Reduction of thermal oxide desorption etching on gallium arsenide

We describe an in-situ method for inhibiting surface roughening during the thermal removal of the GaAs native oxide layer based on a thin sacrificial GaAs film deposited on top of the native oxide layer prior to sample heating. The required thickness of the sacrificial film is calculated to be of the order of 5 nm, fitting well with the experimental results. Atomic force microscopy and reflection high-energy electron diffraction indicate improvement in the surface smoothness, from an RMS roughness of 2.3 nm to 0.5 nm, while inhibiting the inherent pit formation commonly associated with thermal desorption.     

Passivating gallium arsenide surface by gallium chalcogenide

We have studied the protective properties of thin films of gallium selenide formed by the method of heterovalent substitution on the surface of GaAs substrates. The data of transmission (Hitachi H-800) and scanning (JEOL JSM-638 OLV) electron microscopy showed that GaAs substrates treated with selenium vapor produced a more pronounced orienting action on the subsequent deposition of GaAs as compared to the substrates covered with a natural oxide. The processing of a GaAs substrate in selenium vapor followed by the removal of the resulting Ga₂Se₃ layer increases the degree of smoothness of the substrate surface on the atomic level.     

Electrodeposition kinetics of gallium arsenide

A kinetic model has been developed for the electrodeposition of GaAs from solution containing reducible ions of both constituents and is based on the generalised Butler-Volmer equation. The effect of hydrogen ion concentration and activities of ions on the total current density is studied. Voltammograms corresponding to various values of hydrogen ion concentration and activities of ions are constructed by the computer simulation technique.     

Stacking-faults in tellurium-doped gallium arsenide

Samples of bulk-grown gallium arsenide single crystals, taken from both static freeze, and Czochralski ingots doped to a high level with tellurium, have been examined using transmission electron microscopy. Observation of single and multiple stacking-fault layers which have fault vectors of the kindR=a/3111 is reported. It is shown by diffraction contrast experiments that the stacking-fault defects are extrinsic. They are thought to be rafts of tellurium substituting for arsenic in {111} planes. The prevalence of the observed layer defects correlates well with the increase in carrier concentration in certain regions of the crystals.     

Characterization of defects in gallium arsenide

It is well-known that the properties of semiconductor materials including gallium arsenide are controlled by defects and impurities. The characterization of these defects is important not only for better understanding of the solid state phenomena but also for improved reliability and performance of electronic devices. We have been investigating the defects in gallium arsenide for several years using deep level transient spectroscopy, photoconductivity, transient photoconductivity, photoluminescence etc. Results drawn from our recent studies are presented here to illustrate some of the problems concerning transition metal impurities, process-induced defects, occurrence of intracentre transitions and metastability of deep levels in gallium arsenide.     

Chromium oxide nanolayers on gallium arsenide

Ultrathin chromium oxide layers (nanostructures) are grown on (100) and (110) GaAs substrates by molecular layering (atomic layer deposition). The effect of process conditions on the layer composition and growth mechanism is analyzed. The dielectric properties of the layers and the quality of the dielectric-semiconductor interface are evaluated.     

Deformation of single crystals of gallium arsenide

Deformation of single crystals of gallium arsenide is reported in bend and tension up to 1000° C whilst maintaining stoichiometry in an arsenic atmosphere. Surface defects and impurity segregation are shown to be dislocation sources. The dislocation density is low enough, however, to show large yield drops which are analysed in detail. Strains of 39% are possible. The activation energy for dislocation movement is increased by heat-treatment owing to an increase in point defect population.Electron microscopy shows that the predominant slip systems are {111} 110 and the majority of dislocations have b=a/2 110, the axes lying along 110 and 112 directions. Sub-cell formation occurs with sub-boundaries lying along 110 directions.     

Anisotropic etching of SiC whiskers

We have demonstrated a method of producing nanoplatelets or complex well-ordered nanostructures from silicon carbide (SiC) whiskers. Preferential etching of SiC whiskers in a mixture of hydrofluoric and nitric acids (3:1 ratio) at 100 degrees C results in the selective removal of cubic SiC and the formation of complex structures resembling a pagoda architecture. Possible mechanisms governing selective etching are discussed. Reproducible results on SiC whiskers manufactured in different laboratories suggest that the self-patterning phenomena are common in SiC whiskers, and the same electroless etching procedure can be used to synthesize various complex nanostructures from more conventional nano- and microscale objects for use as building blocks in the fabrication of sensors, cellular probes, and electronic, optoelectronic, electromechanical, and other devices.     

Modeling of silicon diffusion in gallium arsenide

A model is developed and a study is performed for amphoteric diffusion of silicon in gallium arsenide. A comparison of predictions with experimental data indicated adequacy of the devised model and high efficiency of the numerical method for solving the diffusion equation.Belorussian State University, Minsk. Minsk Radio Engineering Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 567–572, November, 1993.     

Preparation of single phase gallium nitride from single crystal gallium arsenide

An analysis has been conducted on the final products obtained in attempts to prepare single phase gallium nitride from single crystal gallium arsenide. When the intermediate oxide phase was nitrided in pure ammonia it was found that (i) the lowest temperature at which rate of conversion of-Ga₂O₃ to GaN became significant was in the range 600 to 700°C, (ii) over the temperature range 700 to 1000°C GaN was found to be the only crystalline phase present, (iii) above 1100°C-Ga₂O₃ was the main constituent. In comparison, when the oxide phase was nitrided in a 50% NH₃-50% N₂ atmosphere it was found that (i) the lowest temperature at which conversion to GaN occurred lay between 700 and 750°C, (ii) there was only a narrow range of temperatures, 750 to 870°C, in which the final products were found to contain GaN as the only crystalline phase, (iii) samples nitrided above 870°C exhibited both GaN and-Ga₂O₃ phases, the proportion of-Ga₂O₃ increasing with increasing temperature.     

Quantitative measurement of impurities in gallium arsenide

The chemical concentrations of Be, O, Si, S, Zn and Sn have been measured in epitaxial layers of GaAs grown by the molecular-beam and vapour-phase techniques and also in bulk crystals grown by the Bridgman technique. Spark source mass spectrometry calibrated using atomic absorption spectrometry was used to give quantitative results with high detection sensitivities for a large range of elements. For doped layers containing no significant background impurities (<10¹⁶ cm^–3) the chemically determined dopant concentrations relate directly to the measured free carrier concentrations in the range 10¹⁶ to 10¹⁹ cm^–3. Impurity elements such as O, Ti, Fe, Mo and W act as trapping centres and must be considered when interpreting the electrical results.     

Native oxide glasses for indium gallium arsenide

Epitaxial films of indium gallium arsenide on indium phosphide are important for optoelectronic applications in the 1.0 to 1.7 μm wavelength region. Oxide glasses having essentially the same metal ratios as the epitaxial films, thermal expansion coefficients near 7.5 × 10^?6 and glass transition temperatures from 560 to 640°C have been prepared. They can be sputtered readily as water insoluble amorphous films that can be etched easily, even after prolonged heat treatment at 600°C, and are useful for thermal diffusion masks.     

Characterization of deep levels in semi-insulating gallium arsenide

Two traps with activation energies ofE _c – 0·47 eV andE _v + 0·79 eV have been detected in semi-insulating GaAs:Cr through optical transient current spectroscopy (otcs) in the temperature range 300–450 K. The latter trap gives rise to rising current transients which result in a negative peak in theotcs spectrum. The theoretical expressions for current transients have been derived.     

Adsorption of lithium and oxygen on gallium arsenide

The adsorption of lithium on GaAs(100) and the coadsorption of lithium and oxygen were investigated by Auger electron spectroscopy, secondary emission changes and variations in the work function ϕ. Surface treatments produced an amorphous-like substrate structure which persisted throughout the study. The lithium layer grows by the Stranski-Krastanov mode and shows a work function minimum at about 0.75–0.85 monolayers. At low lithium coverages oxygen adsorbs preferentially in “on-top” sites and so increases ϕ; at higher coverages “underneath” sites appear to be favoured and this leads to decreases in the work function. Competition between the two types of site leads to unusual dynamic effects.     

A hydrogen-sensitive structure based on semi-insulating gallium arsenide

The response characteristics of a simple hydrogen-sensitive structure based on semi-insulating single crystal gallium arsenide with planar palladium electrodes deposited onto the oxidized substrate surface are studied. It is demonstrated that such structures exhibit a fast response to hydrogen present in the gas phase. The sensitivity can be increased by growing, prior to the electrode formation, an intermediate epitaxial GaAs film with built-in strained quantum-confined layers of InGaAs and InAs onto the semi-insulating GaAs substrate.