bluuebunny/crossref_metadata_2025 huggingface dataset:
Special Grain Boundaries in Alumina
Authors: Morrissey K. J. , Carter C. B.
Published: March 2011

A particular type of grain morphology observed in commercial polycrystalline compacts of α-alumina is discussed along with special features which have been found to be associated with this morphology. The particular feature of interest is the occurrence of grains which are referred to in this paper as being lath-like in appearance. The important features of these lath-like grains include the occurrence of faceted grain boundaries which are often associated with pores and the special geometric relationships between the grains and the surrounding matrix.
Cathodoluminescence Emission from Crystalline Linbo3
Authors: Llopis J. , Ballesteros C. , Gonzalez R. , Chen Y.
Published: March 2011

Cathodoluminescence (CL) emission from as-grown and indented LiNbO3 single crystals has been studied. The spectrum is strongly affected by deformation of the surface region. Three emission bands at about 410, 525 and 580nm have been observed. Irradiation with the electron microscope beam at very high current intensities causes a severe damage on the irradiated area. This effect can also be observed on the indented areas where the indentation pyramid can not be recognized after prolonged irradiation.
Diffusion Mechanisms in Transition-Metal Oxides
Authors: Peterson N. L.
Published: March 2011

Results are presented for cation self-diffusioninCu2O and Cr2O3as a function of temperature and deviation from stoichiometry. A defect model for Cu2O involving neutral and singly charged copper vacancies, electron holes, and singly charged oxygen-interstitial ions is developed and fit to the tracer-diffusion data, the electrical-conductivity data, and the stoichiometry data, yielding concentrations and mobilities of these defects. The diffusion results for Cr2O3single crystals indicate that cation self-diffusion takes place by triply charged vacancies and that previous diffusion results for polycrystalline Cr2O3are dominated by grain-boundary diffusion.
Ion Implantation In Linbo3;
Authors: Wilson R. G. , Jamba D. M. , Betts D. A.
Published: March 2011

Ion implantation is used to fabricate waveguides in LiNbO3;. We have implanted a variety of ions into LiNbO3; at energies from 100 to 300 keV and have been able to profile their depth distributions by secondary ion mass spectrometry. We report here their depth distributions and range parameters determined from Pearson IV fitting.
Time Dependence of Current Injection Phenomenon in Nickel-Doped MgO Crystals at High Temperatures
Authors: Tsang K. L. , Tohver H. T. , Chen Y.
Published: March 2011

The electrical conduction mechanisms in MgO:Ni with Pt electrodes at 1473 K are studied over electric field ranges up to ∼10 kV/cm. The current transients induced by pulsed changes of the applied voltage as well as transient shortcircuit currents have been measured and analyzed to yield two electron hole recombination lifetimes of 10 and 250 s. The main features of the results are consistent with the double injection model of the electrical breakdown of MgO at high temperatures.
Physical Structure and the Electrochromic effect in Tungsten Oxide Films
Authors: Giri A. P. , Messier R.
Published: March 2011

In all previous studies of tungsten oxide films it has been implicitly assumed that the film is uniform except for grain boundaries in polycrystalline films. In this study we show that amorphous tungsten oxide thin films contain highly anisotropic void networks which not only dominate their physical structure but also control their electrochromic behaviour. The void network structure is controlled primarily through ion bombardment of the growing film during deposition while the film stoichiometry HyWO3−x is controlled by the reactive sputtering processes of tungsten in Ar/O2/H2 atmospheres. The evolutionary growth model of physical structure was studied in detail by both transmission and scanning electron microscopy. On the basis of physical structure-property correlations we are able to consistently explain the basic electrochromic characteristics and chemical stability of the films. Such information leads to better understanding of the problems and limitations inherent in thin film electrochromic devices.
Sintering of AIN Powder Compacts
Authors: Akaishi M. , Horie Y.
Published: March 2011

Pure-AINpowder compacts have been fabricated by isostatic pressing and impact forming in the pressurs range of 1.5 ˜ 5.5 GPa. The density of these compacts was in the range of 70 ˜ 90% of the theoretical. The mean particle size was reduced from 20 μm to a few micron meters depending on compaction pressures. The density changes observed aftersinteringat temperatures above 1,600°C were independent of initial starting densities. A similar shrinkage was observed when residual strains were eliminated by annealing at 1,550°C for 30 min. Micro-structures of the sintered specimens showed a mixed region of either extensive grain growth or little growth.
X-Ray Line Broadening Studies on Aluminum Nitride, Titanium Carbide and Titanium Diboride Modified by High Pressure Shock Loading
Authors: Morosin B. , Graham R. A.
Published: March 2011

Powders of AlN, TiC and TiB2 have been subjected to controlled shock loading with peak pressures in the samples between 14 to 27 GPa and preserved for post-shock study. Broadened x-ray diffraction peak profiles are analyzed by a simplified method and show increases in residual lattice strain and small decreases in crystallite size. Strain values range from 10−5 to 10−4 for TiB2 and to values larger than 10−3 for TiC and AlN.
The Design of Composite Materials For Electro-Mechanical and Electro-Thermal Applications.
Authors: Cross L. E.
Published: March 2011

In composite materials for electro-mechanical applications, the importance of the mode in which the constituent phases are interconnected (connectivity) was stressed. For the tensor properties of mechanical, piezoelectric, and dielectric behavior, controlling the manner in which fields and fluxes thread through the composite can make orders of magnitude change in the coupled properties.

Examples were drawn from piezoelectric ceramic:polymer composites for uniaxial and hydrostatic (hydrophone) pressure sensing where the 1:3 connected transversely reinforced composite can be shown to exhibit a figure of merit more than 103 that of the piezoceramic phase alone. In these systems, the importance of poisson ratio effects in the polymer phase were evident, and some new composite systems where the hydrostatic stiffness of the elastomer phases may be better exploited were considered.

In electro-thermal applications such as in pyroelectric composites, the requirements of small-size and low-thermal mass put rigorous limits upon the scale of the composite microstructure. Techniques which achieve the appropriate scaling were described and preliminary data showed strong enhancement of the secondary effects in these composites were presented.
TEM Studies of Alloy Clustering in InAlAs Strained Layers
Authors: Peiro F. , Cornet A. , Morante J. R. , Clark S. A. , Williams R. H.
Published: March 2011

Transmission electron microscopy studies have been performed to characterise InxAl1−xAS layers grown by Molecular Beam Epitaxy on (100) InP substrates. The first observations of compositional nonuniformities in strained InAlAs layers are reported. The coarse quasiperiodic structure present in each sample has been found to be dependent upon the growth parameters and the sample characteristics such as strain, thickness and x value.
Atomie Layer Epitaxy ia a Rotating Disk Reactor
Authors: Liu H. , Zawadzki P. A. , Norris P. E.
Published: March 2011

Current difficulties of Atomic Layer Epitaxy (ALE) include relatively low growth rates and narrow process windows. Gas phase reaction, complex behavior of valve switching and purging times are suggested as the major causes [1,2]. We have used a movable X-shaped mechanical barrier to divide the growth chamber into four zones. Each zone supplies either source gas or purging hydrogen. If the barrier is positioned 0.5–2 mm from the wafer carrier, it can efficiently shear off the boundary layer and therefore reduce gas phase reactions. The substrate, constantly rotating beneath the barrier, is alternately exposed to group III or V sources by purging zones. The result is that process times are significantly reduced, saturated growth rate of 1 μm/hour is obtained and a relatively wide process window is observed. It was found that the growth mode was not purely ALE, due to source gas mixing which contributes an additional, possible kinetically limited, component of growth rate. However, this was also found to result in uniform film.
Quantum Well Shape Modification in Quaternary Quantum Wells
Authors: Köteles Emil S. , Masum Choudhury A. N. M. , Levy A. , Elman B. , Melman P. , Koza M. A. , Bhat R.
Published: March 2011

Quantum well interdiffusion has been employed, for the First time in the quaternary InGaAsP/InP system (grown lattice matched to InP substrates), in order to modify the as-grown, nominally square, shapes of single quantum wells so as to increase their bandgap energies. This was accomplished, in a spatially selective manner, by using low energy ion implantation through a mask to generate vacancies. Subsequent rapid thermal annealing drove these vacancies down to the quantum wells where their presence enhanced the thermally driven interdiffusion of atoms between the well and barrier layers. The goal of this work is to develop a simple process for the integration of optoelectronic devices with differing functions.
Dependence of the Defects Present in InAlAs/InP on the Substrate Temperature
Authors: Peiro F. , Cornet A. , Herms A. , Morante J. R. , Georgakilas A. , Halkias G.
Published: March 2011

The crystalline quality of InAlAs layers, grown by Molecular Beam Epitaxy on (100) InP substrates, has been investigated by Transmission Electron Microscopy in order to study the influence of InAlAs growth temperature (Tg) on the density of structural defects present in the layers. Tg was varied from 300°C up to 530°C. The density of stacking faults and threading dislocations drops dramatically as Tg increas
Growth and Stability of Strained-Layer Multiple Quantum Wells
Authors: Niki Shigeru , Maktta Yunosuke , Yamada Akimasa , Shimada Junichi
Published: March 2011

Thirty-period In0.28Ga0.72As(100Å)/GaAs (100Å) multiple quantum wells (MQWs) have been grown by molecular beam epitaxy on (lOO)-oriented GaAs substrate with a 0.5μm-thick InyGa1-yAs (0≤y≤0.28) buffer layer interposed between the QW layer and the GaAs substrate. The MQWs with y close to the average InAs mole fraction of the QW layer exhibited good crystalline quality. It indicates that the strain is well-balanced between the GaAs and In0.28Ga0.72As layer. A significant change in their photoluminescence spectra has been observed when annealed above 750δC by means of rapid thermal annealing, implying a structural disorder in the QW“region.
Chemical Beam Epitaxial Growth of GaAs Epilayer on GaAs (100) Substrate Using Unprecracked Arsine and Trimethylgallium
Authors: Park Seong-Ju , Sim Jae-Ki , Ro Jeong-Rae , Yoo Byueng-Su , Park Kyung-Ho , Lee El-Hang
Published: March 2011

We present preliminary results aimed at investigating the effects of unprecracked arsine and trimethylgallium on the CBE (chemical beam epitaxy) growth of GaAs epilayers. We find that the growth rate rises linearly as the V/III ratio is increased when TMGa and arsine are used. All of the runs produced p-type material mainly due to carbon incorporation with the hole concentration typically of 1017 cm−3. The impurity content of the layers was found to depend distinctly on the pressure of TMGa. The significant drop in hole concentration is due in part to the hydrogen atoms generated from decomposed AsH3 which then aids in the removal of CH3 radicals on the surface. As a result of using unprecracked arsine for growth of the GaAs epilayers, we measure substantial improvements in their electrical and optical properties.
High Resolution Compound Semiconductor Mapping for Process Control
Authors: Denenberg David , Blew Austin
Published: March 2011

This paper describes the use of advanced circuitry nondestructive eddy current techniques to map compound semiconductors. Surface profiles, contour maps and diameter scans are obtained from the process wafers tested providing the necessary information to control the processes for maximum yield.

We will report on how the statistics and data analysis using sophisticated computer routines to study the radial uniformity of the compound semiconductors can be used for optimum output. Additionally, a review is presented of the basic principles of measurement and the applicable test methods and standards.

Important aspects that enable feedback to deposition and implant equipment enabling uniformity improvements are discussed. Specification improvements resulting from recent circuit and software additions and the measurement results are discussed.
Advances in Photoreflectance Analysis of HBT Wafers
Authors: Denenberg David , Blew Austin
Published: March 2011

This Poster describes the work done in a joint effort Research and Development Program with a leading University, with funding from the state, to develop a heterojunction bipolar transistor (HBT) epitaxial wafer screening tool. A computerized characteristics to HBT performance will be described.

Photoreflectance data from about twenty HBT wafers that have been grown and have had test transistors fabricated from the wafers will be analyzed to determine the bandgap of the epitaxial materials and the electric fields.

Comparison with previous works will be made in an attempt to reach a unified agreement in understanding that may lead to an ASTM test method.
Ordered Structure in GalnP/AIGalnP Quantum Wells and p-Doped Multiquantum Well AIGalnp Laser Diodes
Authors: Tanaka Toshiaki , Yanagisawa Hironori , Yano Shin-Ichiro , Minagawa Shigekazu
Published: March 2011

Zinc doping is performed on the GalnP/AIGalnP multiquantum well (MQW) structure with the aim of dissolving the ordered atomic arrangement which results in higher quantum levels and therefore shorter lasing wavelengths. It is shown that the photoluminescence (PL) peak wavelength gradually shortens with doping and decreases by 20 nm when the hole concentration reaches 1×1018 cm−3, while the PL relative intensity becomes half that of an undoped MQW layer. Therefore, a moderate level of zinc doping of around 4∼5×1017 cm−3 is desirable to shorten the PL wavelength without decreasing the crystal quality. Transmission electron nano-diffraction patterns confirm that the ordered structure in the MQW layers disappears as the hole concentration increases. On the basis of this data, uniformly p-doped and modulation p-doped MQW laser diodes are fabricated and their characteristics are compared with the undoped MQW lasers. CW operation is achieved at wavelengths of 631 to 633 nm, which is 10 nm shorter than the 643 nm in an undoped MQW laser. Comparatively low threshold currents of 73 and 88 mA are attained for uniformly p-doped and modulation p-doped MQW lasers, respectively. However, they are about 20∼30 mA higher than those of the undoped MQW lasers. This results from the large overflow of electrons from the active layer, and the fact that the differential gain becomes smaller in the 630-nm band.
Studies of Recombination Transfer in Alloys and Thin Quantum Wells of Ga0.47In0.53As/InP Using the Optically Detected Impact Ionisation Technique
Authors: OMLING P.
Published: March 2011

The possibilities of the optically detected impact ionisation (ODII) technique are demonstrated. It is shown how the ODII technique can be used to extract detailed spectroscopie information in thick InGaAs layers where resolved peaks from free excitons, bound excitons, and free-to-acceptor recombinations are obtained. In an investigation of single- and multiple-monolayer quantum wells of lattice-matched GalnAs in InP the experimental data show how the transfer of impact ionised electrons from the InP layers to the different InGaAs quantum wells, where they recombine as free excitons, can be studied. The recombination in a thicker quantum well (18 monolayer) shows a more complicated behaviour, and an explanation based on defect-related recombination, including bound-exciton and free-to-bound recombinations, is suggested.
Growth of GaAs and GaP from TMG: A Comparison
Authors: Eyers Markus , Sato Michio
Published: March 2011

In the growth of GaAs and GaP from TMG strong differences are observed. Although the shape of the Arrhenius plot of the growth rate is similar, at low deposition temperatures the GaP growth rate is lower than that of GaAs. Additionally, more carbon is incorporated into GaP than into GaAs. Mass spectrometric studies on methyl desorption show that As has a stronger ability to aid the breaking of the final Ga-carbon bond than P.
Dry Etch Self-Aligned AlInAs/InGaAs Heterojunction Bipolar Transistors
Authors: Fullowan T. R. , Pearton S. J. , Kopf R. F. , Ren F. , Chen Y. K. , Smith P. R. , Chin M. A. , Lothian J.
Published: March 2011

A dry etch fabrication technology for high-speed AlInAs/InGaAs Heterojunction Bipolar Transistors (HBT's) utilizing low-damage Electron Cyclotron Resonance (ECR) CH4/H2/Ar plasma etching is detailed. The dry etch process uses triple self-alignment of the emitter and base metals and the base mesa, minimizing the base-collector capacitance (CBC). Devices with 2 × 4 μm2 emitters demonstrated current gains of 30–50 with ft and fmax values of ≥ 80 GHz and ≥100 GHz respectively. The structure employs a two-stage collector to achieve breakdown voltage (Vceo ) of 7V. The combination of processing and layer structure delivers truly scalable high yield AlInAs/InGaAs HBT's with both DC and RF characteristics suitable for large-scale, high speed digital circuit applications.
Selective Reactive ION Etching Effects on GaAs/AlGaAs Modfets
Authors: Ballegeer D. G. , Agarwala S. , Tong M. , Ketterson A. A. , Adesida I. , Griffin J. , Spencer M.
Published: March 2011

The effects of selective reactive ion etching (SRIE) in SiCl4/SiF4 plasmas on GaAs/AlxGai-xAs heterostructures have been studied. Auger electron spectroscopy (AES) and Schottky diode measurements were performed to determine the effects of SRIE and post-SRlE processing on the surface conditions of AlGaAs layers. The degradation of the two-dimensional electron gas (2-DEG) properties of GaAs/Al0.3Ga0.7As heterostructures due to low-energy ion bombardment during SRIE were investigated by conducting Hall measurements at 300 and 77 K. Finally, measurements were performed on dry etched GaAs/Al0.3Ga0.7As modulation-doped field effect transistors (MODFETs) to determine the effects of SRIE on transconductance and threshold voltage. It is shown that extensive overetching during gate recessing results in an increase in device threshold voltages.
A Microstructual Analysis of Au/Pd/Ti Ohmic Contacts for GaAs-Based Heterojunction Bipolar Transistors (HJBTs)
Authors: Henry Bernard M. , Staton-Bevan A. E. , Sharma V. K. M. , Crouch M. A. , Gill S. S.
Published: March 2011

Au/Pd/Ti and Au/Ti/Pd ohmic structures to thin p+-GaAs layers have been investigated for use as contacts to the base region of HJBTs. The Au/Pd/Ti contact system yielded specific contact resistivities at or above 2.8 × 10−5Ω:cm2. Heat treatments up to 8 minutes at 380°C caused only limited interaction between the metallization and the semiconductor. The metal penetrated to a maximum depth of ≃2nm. Specific contact resistivity values less than 10−5Ωcm2 were achieved using the Au/Ti/Pd (400/75/75nm) scheme. The nonalloyed Au/Ti/Pd contact showed the best combination of electrical and structural properties with a contact resistivity value of 9 × 10≃6Ωcm2 and Pd penetration of the GaAs epilayer to a depth of cs30nm.
The Microstructure of ZrN/GaAs Schottky Contacts and its Correlation with Electrical Properties.
Authors: Phatak Prashant , Imaizumi Mitsuru , Weber E. R. , Newman N. , Liliental-Weber Z.
Published: March 2011

The self-aligned GaAs metal-semiconductor field-effect transistor technology requires that the gate material maintains a good rectifying contact with the GaAs substrate when subjected to high-temperature annealing around 800–900° C. ZrN Schottky contacts to GaAs were previously shown to have excellent electrical properties at high tempratures. An increase of barrier height and a decrease in the reverse breakdown voltage with rapid thermal annealing at temperatures up to 900° C has been observed. The ideality factor increases after rapid thermal annealing at 900° C.

In an attempt to explain the above observations, we investigated the interface structure of such contacts under as-deposited and annealed conditions. By high resolution TEM it was found that the interface of as-deposited samples is fairly flat but protrusions form after rapid thermal annealing treatment at 850 and 900° C. The selected area diffraction analysis shows the presence of ZrO2 near the interface.

It is therefore likely that protrusions are the cause of the degradation of electrical properties of the contacts. These protrusions may be caused by the presence of a residual oxide layer before deposition. Indeed, a deposition of ZrN after sputter cleaning the substrates before deposition procedure resulted in an abrupt interface even after annealing at 900° C.
Electrical and Optical Characterization of Pseudomorphic AlGaAs/InGaAs High Electron Mobility Transistors
Authors: Winters W. E. , Yue A. S. , Streit D.
Published: March 2011

Advances in thin-film growth techniques have allowed the succesful fabrication of transistor devices, relying on heterostructure technology to enhance their electrical performance. Devices utilizing heterostructure epitaxy have demonstrated unity current-gain cut-off frequencies well in excess of 100 GHz and maximum oscillation frequencies beyond 200 GHz.

In this paper, the AlGaAs/InGaAs pseudomorphic HEMT is studied. X-ray Double-Crystal Diffractometry and Low-Temperature Photoluminescence Spectroscopy are used to demonstrate that the InGaAs pseudomorphic layer thickness of the strained layers, did not degrade the device switching speed. This suggests that HEMT devices with higher indium contents may be permitted without having to reduce the InGaAs layer thickness due to strain accommodation requirements. Since the increase in In content lowers the electron and hole effective masses and raises the low-field mobility, higher cut-off frequencies should be possible.
DC Characteristics of Nanometer-Gatelength GaAS Mesfets
Authors: Nummila K. , Tong M. , Ketterson A. A. , Adesida I.
Published: March 2011

High-resolution electron-beam lithography has been used to fabricate GaAs MESFETs with gate-lengths ranging from 1 μm down to 30 nm. Devices were fabricated on two MESFET epitaxial layers; one with undoped GaAs-buffer layer while the other had a p- -GaAs-buffer layer. The DC characteristics including transconductance, output conductance, threshold voltage, and subthreshold current of these devices have been measured. Devices on both epitaxial layers exhibited significant short-channel effects. A negative threshold voltage shift and an increase in the subthreshold current were observed. These effects become prominent as the device aspect ratio (gate length/channel thickness) falls below 5. It is shown however that the effects were considerably suppressed in the layer with p- -GaAs buffer due to better confinement of electrons in the channel.
Reduced Mobility and PPC in In.20Ga.80As/Al.23Ga.77 as Hemt Structure
Authors: Schacham S. E. , Mena R. A. , Haugland E. J. , Alterovitz S. A.
Published: March 2011

Transport properties of a pseudomorphic In .20Ga.80As/Al.23Ga.77As HEMT structure have been measured by Hall and SdH techniques. Two samples of identical structures but different doping levels were compared. Low temperature mobility measurements as a function of concentration shows a sharp peak at a Hall concentration of 1.9.1012/cm2. This concentration coincides with the onset of second subband occupancy, indicating that the decrease in mobility is due to intersubband scattering. In spite of the low Al content (23%) large PPC was observed in the highly doped sample only, showing a direct correlation between the PPC and doping concentration of the barrier layer.
Electronic Properties of Ultrathin Isoelectronic Intralayers in Semiconductors
Authors: Mäder K. A. , Baldereschi A.
Published: March 2011

An empirical tight-binding Koster-Slater approach is used to determine the electronic properties of ultrathin“quantum wells”in semiconducting host materials of the zincblende or diamond structure. The“quantum well”is viewed as a giant two-dimensional isoelectronic impurity, and treated in a perturbational Green's function approach. We present results on the AlAs/GaAs and on the InP/InAs systems.
Growth, Behavior, and Applications of Strained InGaAs/GaAs Multiple Quantum well Based Asymmetric Fabry-Perot Reflection Modulators
Authors: Hu Kezhong , Chen Li , Madhukar A. , Chen P. , Xie Q. , Rajkumar K. C. , Kaviani K.
Published: March 2011

We report the realization of all-optical photonic switches using strained InGaAs/GaAs multiple quantum well based inverted cavity asymmetric Fabry-Perot reflection modulators monolithically integrated with GaAs/AlGaAs based heterojunction phototransistors. The photonic switches show both bistable and non-bistable switching behavior with a contrast ratio of 12:1 and optical gain of 2 to 4 dB. The design and growth considerations for such an integrated structure are also discussed.
Energy and Depth Distributions of Interface States and bulk Traps and their Electronic Effects in GalnAs/GaAs Heterojuntions
Authors: Huang Z. C. , Wie C. R. , Johnstone D. , Stutz C. E. , Evans K. R.
Published: March 2011

We have studied the lattice-mismatch-induced defects both at the interface and in the bulk (GaAs buffer layer ) of Ga0.92In0.08As/GaAs heterojunctions by means of C-V characteristics and constant capacitance deep level transient spectroscopy (CC-DLTS). The Ga0.92In0.08As (n+)/GaAs (P) samples, with the thickness of GalnAs layer at 0.1μm, 0.25μm, 0.5μm, and 1.0μm, were grown by MBE. The depth profiles of bulk hole traps in the GaAs buffer layer were measured by the DLTS technique as a function of the in-plane lattice mismatch. The concentration of lattice-mismatch-induced traps decreased exponentially with distance away from the interface. The depth distributions of the mismatch-induced bulk traps appeared to be affected by the pre-existing bulk traps and the dopant impurities in the GaAs buffer layer. Energy distribution of the interface states was obtained by the CC-DLTS and C-V measurements independently. All heterojunctions showed a minimum in the interface state density at about EV+0.83eV. The U-shaped energy distribution with donor- and acceptor-like states is interpreted by the disorder-induced-gap-states model.
Bonding of Hydrogen Implanted at 80K INTO III-V Semiconductors
Authors: Stein H. J.
Published: March 2011

Hydrogen implantation at 80K is shown to introduce As-H centers in GaAs and InAs, and P-H centers in InP. These As (P)-H centers anneal between 150 and 300K. By analogy to suggested defect assignments in electron-irradiated GaAs, it is suggested that the sites for the As (P)-H centers are metastable defects such as close vacancy-interstitial pairs. In contrast to GaAs, where absorption by Ga-H centers increases upon loss of As-H, no absorption attributable to In-H was observed in either InAs or InP. Hydrogen in an As vacancy is the suggested model for Ga-H centers. If such vacancies are thermally unstable in In-based compounds, it would explain an absence of In-H bonds and may reduce the capability for ion implantation to produce electrical isolation in In-based compound semiconductors.
Hydrogen Passivation of Si and Be Dopants in InAlAs
Authors: Roos G. , Johnson N. M. , Pao Y. C. , Harris J. S. , Herring C.y
Published: March 2011

Hydrogen passivation and thermal reactivation of Si donors and Be acceptors were investigated in In0.52Al0.48As grown by molecular beam epitaxy. The semiconducting alloy was passivated by exposure to monatomic hydrogen or deuterium from a remote microwave plasma. The passivation was achieved by exposing the samples to monatomic hydrogen at temperatures between 200 and 250 °C for 1h. The electrical activity of the dopants was monitored by spreading resistance and C-V measurements. The samples were homogeneously doped to concentrations of 1.5×1016 or 6×1017 Si / cm3 and 6×1017 Be / cm3. Both dopants were passivated by more than two orders of magnitude through the epitaxial layers. An additional annealing step (440°C, 5 min) resulted in a complete reactivation of the passivated dopants. In addition to the electrical measurements, secondary ion mass spectroscopy showed that for both the Be- and the Si-doped layers the hydrogen profiles were essentially identical to the dopant profiles throughout the epilayers. This behaviour suggests that hydrogen migration is a dopant-trapping-limited process in n-and p-type In0.52Al0.48As.
Raman Microprobe Spectroscopy and Photon Scanning Tunneling Spectroscopy: Applications to Optical Waveguides
Authors: Jackson Howard E.
Published: March 2011

Recent results from our laboratory on the characterization of optical waveguides are reviewed. In particular, two means of experimental characterization that provide spatially local information are presented. Raman microprobe spectroscopy is used to explore the role of stress in a GaAlAs channel waveguide and to characterize the nature of impurity induced compositional mixing in a multiple quantum well structure suitable for optical waveguiding. Finally, photon tunneling microscopy is shown to probe the optical waveguide evanescent field and thus the local surface and index variations in an optical waveguide.
Trimethylamine Alane for Low-Pressure Movpe Growth of AlGaAs-Based Materials and Device Structures
Authors: Schneider R. P. , Bryan R. P. , Jones E. D. , Biefeld R. M. , Olbright G. R.
Published: March 2011

The use of trimethylamine alane (TMAAl) as an alternative to trimethylaluminum (TMAl) for low-pressure metalorganic vapor-phase epitaxy (MOVPE) of AlGaAs thin films as well as complex optoelectronic device structures has been studied in detail. AlGaAs layers were grown in a horizontal reaction chamber at 20–110 mbar with growth temperatures in the range 650°C≤TG≤750°C. Wafer thickness uniformity is strongly dependent on growth pressure, and is acceptable only for the highest linear flow velocities. The 12K photoluminescence (PL) spectra of AlGaAs layers grown using TMAAl and TEGa exhibit uniformly intense and narrow bound-exciton emission throughout the growth temperature range investigated. To assess the viability of this new source for the low-pressure OMVPE growth of advanced optoelectronic devices, several optically-pumped vertical-cavity surface-emitting laser (VCSEL) structures were grown using TMAAl extensively. Room temperature lasing at 850 nm was reproducibly obtained from the VCSEL structures, with a threshold pumping power comparable to similar structures grown by molecular beam epitaxy in our laboratories.
Zinc Diffusion Rates and Profiles in AlGaAs Alloys
Authors: Smith F. T. J.
Published: March 2011

The diffusion rate of Zn in AlxGa1−xAs alloys has been determined, for values of x up to 1.0, as a function of temperature. At 625°C the diffusion coefficient shows a strong dependence on x, reaching a maximum at about 65% Al. A similar rapid increase in diffusion coefficient with x is seen at 700°C. The zinc concentration profiles are similar for all values of x, showing a very abrupt diffusion front. The activation energy for diffusion decreases with increasing x.
Shubnikov-De Haas Studies of Negative Persistent Photoconductivity in AlGaSb/InAs/AlGaSb Quantum Wells
Authors: Lo Ikai , Mitchel W. C. , Manasreh M. O. , Stutz C. E. , Evans K. R.
Published: March 2011

We have measured the Shubnikov-de Haas (SdH) effect in the MBE grown Al0.6Ga0.4Sb/InAs/Al0.6Ga0.4Sh single quantum well (QW) for the magnetic fields up to 4.5T and the temperatures from 1.1 K to 4.2K. The carrier concentration of the two dimensional electron gas (2DEG) was varied via the negative persistent photoconductivity (NPPC) effect. By illuminating the sample with a red light-emitting diode (LED) at the low temperature, the carrier concentration of the 2DEG in the InAs well was reduced from 5.8×1011 cm−2 to 3.6×1011 cm−2 and the corresponding quantum lifetime increased from 0.16ps to 0.21ps. The effective mass was determined by the temperature dependence of SdH oscillations and equal to (0.0317 ± 0.0005)m0.
Ion Implantation Related Defects in GaAs
Authors: Jones K. S. , Bollong M. , Haynes T. E. , Deal M. D. , Allen E. L. , Robinson H. G.
Published: March 2011

Extended defect formation is studied in ion implanted GaAs. A number of different species including Si+, Al+, Mg+, Ge+, As+, and Sn* have been investigated. Cross-sectional TEM studies have been done comparing the as-implanted structure (amorphous or crystalline) with the final defect location and morphology. The defects are identified by the same classification scheme used for implanted and annealed silicon. It is found that the threshold dose for type I defect formation is very sensitive to the implant energy for heavier ion masses. Type II, III and IV defects are unstable at annealing temperatures below 900°C. Type V defects are of a loop morphology for Si* and Ge* implants. The source of the interstitials may be a kickout process as the implanted species moves onto substitutional sites. Type V defects for Sn implants appear as precipitates which at the annealing temperature appear to be migrating in the liquid phase. Upon cooling the Sn precipitates, in many cases, solidify as grey (α) Sn.
Indium-Carbon Co-Implantation in GaAs
Authors: Madok J. H. , Haegel N. M.
Published: March 2011

We report on the formation of p+ layers in GaAs by the co-implantation of indium with carbon. Sheet hole concentrations of 2E14 cm−2 were achieved. The co-implant acts to create stoichiometric disturbances and to increase VAs concentration, allowing the C to occupy the vacant As lattice sites. The effect of In on the stoichiometry of the implanted layer was investigated. It was found that addition of 0.1–1% of a group III ion had the effect of shifting the effective As fraction toward the Ga-rich region, thus altering the crystal stoichiometry.
Impurity Profiles in InP from Ion Implantation at Elevated Temperatures
Authors: Kringhoj P. , Svensson B. G.
Published: March 2011

The chemical profiles of Zn, Ge, and Se implanted into InP at elevated temperatures have been measured with secondary ion mass spectrometry and correlated to the implantation damage as deduced from RBS/channeling measurements. An asymmetric broadening of the chemical profiles towards the bulk was found for implantation temperatures above 150°C. This effect is concluded to be due to impurity channeling during implantation.
Deep Donor and Acceptor Levels Induced by High Temperature and long time Annealing in LEC Gallium Arsenide
Authors: Marrakchi G. , Kalboussi A. , Guillot G. , Ben Salem M. , Maaref H. , Molva E.
Published: March 2011

The effects of high temperature isothermal annealing on the electrical properties of donor and acceptor defects in n-type LEC GaAs are investigated. The annealing experiments are performed under As-rich atmosphere at 1000°C for 1–4 and 16 hours followed by a very quick quenching into cold water of the quartz ampoules containing the samples. The donor and acceptor levels are detected respectively by standard (DLTS) and optical (ODLTS) deep level spectroscopy. DLTS results show the presence of one single donor level present in unannealed and annealed samples at Ec - 0.79eV which is identified as the well known electron trap EL2 Only the sample annealed for 16 hs exhibits the presence of a new electron trap named TAI at Ec - 0.32eV. The appearance of TAI is correlated in one hand with the evolution of EL2 concentration and in the other hand to the effect of long duration (16 hs) of the treatment. For acceptor levels, two hole traps HT1 and HT2 are detected respectively at EV + 0.18 eV and EV+ 0.28 eV. HT1 is detected only in samples annealed for 4 and 16 hs and HT2 is detected in all studied samples. Photoluminescence (PL) measurements show the presence of the 1.44 eV band corresponding to gallium antisite GaAs defect. This band observed in unannealed and annealed samples shows that GaAs remains stable even after thermal annealing at lOOO°C for 16 hs and it is correlated with the presence of HT2.
Oxygen in Gallium Arsenide
Authors: Alt Hans Ch.
Published: March 2011

The influence of oxygen-related defects on the compensation behavior of semi-insulating gallium arsenide has been studied. Off-center substitutional oxygen (Ga-O-Ga center) forms an electrically active defect with two levels in the fundamental gap. The negative-U ordering of these levels is the origin for very unusual electrical and optical properties. By oxygen implantation and annealing high concentrations of this center are created which are technologically useful to obtain high-resistivity surface layers.
Shallow Ion Implantation in Gallium Arsenide Mesfet Technology
Authors: de Souza J. P. , Sadana D. K.
Published: March 2011

This review emphasizes controlled shallow doping of GaAs by ion implantation for state-of-art GaAs IC technology. Electrical activation behavior of Si+ and SiF+ implanted GaAs after RTA under capless and PECVD Si3N4-capped conditions will be compared. It will be demonstrated that a remarkable improvement (> 20 %) both in carrier activation and as well mobility can be achieved by co-implanting low doses (< 1013 cm−2 of Al+ into n-dopant (including Si, Se and Te) implanted GaAs and subsequently annealing the material under capless RTA conditions. The maximum improvement in the electrical results with Al+ co-implants occurs for doses (e.g. < 1013 cm−2 for 30 keV Si+) which are used for fabricating shallow channels for submicron GaAs MESFETs. Complex dopant-annealing environment interactions during a buried p layer formation (using either Mg+ or Be+) will be discussed.
Interface Recombination in III/V Heterostructures Investigated Through the Power Dependence of Excitonic Photoluminescence
Authors: MüLlenborn M. , Haegel N. M.
Published: March 2011

Photoluminescence spectra of AlGaAs/GaAs heterostructures with layer thicknesses in the micrometer range show excitonic recombination peaks from the AlGaAs as well as the GaAs layer. Luminescence in the buried GaAs layer may be produced by charge carrier diffusion across the interface and/or photon recycling. We have monitored the luminescence intensity from both layers as a function of laser power in order to determine the dominant generation process in the GaAs layer. The ambi polar diffusion equation has been solved to derive the charge carrier distribution. Based on these data the relative intensities of the AlGaAs and the GaAs excitonic luminescence can be used to obtain information about the interface recombination in a nondestructive way. This characterization method has been applied to investigate the quality of GaAsP/GaAs interfaces as a function of increasing lattice mismatch and dislocation density.
Surface Acoustic Wave Detection of Large Lattice Relaxation of Metastable EL2 in LT-GaAs
Authors: Khachaturyan Ken , Weber Eicke R. , White Richard M.
Published: March 2011

For the first time, surface acoustic waves (SAWs) were used to study the lattice relaxation of metastable defects. A persistent increase of as much as 0.4% of the SAW velocity at low temperatures was observed after illumination of LT-GaAs; this increase could be quenched by annealing at 120–130°K. This behaviour is caused by the metastable transition of EL2-like AsGa defects and constitutes the direct experimental proof of the illumination induced large lattice relaxation of this defect.
Surface Ordering of MBE Grown 001 Ga1−xAlxAs- A Theoretical Study
Authors: Trivedi Rita , Venkatasubramanian R.
Published: March 2011

The kinetics of MBE growth of Ga1-x.,Alx,As is studied theoretically using the stochastic model of MBE growth based on the master equation approach and the random distribution approximation. The surface ordering phenomenon during the 001 growth of Ga0.5Al0.5 As is investigated as a function of the growth conditions. The atom pair interaction energy parameters for various surface configurations were obtained from the first principle calculations. The other model parameters needed in the description of the kinetic processes are obtained from the available experimental data. The ordering kinetics is studied as a function of fluxes, flux ratio and growth temperature. The degree of ordering is estimated in terms of the short range order parameter. The short range order parameter increases with temperature till 650°K and 750°K for cation to anion flux ratios 2 : 1 and 1 : 5, respectively. Beyond this critical temperature, the short range order parameter decreases. This critical temperature is identified as the kinetic order-disorder temperature. The order-disorder phenomenon observed in this theoretical study is explained in terms of the dependence of the surface migration rate of the cations on the growth temperature. The dependence on the order-disorder temperature on the flux ratio is attributed to decreased surface migration for larger flux ratios.
Electronic and Optoelectronic Applications of Materials Grown at a Low Temperature by MBE
Authors: Mishra U. K. , Kolbas R. M.
Published: March 2011

Materials grown at a low temperature by MBE and subsequently annealed at a high temperature have an excess amount of Arsenic and have demonstrated high dielectric breakdown strength and low carrier lifetime. These properties have found applications in analog and switching power applications, in picosecond pulse generation, in device isolation and in the selective intermixing of heterostructures. This paper reviews these applications.
Ultrafast Properties and Applications of GaAs and InP Based Materials Grown by MBE at Low Temperatures
Authors: Gupta S. , Mourou G. , Smith F. W. , Calawa A. R.
Published: March 2011

The ultrafast carrier dynamics in GaAs, In0.52Al0 48As on InP, and In0.53Ga0.47As on InP, grown by molecular-beam-epitaxy (MBE) at low substrate temperatures, are investigated. A reduction in the carrier lifetime is observed with decreasing growth temperatures. The shortest carrier lifetimes of typically a picosecond (ps) are obtained at the lowest growth temperature range of 150 – 200 'C. Femtosecond optical absorption and reflectance measurements have been used to verify the sub-picosecond carrier lifetimes. Photoconductive switching measurements on these materials, measured using the technique of electro-optic sampling have further confirmed the sub-picosecond carrier lifetimes, and have also resulted in the generation of subpicosecond electrical signals. These short electrical pulses have been used for a variety of ultrafast optoelectronic applications.
Characterization of Electrical Properties of Low Temperature GaAs
Authors: Wu Bin , Verma Ashish , Gamelin John , Sohn Hyunchul , Wang Shyh
Published: March 2011

LT GaAs(220°C) was grown on an n+ substrate and capped with n+ GaAs grown at 600°C (n-i-n). Complete IV and CV measurements were performed. The IV characteristics exhibit ohmic, trap-filling and space-charge-limited regimes. We have developed a model based upon the compensation of background shallow acceptors by deep donor traps, large concentrations of which have been shown to exist in LT GaAs. Computer simulation of the IV curve is compared with experimental results. The “breakdown” is attributed to trapfilling under electron injection. It is also found that when the voltage across the structure is changed, the current takes several seconds to reach steady state. This is consistent with our model, which assumes slow trapping and detrapping in the LT GaAs. High frequency CV measurements show the capacitance to be fairly constant for voltages below “breakdown”.
Study of Deep Levels in LT-GaAs Materials and SI-GaAs Wafers by an Improved Thermoelectric Effect Spectroscopy
Authors: Huang Z. C. , Wie C. R.
Published: March 2011

We have developed a simpler and more reliable method of thermoelectric effect spectroscopy (TEES) by eliminating the second heater in the technique. We have applied this method to the deep level studies in semi-insulating(SI) GaAs epitaxial layers grown at a low temperature by molecular beam epitaxy (LT-GaAs) and SI-undoped GaAs, Cr-doped GaAs. We have found that the electrical contacts on front and back surfaces of the sample are more reliable for the TEES measurement than both contacts made on the same surface. In this contact arrangement, the temperature difference of about 1–2K between the back and front surfaces was enough to produce a clear and reliable TEES data, without the need for a second heater. The results obtained by TEES are consistent with the results obtained by photo-induced current transient spectroscopy (PICTS) and by thermally stimulated current (TSC) measurements. The TEES results clearly distinguish between the electron traps and the hole traps. We will discuss the results on the various semi-insulating GaAs samples and the advantages and limitations of the TEES technique.
The Modification of the Abrasion Resistance of Type IIa (110) Diamond Using Carbon and Nitrogen Implantation
Authors: Anderson Gregory C. , Prawer Steven , Johnston Peter N.
Published: March 2011

The modification of the wear properties of type Ha diamond following ion implantation with 100 keV carbon and nitrogen has been studied at implantation temperatures of 150 and 470 K. Abrasion testing using low load multiple pass scratch testing with a Rockwell diamond indenter has shown a decrease in wear resistance. Microstructural modifications resulting from ion implantation have been assessed using Channeling Rutherford Backscattering Spectroscopy (C-RBS). No correlation was found between the presence of ion beam induced point defects (as measured by C-RBS) and the increase in wear. There are no obvious wear rate differences observed for nitrogen or carbon implantation.
The Mbe Growth of Widegap II-VI Injection Lasers and LEDs
Authors: Xie W. , Grillo D.C. , Kobayashi M. , Gunshor R. L. , Jeon H. , Ding J. , Nurmikko A. V. , Hua G. C. , Otsuka N.
Published: March 2011

Striking progress in the development of II-VI semiconductor heterostructures, coupled with seminal advances in doping, has very recently led to the first demonstration of blue and blue/green diode lasers operating from cryogenic to room temperature. The active region in these devices was based on the (Zn, Cd)Se/ZnSe multiple quantum wells (MQW) which had earlier been actively studied as a candidate for laser medium by optical pumping techniques. We report on the performance of such MQW diode lasers with emphasis on structural versatility in terms of preparation on both p-type and n-type GaAs substrates, and where sulfur is or is not incorporated for blue/green color lasing. In this work we have obtained pulsed, high power, high quantum efficiency laser emission up to near room temperature conditions. Efficient LED devices are described which operate in the blue (494nm) at room temperature.
Alloy Dependent Properties of Excitons and Deep Acceptors in CdZnTe Volume Crystals
Authors: Meyer B. K. , Hofmann D. M. , Oettinger K. , Stadler W. , Efros Al. L. , Salk M. , Benz K. W.
Published: March 2011

Cd1-xZnxTe ZriTe crystals grown by the travelling heater methode (THM) have been investigated by low temperature photoluminescence (PL). The excitonic energy gap as a function of the alloy composition was determined for the complete range of x - 0 to x - 1. The composition dependent broadening of the neutral acceptor bound exciton (A°X) line was measured and compared to theoretical calculations. The Donor - Acceptor pair luminescence in the crystals is a superposition of recombinations due to residual Cu acceptors and A - centers (anion vacancy - donor pairs ).