A photoluminescence study of defects in non-stoichiometric gallium arsenide using concurrent electrical and structural characterization

Photoluminescence has been used to identify centres associated with point defects and impurities in single crystal gallium arsenide, and this has been correlated with electrical and structural characterization of the same samples. Five different types of defect centre have been identified by this technique in material grown under different conditions of stoichiometry. These studies show systematic differences between the photoluminescence data obtained from stoichiometric and non-stoichiometric gallium arsenide. Precision lattice parameter and density measurements on the same gallium arsenide specimens indicate a deviation from stoichiometry on the arsenic-rich side of the gallium arsenide phase and it is suggested that defects primarily responsible for this stoichiometric deviation are arsenic interstitials in concentrations up to 3×10¹⁸ cm^?3. Photoluminescence measurements associate these defects in arsenic-rich gallium arsenide with an energy level of 0.036 eV.     

砷化镓晶体力学特性的各向异性计算

砷化镓因其良好的光电特性被广泛应用于电子与半导体领域, 为推动砷化镓解理加工技术, 对砷化镓材料力学特性的各向异性进行计算并分析。本研究对砷化镓各个晶面之间的夹角、面间距、原子的密度等结构参数进行计算, 基于广义胡克定律结合压痕实验, 分析砷化镓材料表层弹性模量、泊松比、剪切模量、硬度、断裂韧性等力学特性在{100}晶面沿不同晶向力学性能的变化规律。结果表明: 砷化镓不同晶面间结构参数的不同是导致砷化镓力学特性呈现各向异性的主要原因; 砷化镓在{100}晶面上弹性模量、泊松比、剪切模量的各向异性均呈现出周期性变化, 且{100}晶面的剪切模量为恒值59.4 GPa; 砷化镓{100}晶面硬度的各向异性变化幅度较小, 断裂韧性变化幅度较大, 最小值为0.304 MPa·m^1/2, 位于<110>晶向, 确定<110>晶向是裂纹最容易扩展的晶向。     

Radiation damage in solar cells

A review is given of the various aspects of solar-cell degradation in space. By way of introduction, defect creation in a solid by energetic particles is outlined, and the basic results of solar-cell theory are presented. The identification of the minority-carrier lifetime as the principal quantity of concern in solar-cell degradation then paves the way for the discussion of specific materials. The radiation damage in silicon, gallium arsenide and indium phosphide solar cells is discussed in some detail, paying particular attention to microscopic defects and their interaction with impurities.     

Acoustostimulated change in the optical absorption coefficient of gallium arsenide in the 0.81–1.77 μm wavelength range

The effect of ultrasonic waves on the spectral absorption coefficient of gallium arsenide (GaAs) in the 0.81–1.77 μm wavelength range. The treatment of GaAs single crystals with ultrasonic waves leads to a change in their coefficients of absorption of electromagnetic radiation. This phenomenon is related to the fact that an acoustic wave, being an energy carrier, modified a defect system of the crystal and produces a redistribution of impurities in the crystal lattice. The interaction of photons with acoustogenerated defects changes the optical absorption coefficient near the edge of the fundamental absorption band of GaAs.     

Mass spectrometric studies of impurities in gallium arsenide crystals

Techniques for the investigation of impurities in gallium arsenide crystals using mass spectrometry are described. The results obtained show a fair correlation with electrical measurements. Flat-bottomed etch pits are found which can be correlated with the oxygen content.The use of silica, boron nitride, alumina, and vitreous carbon crucibles is shown to contaminate the crystals. For crystals grown from silica crucibles, the silicon content decreases rapidly with increasing arsenic pressure during growth. From the distribution of impurities along the lengths of crystals, a number of distribution coefficients have been estimated.     

Hydrogen in semiconductors

Hydrogen in crystalline semiconductors has become a recent curiosity because of its high diffusivity and strong chemical activity in such materials. In contrast to the proton motion in ionic materials which gives rise to an enhanced conductivity, hydrogen in electronic materials interact with structural disorders and chemical impurities to control the electronic flow. Deep gap states in crystalline semiconductors due to various disorders such as surface/interface, grain boundaries, dislocations, irradiation and implantation damage etc. have been removed due to hydrogen bondings. Hydrogen incorporation is done by plasma and direct ion beam hydrogenation methods, implantation technique and by a novel technique of damage free introduction. The most studied materials are silicon and gallium arsenide.I - V,C - V, DLTS and IR studies have been carried out on hydrogenated semiconductors to characterize the electronic flow, gap states and the nature of chemical bonds. Improvement in ideality factors of diodes, reduction in free carrier concentration, removal or reduction of deep states and appearance of new bondings such as Si-H, P-H, B-H etc. have been observed from various techniques. The present paper reviews the various features of hydrogenation studies in crystalline silicon and gallium arsenide and highlights our results of hydrogenation studies on Pd/semiconductor devices.     

Transient electron transport in the III–V compound semiconductors gallium arsenide and gallium nitride

A three-valley Monte Carlo simulation approach is used for a detailed comparative analysis of the transient electron transport that occurs within bulk zinc blende gallium arsenide and bulk wurtzite gallium nitride. We find that in both cases that the electron drift velocity and the average electron energy field-dependent “settling times” are strongly correlated, and that the electric field resulting in the shortest electron transit-time is a function of the channel length. The calculated dependence of the peak transient electron drift velocity on the applied electric field can be used for the design optimization of short-channel high-frequency devices.     

A study of non-stoichiometry in gallium arsenide by precision lattice parameter measurements

An automatic method of precision lattice parameter measurement, capable of repeated measurement at intervals across single crystals with an accuracy of better than one part in 10⁶, has been applied to gallium arsenide. The technique has been used to compare homogeneity of material grown from the melt with that prepared by vapour and liquid epitaxy, to study material grown from the melt under various pressures of arsenic, and to investigate the effect of heavy doping on the lattice parameter. The technique is shown to provide new and interesting information on defects in gallium arsenide.     

Direct detection of electron spins and doping effects in spin-polarized electron transport in gallium arsenide

The spin Hall effect allows the direct detection of spins in semiconductors. In this study, electron spins in n-doped gallium arsenide are detected and the effects of n-type doping in gallium arsenide under drift are studied. It is found that the effects in the spin-polarized electron transport increase with increasing doping density in the moderate range, indicating that the introduction of n-type dopants increases the electron-spin lifetimes in gallium arsenide. However, the transport drifting by a high field shows no effects because of destroying the electron-spin polarization in n-doped gallium arsenide. The results are discussed in details.     

A study on the photoconductivity of a set of horizontal Bridgman semi-insulating GaAs ingots

We report in this paper a study of the photoconductivity of a set of Horizontal Bridgman semi-insulating GaAs samples. In order to obtain steady-state photoconductivity spectra, we measure the photocurrent by a procedure that consists in thermally erasing the typical GaAs photomemory. The thermal evolution, between 80 and 300 K, of the photoconductivity is also obtained. The data so obtained allow us to distinguish clearly a diversity of behaviours between the photoelectronic properties of the different samples, which could not be observed with the conventional photoconductivity technique. The way in which chromium and oxygen impurities are introduced in GaAs, as well as their charge states, seem to be strongly influenced by native defects and background impurities, which play an important role in the compensation mechanism.     

Damage in gallium arsenide crystals produced by ion implantation,abrasion and ball-milling

Gallium arsenide single crystals implanted with tellurium and cadmium ions at 50 and 150 keV at room temperature were examined using RHEED. Damage depth profiles were measured. Annealing was carried out to investigate the effect of temperature on the implantation damage. These effects which proved to be very complicated, included decomposition of the gallium arsenide, formation of beta gallium oxide and gallium telluride, and preferred orientation of the gallium arsenide. Comparisons were made with the annealing behaviour of ball-milled gallium arsenide using X-ray diffraction line broadening. The effects of various types of mechanical damage associated with specimen polishing of the gallium arsenide single crystals were also investigated.     

Solid-state gallium NMR characterization of cubic gallium nitride prepared by the reaction of gallium arsenide with ammonia

The reaction of cubic gallium arsenide (GaAs) with ammonia yielded gallium nitride (GaN). Powder X-ray diffraction patterns of the GaN products showed that they are a mixture of c- and w-GaN, while their Ga MAS NMR spectra revealed that they have the other phase of GaN besides c- and w-GaN and the high reaction temperature (≥900 °C) induces nitrogen deficiency in GaN. The peaks at 353 and 347 ppm in the ⁷¹Ga MAS NMR spectra were tentatively assigned to c-GaN and an intermediate of w- and c-GaN in the stacking order, respectively. The observed ⁷¹Ga chemical shifts of GaN, GaP, GaAs and GaSb in cubic phase were well correlated with the reciprocal of their band gaps.     

Mechanical stresses in the heterosystem germanium- gallium arsenide

Mechanical stresses in thin germanium epitaxial layers deposited by vacuum deposition on monocrystalline gallium arsenide substrates have been examined. The stresses arising are attributed to two factors: the pseudomorphic character of the growth mechanism and the gradient of structural defects in the transition layer. The experimental stress dependence has been shown to be in good agreement with the theory of the dynamic properties of dislocations.     

Steady-state and transient electron transport within the wide energy gap compound semiconductors gallium nitride and zinc oxide: an updated and critical review

The wide energy gap compound semiconductors, gallium nitride and zinc oxide, are widely recognized as promising materials for novel electronic and optoelectronic device applications. As informed device design requires a firm grasp of the material properties of the underlying electronic materials, the electron transport that occurs within these wide energy gap compound semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving field, in this paper we review analyzes of the electron transport within the wide energy gap compound semiconductors, gallium nitride and zinc oxide. In particular, we discuss the evolution of the field, compare and contrast results determined by different researchers, and survey the current literature. In order to narrow the scope of this review, we will primarily focus on the electron transport within bulk wurtzite gallium nitride, zinc-blende gallium nitride, and wurtzite zinc oxide. The electron transport that occurs within bulk zinc-blende gallium arsenide will also be considered, albeit primarily for bench-marking purposes. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art wide energy gap compound semiconductor orthodoxy. A brief tutorial on the Monte Carlo electron transport simulation approach, this approach being used to generate the results presented herein, will also be featured. Steady-state and transient electron transport results are presented. We conclude our discussion by presenting some recent developments on the electron transport within these materials. The wurtzite gallium nitride and zinc-blende gallium arsenide results, being presented in a previous review article of ours (O’Leary et al. in J Mater Sci Mater Electron 17:87, 2006), are also presented herein for the sake of completeness.     

Pressure-Dependent Behavior of Defect-Modulated Band Structure in Boron Arsenide

The recent observation of unusually high thermal conductivity exceeding 1000 W m⁻¹ K⁻¹ in single-crystal boron arsenide (BAs) has led to interest in the potential application of this semiconductor for thermal management. Although both the electron/hole high mobilities have been calculated for BAs, there is a lack of experimental investigation of its electronic properties. Here, a photoluminescence (PL) measurement of single-crystal BAs at different temperatures and pressures is reported. The measurements reveal an indirect bandgap and two donor–acceptor pair (DAP) recombination transitions. Based on first-principles calculations and time-of-flight secondary-ion mass spectrometry results, the two DAP transitions are confirmed to originate from Si and C impurities occupying shallow energy levels in the bandgap. High-pressure PL spectra show that the donor level with respect to the conduction band minimum shrinks with increasing pressure, which affects the release of free carriers from defect states. These findings suggest the possibility of strain engineering of the transport properties of BAs for application in electronic devices.     

Finite-Element Analysis of Lossy TE-TM modes in Metal-Clad Optical Waveguides

Finite-element analysis employing the scalar and vector H-field formulations and with the aid of the perturbation technique is used to calculate the TE-TM complex propagation characteristics of integrated optical devices in gallium arsenide, lithium niobate, and silica fiber, incorporating a lossy metal cladding. The propagation and attenuation properties of several types of metal-clad planar optical waveguide, which exhibit surface-plasmon properties for the TM polarization, are reviewed, and the modal loss caused by the metal cladding in a titanium-diffused lithium niobate electro-optic directional coupler modulator, an indium gallium arsenide phosphide-based TE-TM optical polarizer, and a submicron metal-clad silica fiber suitable for near-field optical scanning microscopy is calculated.     

The role of the ohmic contact on the efficiency of gallium arsenide radiation detectors

It has recently been found that in gallium arsenide radiation detectors injecting ohmic contacts impede charge collection efficiency to get 100%, since breakdown occurs as soon as the electric field reaches the contact itself. In the present contribution, this phenomenon is investigated by comparing two sets of ohmic contacts realized by different technological procedures. While the overall defective state results to be nearly the same for both contacts, their performance significantly differs. Deep level junction spectroscopy shows that the defects are the same in both sets whilst there is much difference in density between a few of them.     

Photo-carrier and Electronic Studies of Silicon-Doped GaAs Grown by MBE Using PCR

Photo-carrier radiometry (PCR) has been used to study the distribution of impurities and the lattice damage in silicon-doped gallium arsenide in a noncontact way. The results from the PCR study are correlated with Hall effect measurements. Samples for this study were grown by molecular beam epitaxy. Of all possible parameters that can be manipulated, the silicon effusion cell temperature was the only one that was varied, in order to obtain samples with different silicon concentrations. The distribution of impurities was obtained by scanning the surface of each sample. The PCR amplitude and phase images were obtained as a function of the x–y position. According to the PCR images, it is evident that the impurities are not uniformly distributed across the sample. From these images, the average value of the amplitude and phase data across the surface was obtained for each sample in order to study the PCR signal behavior as a function of the silicon effusion cell temperature.     

Suppression of parasitic backgating by hydrogenation of ion-doped gallium arsenide structures

It has been established that hydrogenation of ion-doped gallium arsenide structures can be used to suppress parasitic backgating. Curves describing the degree of suppression of the backgating as a function of the hydrogenation regimes are given. The observed dependence is evidently caused by the formation and decay of hydrogen complexes with deep centers. Pis’ma Zh. Tekh. Fiz. 25, 37–41 (July 12, 1999)     

Metalorganic molecular beam epitaxy of GaN and Al(Ga)N on GaAs(001) studied using laser reflectometry and reflectance anisotropy spectroscopy

We report the growth of GaN and AlGaN films on GaAs (0 0 1) substrates in the temperature range 400–800 °C by metalorganic molecular beam epitaxy. An r.f. plasma nitrogen source was used in conjunction with triethylgallium and ethyl-dimethylamine-alane group III sources. Growth was initiated using either a low temperature AlN buffer layer or a graded arsenide-nitride buffer layer. The growth was monitored in real time using in-situ laser reflectometry. The temperature dependence of growth rates for the nitride layers are compared with their arsenide analogs. The relative growth rate of gallium nitride/gallium arsenide from triethylgallium was found to be in the range 54–60%, the Ga incorporation rates are closely comparable when the higher density of GaN is taken into account. The range of growth temperatures for gallium nitride extends to higher temperatures compared with gallium arsenide probably due to lower evaporation rates of Ga bound to the nitride surface. Reflection anisotropy spectra indicate that atomic nitrogen readily reacts with the GaAs (0 0 1)-c (4 × 4) As-stabilized surface at temperatures as low as 400 °C but without the gross faceting that has been observed at higher temperatures.