bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoluminescence Fatigue in Laterally-Ordered (GaP)2/(InP)2 Short-Period-Superlattices (SPS) Grown by Molecular Beam Epitaxy
Authors: Liu X. C. , Gu S. Q. , Reuter E. E. , Bishop S. G. , Chen A. C. , Moy A. M. , Cheng K. Y. , Hsieh K. C. 
Published: March 2011

AbstractSpontaneously laterally ordered (GaP)2/(InP)2 short period superlattices (SPS) grown by Molecular Beam Epitaxy (MBE) on nominal (100) GaAs substrates have been studied by photoluminescence (PL) spectroscopy. The samples studied included SPS comprising 110 pairs of (GaP)2/(InP)2 (total thickness σ90 nm) and multiquantum well structures in which quantum wells comprising 12 pairs of (GaP)2/(InP)2 SPS layers (thickness σ10 nm) are alternated with lattice-matched GaInP random alloy barrier layers. The 5K PL spectra include a σ1760 meV nearband edge band, and a much broader, lower energy (σ1670 meV) luminescence band that exhibits an unusual fatiguing behavior; its intensity diminishes monotonically during continuous illumination by the exciting light. This fatigued PL state is metastable at low temperatures. In the quantum well structure, although the relative intensity of the lower energy band is significantly weaker in comparison to the higher one, the fatiguing behavior still exists. However the fatiguing rate is slower in quantum well structures than that observed in the thick SPS film.
Space Distribution of Deep Levels in SiGe/Si Heterostructure
Authors: Rong Zhang , Kai Yang , Shulin Gu , Yi Shi , Hongbin Huang , Ronghua Wang , Ping Han , Liqun Hu , Youdou Zheng , Qi Li 
Published: March 2011

AbstractThe small-pulse DLTS had been developed to measure distribution of deep levels in CVD grown SiGe/Si heterostructure before and after thermal processing at 800°C. Changes of defect states was found and after processing the original single deep level 0.62eV under the condition band split into two separated traps. A new weak deeper trap signal was found only in the just relaxed region. It could be Ge-related defect complex with misfit dislocations.
Occurrence of Ground and Excited-State Impurity Bands in Silicon Inversion Layers: Electric Field Effects
Authors: HipÓlito O. , LeÃO Salviano A. , Ferreira Da Silva A. 
Published: March 2011

AbstractWe investigate the effects of charged impurities in n-type Silicon inversion layers. We show the occurrence of ground and excited-state impurity bands as a function of electric field and concentration. Also the effects of disorder and for given impurity concentrations, the lowest excited band play an essential role in the optical and transport measurements. For high electric fields the impurity bands go to the ideally 2D separated bands.
Optical Spectroscopy of Defects in GaAs/AlGaAs Multiple Quantum Wells.
Authors: Monemar B. , Holtz P. O. , Bergman J. P. , Zhao Q.X. , Harris C.I. , Ferreira A. C. , Sundaram M. , Merz J.L. , Gossard A.C. 
Published: March 2011

AbstractThe study of electronic properties of GaAs/AlGaAs quantum wells (QWs) has traditionally been focused on intrinsic phenomena, in particular the free exciton behaviour. Defects and impurities have often been regarded as less relevant compared to the case of bulk semiconductors. Doping in QWs is important in many applications, however, and recently the knowledge about the structure of shallow donors and acceptors from optical spectroscopy has advanced to a level comparable to the situation in bulk semiconductors. A dramatic difference from the bulk case is the common occurrence of localisation effects due to interface roughness in QW structures. The recombination of bound excitons (BEs) differs drastically from bulk, BE lifetimes decrease with decreasing well thickness Lw, but increase with decreasing barrier thickness Lb (at constant Lw) below Lb=70Å. Exciton capture at impurities is a process which is strongly influenced by the localisation potentials from the interface roughness. The recombination process in doped QWs involves a nonradiative component, for shallow acceptors an excitonic Auger process has been identified. Deep nonradiative defects in the (MBE grown) QW as well as in the barrier material are manifested in measurements of the PL decay time vs temperature. In undoped multiple QWs the decay times vs T are consistent with thermal emission out of the well into the barrier, where nonradiative recombination via deep level defects occur. Nonradiative recombination in the well itself can be studied in electron-irradiated structures. Preliminary data also demonstrate the feasibility of hydrogen passivation of dopants as well as deep levels in the QW structures.
Carbon Doping of InGaAs for Device Applications
Authors: Stillman G.E. , Stockman S.A. , Colomb C.M. , Hanson A.W. , Fresina M.T. 
Published: March 2011

AbstractCarbon has gained wide acceptance as a p-type dopant for GaAs-based device structures due to its low atomic diffusivity. Carbon doping of InGaAs, however, is complicated by the amphoteric nature of C and difficulty in incorporating C efficiently during epitaxial growth. We have achieved hole concentrations as high as 7x1019 cm−3 in CC14-doped InGaAs grown at low temperature by MOCVD. Growth-related issues include the effect of CCl4 on the alloy composition due to etching during growth, and the incorporation of hydrogen, which passivates the C acceptor and reduces the hole concentration during growth and during the post-growth cool-down. The effect of H passivation on minority carrier transport has been characterized by the zero-field time-of-flight technique. High frequency InP/InGaAs HBTs with a C-doped base have been demonstrated with ft = 62 GHz and fmax = 42 GHz, which is comparable to the best performance reported for MOCVD-grown InP/InGaAs HBTs.
Dislocation Distribution in Graded Composition IngaAs Layers
Authors: Molina S.I. , Gutiérrez G. , Sacedón A. , Calleja E. , García R. 
Published: March 2011

The defect distribution of a graded composition InGaAs layer grown on GaAs by MBE has been characterized by TEM (XTEM, PVTEM, HREM). The observed configuration does not correspond completely with that theoretically predicted. Dislocation misfit segments are in a quantity much bigger than in constant composition layers. Dislocation density is quite uniform up to a certain layer thickness t1. Few dislocations are observed between this t1 thickness and a larger thickness t2. Dislocation density is below the detection limit of XTEM for thicknesses bigger than t2. Some dislocations are observed to penetrate in the GaAs substrate.Several mechanisms (reactions between 600 dislocations, Hagen-Strunk and modified Frank-Read processes) are proposed to explain the interactions of dislocations in the epilayer and their penetration in the substrate.
Raman Scattering by Lo Pronon-Plasmon Coupled Mode in Heavily Carbon Doped P-Type InGsAs
Authors: Qi Ming , Luo Jinsheng , Shirakashi Junichi , Tokumitsu Eisuke , Nozaki Shinji , Konagai Makoto , Takahashi Kiyoshi 
Published: March 2011

AbstractThe Raman scattering from LO phonon–plasmon coupled (LOPC) mode in heavily carbon doped p–type InxGa1–xAs grown by metalorganic molecular beam epitaxy (MOMBE) was studied experimentally. Only one LOPC mode appears between the GaAs–like and InAs–like LO modes was observed. The peak position of the LOPC mode is near the GaAs–like TO mode frequency, and is not sensitive to the hole concentration. The intensity of the mode increases with increasing the carrier concentration while the two LO modes decrease and become unvisible under the higher doping level. The hole concentration dependence of the linewidth and intensity of the LOPC mode is very similar to that in p–type GaAs. It was shown that the plasmon damping effect plays a dominant role in the p–type doping case.
Dipole Relaxation Current in N-Type AIxGa1-xAs
Authors: Scalvi Luis V.A. , Oliveira L. , Li M. Siu 
Published: March 2011

AbstractThermally stimulated depolarization current (TSDC) spectra are reported for AlxGa1-xAs alloys with direct and indirect bandgap for the first time. The experimental data reveal the presence of electric dipoles in both samples which are interpreted by using the negative-U DX center model. These data are fitted by a relaxation time distribution approach yielding average activation energies in close coincidence with the DX center binding energy value.
Rh: a Dopant with Mid-Gap Levels in InP and InGaAs and Superior Thermal Stability
Authors: Scheffler H. , Srocka B. , Dadgar A. , Kuttler M. , Knecht A. , Heitz R. , Bimberg D. , Hyeon J.Y. , Schumann H. 
Published: March 2011

AbstractWe investigate the influence of Rh-doping on electrical properties of InP and InGaAs. Deep level transient spectroscopy carried out on Rh-doped as well as undoped reference samples reveals a single Rh-related deep level in both semiconductors. While a Rh-related electron trap in InGaAs is situated at EC-0.38eV a Rh-related hole trap is found to exist in InP approximately 0.73 eV above the valence band edge. The internal reference rule for 3d transition metal deep levels is found to be valid for these 4d transition metal levels: their energy is constant across the InGaAs/InP heterojunction. We conclude these levels to be the single acceptor states of Rh substitutionally incorporated on cation sites.
Hydrogenation of Gallium Nitride
Authors: Brandt M. S. , Johnson N. M. , Molnar R. J. , Singh R. , Moustakas T. D. 
Published: March 2011

AbstractA comparative study of the effects of hydrogen in n-type (unintentionally and Si-doped) as well as p-type (Mg-doped) MBE-grown GaN is presented. Hydrogenation above 500°C reduces the hole concentration at room temperature in the p-type material by one order of magnitude. Three different microscopic effects of hydrogen are suggested: Passivation of deep defects and of Mg-acceptors due to formation of hydrogen-related complexes and the introduction of a hydrogenrelated donor state 100 meV below the conduction band edge.
Optical Spectroscopy of a Nitrogen-Hydrogen Complex in ZnSe
Authors: Wolk J. A. , Ager J. W. , Duxstad K. J. , Haller E. E. , Taskar N. R. , Dorman D. R. , Olego D. J. 
Published: March 2011

AbstractWe have observed two local vibrational modes related to H bonded to N acceptors in ZnSe samples grown by metal organic vapor phase epitaxy. The modes have been seen in both infrared and Raman spectroscopy. The new mode seen at 3194 cm-1 is assigned to an N-H stretching vibrational mode and the mode found at 783 cm-1 is tentatively assigned to an N-H wagging vibrational mode. Polarized Raman spectroscopy was used to determine that the symmetry of the defect complex is C3v, which implies that the H atom is in either a bonding or anti-bonding position.
Stoichiometry Related Phenomena in Low Temperature Grown GaAs
Authors: Missous M. , O'Hagan S. 
Published: March 2011

AbstractThe growth of GaAs at low temperatures (LT-GaAs) at or below 250 °C, under standard Molecular Beam Epitaxy (MBE) growth conditions, usually results in a massive incorporation of excess As in the lattice which then totally dominates the electrical and optical characteristics of the as grown material. We report on new phenomena associated with the growth of GaAs at 250 °C and we show, for the first time, data on highly electrically active doped material. By careful control of the growth conditions, namely As4/Ga flux ratios, material in which total defect concentrations of less than 1017 cm-3, well below the huge 1020 cm-3 that is normally obtained in LT-GaAs, can be achieved thereby demonstrating that high quality GaAs can in effect be grown at extremely low temperatures.
Femtosecond Probe-Probe Transmission Studies of Lt-Grown Gaas Near the Band Edge
Authors: Radousky H. B. , Bello A. F. , Erskine D. J. , Dinh L. N. , Bennahmias M. J. , Perry M. D. , Ditmire T. R. , Mariella R. P. 
Published: March 2011

AbstractWe have studied the near-edge optical response of a LT-grown GaAs sample which was deposited at 300 °C on a Si substrate, and then annealed at 600 °C. The Si was etched away to leave a 3-micron free standing GaAs film. Femtosecond transmission measurements were made using an equal pulse technique at four wavelengths between 825 and 870 nm. For each wavelength we observe both a multipicosecond relaxation time, as well as a shorter relaxation time which is less than 100 femtoseconds.
Photoluminescence Imaging of III-V Substrates and Epitaxial Heterostructures
Authors: Jantz W. , Baeumler M. , Wang Z.M. , Windscheif J. 
Published: March 2011

AbstractThe characterization of III-V compound semiconductor substrates and epitaxial layers with photoluminescence imaging is reviewed. The luminescence patterns of semi-insulating GaAs are dominantly determined by the concentration and distribution of nonradiative recombination centers, as shown by comparison with spectroscopic temperature and lifetime topography of photoexcited carriers. Wafers fabricated with various growth and annealing procedures are evaluated. Presently available informations on nonradiative centers in GaAs are summarized and discussed. The correlation of luminescence, absorption and resistivity topograms of InP substrates shows various interrelated influences of the Fe acceptor distribution. High resolution luminescence images of growth induced, strain induced and substrate induced defects in epitaxial heterostructures are obtained. The generation of relaxation dislocations in pseudomorphic layers is influenced by growth parameters, layer structures, layer doping and also by substrate properties. Nonradiative recombination center patterns replicate the arrangement of threading dislocations in the substrate.
Dominant Midgap Levels in the Compensation Mechanism in GaAs
Authors: Shiraxi H. , Tokuda Y. , Tohyama E. , Sassa K. , Toyama N. 
Published: March 2011

AbstractProperties of midgap levels in n-type GaAs crystals were studied by using trap density spectroscopy (TDS), capacitance-voltage and near infrared (NIR) absorption measurements. The TDS analysis for various n-type samples showed that the concentrations of the midgap level were from 2.0 × 1016 cm−3 to 3.4 × 1016 cm−3. However, those of EL2 in the same crystals were found to be from 1.1 × 1016 cm−3 to 1.3 × 1016 cm−3 by NIR absorption measurements at room temperature. On the other hand, in undoped semi-insulating GaAs crystals with carbon concentrations ranging from 6 × 1014 cm−3 to 2.4 × 1016 cm−3, the densities of the ionized EL2 determined by NIR absorption were only about 30 % of those of carbon acceptor determined by the localized vibrational mode absorption at room temperature. These differences suggest the presence of another midgap donor which does not give NIR absorption. The concentrations of this trap were estimated to be 0.8 to 1.6 times those of EL2 by decomposition of the TDS spectra into their components.
Band Edge Optical Absorption of Molecular Beam Epitaxial GaSb Grown on Semi-Insulating GaAs Substrate
Authors: Shah M. , Manasreh M.O. , Kaspi R. , Yen M. Y. , Philips B. A. , Skowronski M. , Shinar J. 
Published: March 2011

AbstractThe optical absorption of the band edge of GaSb layers grown on semi-insulating GaAs substrates by the molecular beam epitaxy (MBE) technique is studied as a function of temperature. A free exciton absorption peak at 0.807 eV was observed at 10 K. The free exciton line is observed in either thick samples (5μm thick) or samples with ∼0.1 μm thick AlSb buffer layers. The latter samples suggest that the AlSb buffer layer is very effective in preventing some of the dislocations from propagating into the MBE GaSb layers. The fitting of the band gap of the GaSb layers as a function of temperature gives a Debye temperature different than that of the bulk GaSb calculated from the elastic constants.
A Tem Study of Defect Structure in GaAs Film on Si Substrate
Authors: Nahm Sahn , Lee Hee-Tae , Kim Sang-Gi , Cho Kyoung-Ik 
Published: March 2011

AbstractFor the GaAs buffer layer deposited on Si substrate at 80°C and annealed at 300°C for 10 min, the size of most GaAs islands was observed as ∼ 10 nm but large islands (∼ 40 nm) were also seen. According to the calculation of spacing of moire fringes, large GaAs islands are considered to be rotated about 4 ° with respect to the Si substrate normal. However, for the main GaAs film overgrown on the GaAs buffer layer at 580 °C, moire fringes with the spacing of 5 nm (GaAs film without rotation) completely covered the surface of Si substrate. Misfit dislocations and stacking faults were already formed at the growth stage of buffer layer. Stacking faults and misfit dislocations consisting of Lomer and 60 ° dislocations were observed in GaAs films grown at 580 °C. However, after rapid thermal annealing at 900 °C for 10 sec, only Lomer dislocations with 1/2[110] and 1/2[-110] Burgers vectors were observed.
The Growth of InAsSb/InGaAs Strained-Layer Superlattices by Metal-Organic Chemical Vapor Deposition
Authors: Biefeld R. M. , Baucom K. C. , Kurtz S. R. , Follstaedt D. M. 
Published: March 2011

AbstractWe have grown InAsl-xSbx/Inl-yGayAs strained-layer superlattice (SLS) semiconductors lattice matched to InAs using a variety of conditions by metal-organic chemical vapor deposition. The V/III ratio was varied from 2.5 to 10 at a temperature of 475 °C, at pressures of 200 to 660 torr and growth rates of 3 - 5 A/s and layer thicknesses ranging from 55 to 152 Å. The composition of the InAsSb ternary can be predicted from the input gas molar flow rates using a thermodynamic model. At lower temperatures, the thermodynamic model must be modified to take account of the incomplete decomposition of arsine and trimethylantimony. Diodes have been prepared using Zn as the p-type dopant and undoped SLS as the n-type material. The diode was found to emit at 3.56 μm. These layers have been characterized by optical microscopy, SIMS, x-ray diffraction, and transmission electron diffraction. The optical properties of these SLS's were determined by infrared photoluminescence and absorption measurements.
Electron Beam Induced Degradation of 2Deg in AlGaAs/GaAs Heterostructure
Authors: Wada T. , Kanayama T. , Ichimura S. , Sugiyama Y. , Komuro M. 
Published: March 2011

AbstractThe effects of low-energy electron irradiation on the two-dimensional electron gases (2DEG's) in AlGaAs/GaAs heterostructures have been investigated. Not only the electron mobility of the 2DEG's but also the two-dimensional (2D) carriers are found to be reduced by the electron irradiation with the incident energies between 3.5 k and 8 keV and the electron dose of 1×1016 and 1×1017 /cm2. The degraded mobility and the removed carriers by the low-energy electron irradiation are shown to recover by isochronal annealing to some extent, but not completely below 400°C. It is also found that considerable amount of scatterers which are created by an electron irradiation at room temperature are also created by an irradiation at 90 K. Comparing the experimental results with the Monte Carlo simulation, we speculate that the mobility degradation and the 2D carrier compensation are partly caused by the formation of complex defects in the GaAs buffer layer which are due to the excitations of core electrons of As, and that the mobility is further degraded by the formation of short-range scatterers in the heterointerface.
D− Impurities in a Quasi-Two-Dimensional System: Statistics and Screening
Authors: Li W. J. , Wang J. L. , Cheng J.-P. , Holmes S. , Wang Y. J. , Mccombe B. D. , Schaff W. 
Published: March 2011

AbstractFar infrared spectroscopic studies of electron-density- and magnetic-field-dependenceof manyelectron effects on silicon donor impurities confined in GaAs quantum wells are presented. At low excess electron densities, transitions from D− singlet and triplet states are observed. Temperature- and polarization-dependence measurements show that the relative absorption strengths of various spectroscopic features (D0, D−, and CR) are in qualitative agreement with a statistical calculation in thermal equilibrium in high magnetic fields. At large excess electron densities, the “D−” transition energy shifts to higher energy when electron density is increased, and the magnetic-field dependence of the transition energy exhibits discontinuities in slope at integer filling factors. The spectroscopic features and their relation to excess free carriers and the role of screening and correlation are presented and discussed.
Density of States of Hydrogenic Impurities in GaAs/GaAlAs Quantum Wires
Authors: LeÃo Salviano A. , HipÓlito O. , Ferreira Da Silva A. 
Published: March 2011

AbstractWe investigate the occurrence of impurity density of states of hydrogenic impurities placed on the axis of a cylinder quantum-well wire of GaAs/GaAlAs structure. The effects of disorder are taken into account in the calculation. It is shown that for a specific radius of the wire, the peak energy of the density of states as a function of the impurity concentration increases very fast enlarging the bandwidth. The impurity bands are considered for the observed binding energy and radius as well as for the impurity concentration of experimental interest.
Single-Source Precursors to Niobium Nitride and Tantalum Nitride Films
Authors: Winter Charles H. , Jayaratne Kumudini C. , Proscia James W. 
Published: March 2011

AbstractHerein we report our efforts to prepare new precursors to niobium nitride (NbN) and tantalum nitride (TAN, Ta3N5) thin films. Treatment of MC15 (M = Nb, Ta) with tertbutylamine in benzene solvent affords complexes of the formula [MCI2 (NtBu)(NHtBu)(NH2tBu)]2. The niobium complex [NbC12(NtBu)(NHtBu)- (NH2tBu)]2 affords NbN films on glass substrates between 500-600 °C, while the tantalum analog [TaC12(NtBu)(NHtBu)(NH2tBu)]2 gives films of Ta3N5 in this temperature range. Treatment of MCI5 (M = Nb, Ta) with 1,1-dimethylhydrazine in dichloromethane solvent affords complexes of the formula [MC12(NNMe2)(NHNMe2)(NH2NMe2)]n. These hydrazido complexes afford cubic MN films upon glass substrates at ≥400°C. Analyses of the films are presented.
Manufacturing of Covalent Ceramics by Exothermic Reactions
Authors: Deevi Seetharama C. 
Published: March 2011

AbstractManufacturing of high temperature materials is an energy expensive process, and conventional techniques require long periods of homogenization to ensure uniform chemical composition in large batches of material. Several covalent ceramics, and high temperature materials can be manufactured by utilizing the exothermicity of the reactants. Some of the salient features of combustion synthesis, approaches to densify the combustion synthesized product, and other processes that utilize exothermic reactions for the synthesis of materials have been discussed.
Ceramic Coatings for PBR Components
Authors: Barletta Robert. E. , Ludewig H. , Powell J. R. , Vanier P. E. 
Published: March 2011

AbstractParticle bed reactors (PBRs) have the potential for providing compact power sources for both space power and propulsion applications. The reactors operate in the temperature range of 2000 to 3000 K and, for propulsion systems, utilize hydrogen as a coolant. Given these overall operating conditions, the need exists to develop and verify the performance of various reactor components, particularly those which must operate at the more extreme conditions of temperature and hydrogen flow rate. These components must undergo multiple thermal cycles between cryogenic and exit temperatures. In addition, some of the components are subject to a thermal gradient of thousands of degrees Kelvin over a few centimeters.A number of approaches directed towards meeting these needs have been developed. These include both monolithic ceramics (e.g. boron nitride) as well as coated composites consisting of refractory carbides (ZrC, NbC and TaC) on carbon-based substrates. Full and partial scale components have been fabricated and tested under prototypic conditions. The results of this developmental effort will be described.