AlxGa1−xN heterostructures. The device structure layers were deposited over sapphire substrate using low pressure metalorganic chemical vapor deposition. We discuss the fabrication and characterization of MISFET devices using single crystal GaN as the insulator layer. These were fabricated on isolated mesas using TiAu for the source and drain ohmic contacts and silver for the gate Schottky. For devices with a gate length of 4 μm (channel opening i.e. source to drain separation of 10 μm), a transconductance of 20 mS/mm was obtained at -1 volt gate bias. Complete pinchoff was observed for a gate potential of -15 volts. Device performance is compared to that for a GaN MESFET of identical dimensions.

Due to its direct bandgap tunable from 3.4 to 6.2 eV AlxGa1−xN is an important semiconductor for devices in the ultraviolet and visible parts of the spectrum. The large bandgap, potential of heterojunction formation and the insulating nature of AlN make AlxGa1−xN an ideal material system for high performance metal semiconductor field effect transistor (MESFET) devices requiring high operation temperatures. Availability of the insulator (single crystal AlN or GaN) also makes possible the fabrication of metal insulator field effect transistor (MISFET) devices which has been an elusive goal for the GaAs based III-V materials technology.

High quality single crystal GaN films have been deposited on sapphire and several other semiconductor substrates using metalorganic chemical vapor deposition (MOCVD)1,2, molecular beam epitaxy (MBE)3 and vapor phase epitaxy (VPE)4. Recently we have reported on quantum confinement5, room temperature stimulated emission6, and 2-dimensional electron gas in GaN-AlxGa1−xN heterostructures7,8. We have also deposited single crystal insulating GaN and A1N over sapphire using atomic layer epitaxy9,10 and fabricated high responsivity photoconductors11. We now report on the fabrication and characterization of FET devices using single crystal GaN-AlxGa1−xN heterostructures. This forms the basis of high temperature transistor devices based on the AlxGa1−xN material system.
Electronic Structure of Wide-Band-Gap Chalcopyrites
Authors: Petukhov A. , Lambrecht W. R. L. , Segall B.
Published: March 2011

Electronic band structures, equilibrium lattice constants and structural parameters, cohesive energies, and bulk moduli calculated by means of the linear-muffin-tin orbital method are presented for BeSiN2, MgSiN2 and MgSiP2 chalcopyrites. The relationships of these compounds to the “parent” III-V compounds are clarified.
Growth and Characterization of Layered Structures of Silicon Carbide and Aluminum Nitride
Authors: Sywe B. S. , Yu Z. J. , Edgar J. H. , Chaudhuri J.
Published: March 2011

Heterostructures of SiC and AlN in either sequence, AlN on SiC or SiC on AlN, were grown on Si, Al2O3, and 6H-SiC substrates by (metalorganic) chemical vapor deposition (CVD). On Si substrates, a SiC layer was first grown by a two-step technique and an AlN layer was deposited subsequently. On other substrates, an AlN layer was first grown, followed by SiC deposition. Multi-layered structures (SiC/AlN/SiC) were also produced to demonstrate the ability of heteroepitaxy of SiC and AlN on each other.

AlN grown on 3C-SiC were highly oriented polycrystalline films. AlN films on 6H-SiC, SiC films on A1N/Al2O3, and SiC films on AlN/6H-SiC were single crystal. In the latter two cases, the SiC films were in hexagonal structure. These SiC films were smooth and specular in appearance and showed n-type conductivity.
Optical Characterization of Amorphous SiNx:H Films Prepared by Plasma-Enhanced CVD
Authors: Tsai Rung-Ywan , Kuo L. C. , Ho F. C.
Published: March 2011

Amorphous SiNx:H thin films were prepared by plasma-enhanced CVD process. The effects of preparation conditions on the optical properties, compositions, and deposition rates of a-SiNx:H films were systematically studied by means of spectrophotometer, ellipsometer, and infrared spectroscopy measurements. It has been found that the refractive indices decrease with increasing the NH3 gas flow rate and the rf power, and increase with increasing the electrode spacing. Conversely, the deposition rates increase with increasing the NH3 gas flow rate and the rf power, and decrease with increasing the electrode spacing. There was no obvious effect of substrate temperatures ranging from 250 to 320°C on the optical properties and deposition rates of a-SiNx :H films. The decrease of the refractive index and the increase of the deposition rate were due to the increase of the nitrogen composition x occurring in the a-SiNx:H films. Refractive indices n and extinction coefficients k of a-SiNx:H films can be varied from n = 3.6 and k = 0.1 for x = 0 (pure a-Si:H) to n = 1.8 and k = 0 for x = 1.33 (pure a-Si3 N4:H) at the wavelength of 633 nm.
Chemically Modified Second Harmonic Generation at Surfaces on Vicinal Si(111) Wafers
Authors: Emmerichs U. , Meyer C. , Leo K. , Kurz H. , Bjorkman C. H. , Shearon C. E. , Ma Y. , Yasuda T. , Lucovsky G.
Published: March 2011

Using surface second harmonic generation (SSHG) at 1053nm, we study the influence of off-axis orientation and surface structure of silicon (111) surfaces. We study wafers cut at angles between 0° and 5° in the [112] direction. The surface structure is varied by thermal oxidation at 850°C, annealing, and thinning the oxide in a HF solution. For comparison, nitride films are also investigated. The characteristic rotational symmetry of the SSHG-signal for (111) flat (non-vicinal) surfaces is enhanced by a Si/SiO2 interface. The oxide layer also influences the signals due to the steps on vicinal surfaces. The results are discussed in comparison with a microscopic model of the oxidized misoriented surface.
Blue Shifting the Excitonic Transition in Multiple Quantum Wells by Rapid Thermal Processing
Authors: Malin Jay I. , Hsieh K. C.
Published: March 2011

Silicon doped multiple quantum well (MQW) detector structures were rapid thermally processed (RTP) for the purpose of blue shifting the excitonic transition. Structures were encapsulated with Sio2 prior to the anneal as such enhanced the degree to which interdiffusion occurred within the structure. This further lead to a blue shift in the exciton energy corresponding to the n=l transition which was observed by photoluminescence (PL) measurements. Having examined the PL spectra of various SiO2 encapsulated samples and performing variable intensity PL measurements, a peak corresponding to a defect at ∼ 80meV above the valence band was further observed. In addition, a variation in the degree to which disordering occurs has been observed under various physical conditions including doping and GaAs capping.
Studies of Interface Formation and Its Influence on Optical Properties of GaInAs/InP QW Structures
Authors: Seifert W. , Liu X. , Samuelson L.
Published: March 2011

It is a well-known phenomenon that the luminescence energies of nominally n monolayer (1 ML = 0.239 nm) thick QWs of GalnAs in InP are shifted to longer wavelengths in comparison to calculated values. The reason is seen in the formation of (Ga)InAs(P)-interfaces, one or a few ML thick, which contribute to the effective potential of the QW.Based on a comparison of MBE and MOVPE and on properties of QW structures grown by MOVPE under different conditions we conclude that high AsH3 pressures and low growth temperatures favour the formation of arsenic multilayers on the surface, which act as the main arsenic source for the formation of graded InAsxP1−x interface layers.
Interaction of Coal Particles Injected into Argon and Hydrogen Plasmas
Authors: Littlewood K.
Published: March 2011

Rapid heating of coal to temperatures in excess of 1500 K yields lower hydrocarbons which, if conditions are correct, will consist mainly of acetylene. Such conditions involve reaction times of 0.1 to 10 ms, together with rapid rates of quenching. Appropriate conditions have been achieved on a laboratory scale using a d.c.-arc plasma jet.
Design and use of an Efficient Plasma Jet Reactor for High Temperature Gas/Solid Reactions
Authors: Giacobbe F. W. , Schmerling D. W.
Published: March 2011

A unique and efficient plasma jet reactor has been developed and used to study the high temperature production of carbon monoxide from a reaction between powdered carbon and a pure carbon dioxide plasma. The plasma jet reactor was designed to allow the injection of powdered carbon above the arc discharge region rather than into the plasma flame below the arc discharge region. High yields of carbon monoxide, produced at relatively high efficiencies, were a direct result of this technique. The plasma jet was also designed to enable rapid changing and testing of various anode inserts

Average yields of carbon monoxide in the product gases were as high as 80–87% in selected experimental trials. Carbon monoxide was produced at rates exceeding 15,000 1/hr (at STP) with a power expenditure of 52 Kw.
In-Flight Metal Extraction in a Novel Plasma Reactor
Authors: Reid K.J. , Moore J.J. , Tylko J.K.
Published: March 2011

A new plasma reactor system based on a stable expanded conical plasma reaction zone has been used to examine the in-flight extraction of metals from mineral concentrates. The basic principles of the plasma system and details of the equipment are described. Results obtained from the treatment of taconite concentrate, low grade chromite concentrate and a copper-nickel concentrate are presented and discussed.
Plasma-Melted and Rapidly-Solidified Powders
Authors: Cheney Richard F.
Published: March 2011

A novel process is described for making rapidly solidified powders. In its simplest form, powders are melted in a high-temperature plasma and the resulting high-velocity spray is quenched into a fluid medium. Rapid cooling rates are achieved by free fall in inert gases, by quenching into liquid argon or nitrogen, or by impacting against a chilled, moving substrate. Any composition can be processed as long as it or its constituents are available in powder form. When necessary, alloy or composite components are agglomerated to 15–45μm diameter prior to plasma synthesis. The agglomeration is typically achieved by spray drying. Powders with melting points up to and including tungsten have been melted.
Melting of Powder Particles in a Low Pressure Plasma Jet
Authors: Wei D. , Apelian D. , Correa S. M. , Paliwal M.
Published: March 2011

A numerical model has been developed to predict the temperature profile of particles injected in a D.C. plasma jet. The equations governing particle melting were applied to spherical powders of binary model alloys. Thermophysical properties of the gas and the powder material have been taken to be temperature dependent. In the proposed model, the latent heat of melting was taken into account by introducing apparent enthalpy as a function of the fraction of liquid formed which can be derived from equations describing non-equilibrium melting. The temperature and velocity profiles of the plasma jet used in this analysis are for a free jet (without target interference) and were calculated using the parabolic Navier-Stokes equation with a K-E turbulence model. Correction factors have been introduced to take into account non-continuum effects encountered in the low pressure environment and the results show that both heat and momentum transfer between the plasma gas and the injected particles are reduced.
Microprocessor Control of the Spraying of Graded Coatings
Authors: Kaczmarek R. , Robert W. , Jurewicz J. , Boulos M.I. , Dallaire S.
Published: March 2011

A systematic study was made of the characteristics of a microprocessor controlled powder feeder in view of its utilization for the deposition of graded coating. The unit tested had the capability of feeding three different powders at rates which could be continuously varied up to about 40 g/min. MgOZrO2. was deposited on a stainless steel substrate using a series of thin (Ni/Cr)-Zirconia coats as intermediate layers. The results showed that such a technique could provide a valuable means of achieving a precise and effective control on the composition of the intermediate layers which can have important effects on the final quality of the deposit.
On the Allowance for the Temperature Dependence of Plasma Properties for Selection of Dimensionless Numbers to Correlate Characteristics of Electric Arcs
Authors: Vashkevich V.A. , Kravchenko S.K. , Laktyushina T.V. , Yasko O.I.
Published: March 2011

Plasma properties as a function of heat conduction are approximated by the power-law relation, for instance, σ= σo (S*/So)nσ. Then, the temperature effect on the dimensionless number is allowed for by a factor, (S*/So)γ, the value of which is estimated by equating the dominant number or the whole set of numbers to unity. Substituting this value into the generalized equation gives the form of the correlation function. A relative contribution of each number, K1, is determined from the comparison of the exponents of the dimensionless numbers with the experimental ones.
Surface Treatment of the Glass Fibers in Low Pressure Microvave Plasma
Authors: Parosa Ryszard
Published: March 2011

In the method described here, oxygen and air plasmas were generated at pressure of 1 – 10 Torr in quartz tube placed inside various kinds of microwave cavieties. Cavieties were supplied by 10 to 500 W of microwave power / f=2.45 GHz /. Processed fiber was fastly moved across the plasma region by special driving system. Experimentally the optimal process conditions, i.e. treatment time and gas pressure, were found. Moreover, a special construction of a “long” plasma reactor for industrial application of the process was worked out.
Novel Rf-Plasma System for the Synthesis of Ultrafine, Ultrapure Sic and Si3N4
Authors: Vogt Gerald J. , Hollabaugh Charles M. , Hull Donald E. , Newkirk Lawrence R. , Petrovic John J.
Published: March 2011

A novel high-temperature plasma tube has been developed that overcomes the meltdown problem of the conventional water- and gas-cooled quartz plasma tubes commonly used. The key feature of this system is the placement of heavywalled, water-cooled copper fingers inside a quartz mantle to shield the mantle from the intense radiation of the plasma. The copper fingers act as transformers to couple the plasma to the applied rf field.

This system has been used to produce ultrafine, ultrapure silicon carbide powder by reaction of silane and methane. Powder of β-SiC has been obtained with a BET surface area of >160 m2 /g and a particle size range of 10 to 20 nm as measured by TEM. Likewise, powder of silicon nitride has been synthesized by reaction of silane and ammonia in the plasma. The resulting powder is approximately 50% Si3N4 with a mixture of α- and β-polymorphic forms. Boron carbide has also been successfully synthesized from diborane and methane.
Use of Optical Emission Spectroscopy as a Diagnostic Technique for Plasma Deposition of Hydrogenated Amorphous Silicon and Carbon
Authors: Kampas F. J.
Published: March 2011

Optical emission intensities have been measured as a function of composition for silane-argon and silane-hydrogen mixtures used in the deposition of hydrogenated amorphous silicon. It was found that changes in silane fraction have a large effect on the electron concentration and energy distribution in the discharge.
Rapid Solidification by Plasma Deposition
Authors: Apelian D.
Published: March 2011

Rapid solidification processes (RSP) have been reviewed. The structural refinement one may obtain via RSP and the consolidation methods which need to be utilized have also been reviewed. The merits of low pressure plasma deposition (LPPD) or rapid solidification by plasma deposition (RSPD) as a means of combining both the atomization and consolidation steps of RSP is highlighted. The applications and challenges of RSPD are discussed.
High Concentrations of Erbium In Crystal Silicon by Thermal Or Ion-Beam-Induced Epitaxy of Erbium-Implanted Amorphous Silicon
Authors: Custer J. S. , Polman A. , Snoeks E. , van den Hoven G. N.
Published: March 2011

Solid phase epitaxy and ion-beam-induced epitaxial crystallization of Er-doped amorphous Si are used to incorporate high concentrations of Er in crystal Si. During solid phase epitaxy, substantial segregation and trapping of Er is observed, with maximum Er concentrations trapped in single crystal Si of up to 2 × 1020 /cm3. Ion-beam-induced regrowth results in very little segregation, with Er concentrations of more than 5 × 1020 /cm3 achievable. Photoluminescence from the incorporated Er is observed.
Optical Direct and Indirect Excitation of Er3+ Ions In Silicon
Authors: Majima A. , Uekusa S. , Ootake K. , Abe K. , Kumagai M.
Published: March 2011

Optical direct and indirect excitation of erbium (Er) ions in silicon substrates was performed in order to investigate the high efficiency of Er3+− related 1.54µm emission (4I13/2→4I15/2) for direct excitation that is not concerned with the indirect band gap and low quantum efficiency of a Si host. The samples were prepared by ion-implantation or thermal diffusion methods. In each sample, photoluminescence (PL) showed the peaks originating from 4I13/2→4I15/2 of Er3+ ions.

In Er thermally diffused samples, optical excitation for energy level 4I11/2 of Er3+ ions was successfully effected by photoluminescence excitation spectroscopy (PLE). The PLE spectra consisted six peaks (963. lnm, 965.Onm, 976.lnm, 978.9nm and 980.9nm) which were caused by direct excitation (4I15/2→4I11/2) of Er3+ ions. The emission directly excited is about 2 times more intense than the indirectly excited emission. The six peaks originating from the splitting of the 4I11/2 levels meant that Er3+ ions were in the sites of noncubic symmetry. The samples prepared by Er ion-implantation did not show the effect.
Effect of The Er3+ Concentration On The Luminescence of Ca1−xErxF2+x Thin Films Epitaxially Grown On Si(100)
Authors: Barriere A.S. , Raoux S. , Favennec P.N. , L'haridon H. , Moutonnet D.
Published: March 2011

Ca1−xErxF2+x thin films, with a substitution rate, x, varying from 1 to 20%, were deposited on Si(100) substrates by sublimation of high purity solid solution powders under ultra-high-vacuum. Rutherford backscattering studies have shown that the films have the composition of the initial solid solution powders, are quite homogeneous and are epitaxially grown on the substrates.

The optical properties of these films were studied by means of cathodoluminescence and photoluminescence. At room temperature, the emissions due to the de-excitations from the 4S3/2, 4F9/2, 4I11/2 and 4I13/2 excited levels to the 4I15/2 ground state of Er 3+ (4f11) ions are easily detected (λ = 0.548, 0.66, 0.98 and 1.53 µm)

The strong 1.53 µm infrared luminescence, which presents evident potential applications for optical communications, is maximum for an erbium substitution rate included between 15 and 17%. These Er concentrations are three or four orders of magnitude greater than the optimum ones in the case of Er-doped semiconductors, which are close to 1018 cm−3.In the visible range, the luminescences are also important.They allow us to detect high energy ion or electron beams. However their maximum efficiencies were observed for a relatively low erbium concentration, close to 1%. These different behaviours are explained by the cross relaxation phenomena, which depopulate the higher levels to the benefit of the 4I13/2→ 4I15/2 transition. The energy distribution of the Stark sublevels of the 4I15/2 state, which results from crystal field splitting, was deduced from a photoluminescence study at 2K. The obtained results show that the environment of the luminescent centres does not change with the erbium concentration.

At last, it must be noted that the refractive index of the layers increases with the erbium concentration, leading to the realization of optical guides. Consequently opto-electronic components could be developed from such erbium doped heterostructures.
Luminescence Study of The INTRA-4f Emissions from GaAs:(Er+O) and AlxGal1−xAs:(Er+O)
Authors: Colon Jose E. , Elsaesser David W. , Yeo Yung Kee , Hengehold Robert L. , Pomrenke Gernot S.
Published: March 2011

A systematic photoluminescence study of erbium and oxygen co-implantation into GaAs and AlxGal1−xAs with × = 0.1, 0.2, 0.3, and 0.4 was carried out. The addition of oxygen greatly enhanced the Er emission intensity from AlxGal1−xAs:Er while the O and Er co-doping into GaAs rather made the Er emission intensity decrease from that of the GaAs:Er. The Er emission intensity from AlxGal1−xAs:(Er+O) generally increases with increasing Al mole fraction and O dose up to 1 × 10 15/cm2, but it does not depend much on the substrate conductivity.
Lattice Location and Photoluminescence of Er in GaAs and Al0.5Ga0.5As
Authors: Alves E. , Da Silva M.F. , Melo A. A. , Soares J.C. , Van Den Hoven G.N. , Polman A. , Evans K.R. , Jones C.R.
Published: March 2011

Epitaxial Er-doped GaAs and Al0.5Ga0.5As films, 1.6 μm thick, grown by MBE on (100) GaAs substrates at 560°C, with Er concentrations in the range 9 × 1017 to 2 × 1020 cm−3 were studied with RBS/channeling and photoluminescence techniques. Angular scans in the <110> and <111> axial and (111) planar directions indicate that the Er atoms in GaAs are located on interstitial sites. In Al0.5Ga0.5As doped with 5 × 1019 Er cm−3, 70% of the Er atoms are on positions slightly displaced from the interstitial site, the rest presumably substitutional. In Al0.5Ga0.5As doped with 9 × 19 Er cm−3, more than 88% of the Er atoms are on substitutional sites.

Photoluminescence around 1.54 μm is observed at room-temperature in Er-doped Al0.5Ga0.5As. Both the low and highly Er-doped samples show similar luminescence intensities; the luminescence lifetimes are on the order of 1 ms. The Er-doped GaAs does not show any measurable signal at room-temperature. Correlation of the luminescence data to the Er lattice location suggests that only substitutional Er in AlGaAs is in the luminescent trivalent state.
Optical Activation of Ion Implanted Rare-Earths
Authors: Favennec P.N. , L'haridon H. , Moutonnet D. , Salvi M. , Gauneau M.
Published: March 2011

A review of the main results concerning the ion implantation of the rare-earth elements is given.

To obtain the best optical activation of rare-earths, we attempt to optimize the implantation (energy, dose) and annealing (temperature, duration) conditions. The studied materials are Si, II-VI binaries (ZnTe, CdS), III-V binaries (GaAs, InP), III-V ternaries (GaAlAs, GaInAs) and III-V quaternaries (GaInAsP).