The growth of gallium arsenide films from a thin solution layer between substrates

The method of GaAs film growth from a solution between two substrates was considered. The calculated thickness as a function of growth temperature and distance between substrates was in a good agreement with experimental results. The investigation of the film roughness as a function of cooling rate, distance between substrates and their orientations was fulfilled. Electrical properties of the films as a function of substrate orientations in the interval (100)–(111)–(011) were demonstrated. The possibility of application of this method for the investigation of film doping as a function of temperature and growth rate was shown.     

Hopping conduction in Cr-doped amorphous gallium arsenide films

Amorphous Cr-doped GaAs has been prepared by rf sputtering and the dc conductivity measured at fields up to 10⁷ V/m and temperatures down to 80 K. The results are explained in terms of field-assisted hopping. Effects of isothermal annealing at temperatures up to 200°C are studied. The studies are repeated and the results compared with undoped a-GaAs. Room temperature resistivities of a-GaAs: Cr, a-GaAs and polycrystalline GaAs are also compared. The recrystallization temperature for a-GaAs films is determined to be between 320°C and 340°C.     

The behaviour of copper on gallium arsenide

Cu has been reported to diffuse rapidly in GaAs at low temperatures (2.3×10^-5 cm² s^-1 at 600°C). The rapid diffusion is attributed to the interstitial movement of Cu atoms. The present investigation was undertaken to examine preferential diffusion of Cu⁺ along dislocations and grain boundaries in GaAs. The experiments consisted of depositing ⁶⁴Cu on a GaAs water surface, annealing in vacuum, and observing the Cu distribution by autoradiography. From these observations no preferential diffusion along dislocations or grain boundaries was detected in SI GaAs annealed between 600 and 1000°C. In the sample annealed above 800°C, the deposited Cu reacted with the GaAs forming a liquid on the sample surface, which solidified into complex Cu-Ga-As compounds. The liquid also produced Cu-rich pipes which extended through the GaAs wafer.     

EPD investigation in LEC-grown silicon-doped gallium arsenide

The EPD distribution is investigated in silicon-doped LEC-grown gallium arsenide crystals, 30 ÷ 40 mm in mainbody diameter and weighing within 300 ÷ 500 grams. The silicon-doping-dependent hardening effect, previously observed in S-doped and Bridgman grown silicon-doped gallium arsenide is here confirmed. The EPD decreasing with silicon-doping increase is observed to be less pronounced than in the case of S-doped and Bridgman grown silicon-doped samples and possible reasons for this different behaviour are discussed. In any case, a large microprecipitate density together with the EPD reduction appears as a clustering of shallow-pits around dislocation pits.     

Micromorphology and defects of non-doped gallium arsenide layers

Electron microscopy was used to study non-doped GaAs layers obtained in a chloride system Ga-AsCl₃-H₂. Electron concentrations is 10¹³–10¹⁵ cm⁻³, mobility at liquid nitrogen temprature reaches 200000 cm²/v. sec. It is shown that a fraction of the growth surface taken with (110) faces is less for films with less electron concentration. The main type of defects in pure GaAs layers is precipitates at pinning centres of growth steps. Estimations based on microdiffraction patterns and irradiation effects show that the impurity concentration in them is 10¹⁶–10¹⁹ cm⁻³. The impurity in precipitates is assumed to be electrically non-active, mainly, in interstitial positions.     

Precipitation of supersaturated chromium solutions in gallium arsenide

Transmission electron microscopy has been used to investigate precipitation processes in gallium arsenide doped with chromium and Cr₂O₃. Whatever the doping technique, at concentrations of chromium 4 × 10¹⁶ cm⁻³ the solid solution was observed to contain precipitates which grew, at least partially, due to the migration of substitutional atoms and their transformation into the precipitates. The process is accompanied by generation of vacancies from dislocation loops.     

Liquid phase epitaxial growth of undoped gallium arsenide from bismuth and gallium melts

Electrical properties of undoped GaAs layers grown from Ga and Bi melts under identical conditions are compared as a function of growth temperature and pregrowth baking time. Identification of residual shallow donors and acceptors is performed by means of laser photoelectrical magnetic spectroscopy and low temperature photoluminescence. It is shown that a change of solvent metal results in complete alteration of major background impurities in grown epilayers due, mainly, to changes of distribution coefficients of these impurities. High purity, low compensation n-GaAs layers can be grown from Bi melt (epilayers with the Hall mobility of electrons μ77K ≈ 150000 cm²/V · sat n = 2.5 · 10¹⁴ cm⁻³ has been grown).     

Tin segregation and donor compensation in melt-grown gallium arsenide

Radio-tin-doped single crystals of GaAs have been grown by the LEC technique from melts of varying composition. Carrier concentration and Sn distribution determined by radio-counting and autoradiography are reported and analysed to show that Sn-related acceptors are incorporated to give a compensation ratio of N_A/N_D = 0.24+-0.03 independent of doping level and of melt composition. These concentrations are significantly in excess of a non-Sn-related residual acceptor - believed to be C_As - which is shown to be present in the crystals at a level of 1.6x10¹⁶ cm^-3. Modified Sheil plots are used to show that the melt composition appears to move progressively toward As-richness as growth proceeds. The distribution coefficient for tin in crystals growing from a stoichiometric melt is determined to be 4.0x10^-3.     

Growth of gallium antimonide epitaxial layers on indium arsenide substrates

In the present work the possibility is demonstrated of growing gallium antimonide epitaxial layers on indium arsenide substrates using the liquid phase epitaxial (LPE) method. The influence is nivestigated of the growth conditions on the morphology of the surface and interface of the epitaxial structures InAs GaSb. The optimum technological regimes for growth of heterostructures in the system InAs GaSb are found.     

Low-temperature atomic assembly of stoichiometric gallium arsenide from equiatomic vapor

The low-temperature atomic assembly of homoepitaxial GaAs thin films on the (0 0 1) surface has been investigated using molecular dynamics with a Stillinger–Weber potential energy function. During equiatomic vapor deposition, crystalline growth was observed for substrate temperatures above 35% of the melting temperature. Below this temperature, the critical epitaxial thickness began to rapidly decrease as defects were increasingly incorporated and eventually nucleated an entirely amorphous structure. The atomic assembly mechanisms of arsenic dimer incorporation, as well as gallium vacancy formation, were studied just above the amorphous/crystalline growth transition temperature. The adsorption of arsenic dimers was found to show dependence upon the orientation of the deposited molecule. Atomic processes responsible for the formation of the gallium vacancy defects were observed, and the influence of growth temperature on defect formation was also identified.     

Growth temperature dependence in molecular beam epitaxy of gallium arsenide

Epitaxial layers of GaAs were grown on GaAs(100) at substrate temperatures ranging from 400° to 600°C by molecular beam epitaxy. Surface structures of the substrate and the epitaxial layers were investigated by means of low-energy electron diffraction. Two new structures of c(4 × 4) and c(8 × 8) were observed from layers grown at the low temperature of 400°C. The electrical and optical properties of layers doped with Si were investigated by measurement of Hall effect and photoluminescence as a function of growth temperature. It is found that a semi-insulating layer is grown below a critical temperature, and the layer is useful as a buffer layer for GaAs FET's. Variation of carrier concentration was observed near the interface between layers grown at different temperatures under a constant Sn beam flux. The effect is attributed to defect-induced segregation of Sn.     

Crystallinity of the mixed phase silicon thin films by Raman spectroscopy

Raman spectra of the mixed phase silicon films were studied for a sample with transition from amorphous to fully microcrystalline structure using four excitation wavelengths (325, 514.5, 632.8 and 785 nm). Factor analysis showed the presence of two and only two spectrally independent components in the spectra within the range from 250 to 750 cm^?1 for all four excitation wavelengths. The 785 nm excitation was found optimal for crystallinity evaluation and by comparison with surface crystallinity obtained by atomic force microscopy, we have estimated the ratio of integrated Raman cross-sections of microcrystalline and amorphous silicon at this wavelength as y = 0.88 ± 0.05.     

Structural,compositional and optical properties of gallium selenide thin films doped with cadmium

Polycrystalline cadmium doped gallium selenide thin films were obtained by the thermal co‐evaporation of GaSe crystals and Cd grains onto glass substrates. The structural, compositional and optical properties of these films have been investigated by means of X‐ray diffraction, energy dispersive X‐ray analysis and UV‐visible spectroscopy techniques, respectively. Particularly, the elemental analysis, the crystalline nature, the energy band gap, the refractive index, the dispersion energy and static dielectric constant have been identified. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct forbidden energy band gap of 1.22 eV. The cadmium doping has caused a significant decrease in the values of the energy band gap and in all the dispersive optical parameters, as well. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Device quality epitaxial gallium arsenide grown by the metal alkyl-hydride technique

Good vapour-phase epitaxial gallium arsenide on gallium arsenide can readily be obtained using trimethylgallium and arsine. The system is rapid and economical to use. Undoped material can be n or p-type with a carrier concentration of less than 5 × 10¹⁵ cm^?3. The best n-type material had a room temperature mobility of 6260 cm² sec^?1 V^?1, and for the best p-type material it was 385 cm² sec^?1V^?1. Material can be controllably doped n-type with sulphur. Multiple sub-micron n⁺ and n on p layers have been grown and used to fabricate Schottky barrier field effect transistors (FET). Material with good photocathode properties was grown by doping strongly p-type with dimethyl zinc.     

Simulation of the eddy current sensing of gallium arsenide Czochralski crystal growth

The feasibility of eddy current sensing of (1) the melt surface position and (2) the liquid-solid interface shape of 3-inch gallium arsenide crystals being grown by the Czochralski technique has been investigated using an axisymmetric finite element method. The results show clearly that differential sensor designs operating at high frequency ( ≈ 1 MHz) are very sensitive to the distance between the sensor and the surface of the melt providing the opportunity to precisely monitor and control this important variable of the growth process. The calculations also show a weaker effect of interface shape upon the imaginary impedance component at lower frequencies (1–10 kHz). Its physical basis is due to the different skin depths of solid and liquid GaAs. We show that a sensor's response to this interface effect can be enhanced by appropriate design of the differential sensor's pick-up coils.     

Nature of dislocations promoting growth in liquid phase epitaxy of gallium arsenide

Dislocations promoting growth in the course of liquid phase epitaxy (LPE) of GaAs layers on GaAs substrates are analysed by X-ray topography. The Burgers vectors are determined by comparing double-crystal back-reflection images with calculated misorientations taking into account surface relaxation. Any dislocation which generates a spiral of elementary steps is found to have a Burgers vector component parallel to the macroscopic growth direction. The nature of these growth promoting dislocations may be between pure screw and pure edge type. Defects which might be responsible for the generation of the observed concentric growth step patterns are below the detection limit of current X-ray topography.     

The incorporation of Cr into gallium arsenide grown by the LEC method

To investigate the incorporation of Cr into LEC GaAs, we have grown nine Cr-doped GaAs crystals where the dopant is labelled with radio-tracer ⁵¹Cr. A thermodynamic model is developed to describe the segregation behaviour in which the distribution coefficient of the Cr is a function of the arsenic activity in the melt. The analysis shows that either the congruent melt is ˜ 2% richer in Ga than the stoichiometric composition or, much more probably, that a significant amount of Ga is lost into the B₂O₃ encapsulant. The latter postulate is shown to be consistent with recent studies by Emori et al. [Japan. J. Appl. Phys. 24 (1985) L291].     

SIMS and Raman characterizations of ZnO:N thin films grown by MOCVD

Nitrogen was incorporated into ZnO films grown by metalorganic chemical vapour deposition (MOCVD) on ZnO substrates using DMZn-TEN, tert-butanol and diallylamine, respectively, as zinc, oxygen and doping sources. The carrier gas was either hydrogen or nitrogen and the partial pressure ratio (R_VI/II) was varied in order to favor the nitrogen incorporation and/or reduce carbon related defects. The ZnO films have been characterized by Micro-Raman scattering and SIMS measurements. SIMS measurements confirm the nitrogen incorporation with concentrations extending from ∼10¹⁹ cm⁻³ to ∼4×10²⁰ cm⁻³. Raman spectra show nitrogen local vibration modes in films grown at low R_VI/II ratio and using H₂ as carrier gas. However, a vibration band attributed to carbon clusters dominates the Raman spectra for films grown with N₂ carrier. The contribution of N complexes was discussed. The strain was calculated for the as-grown and annealed films and it changes from tensile to compressive after annealing.     

Effect of electrical field on growth of gallium arsenide layers from vapour phase

The effect of electrical fields on the growth rate and morphology of gallium arsenide layers in the GaAs AsCl₃ H₂ system is investigated. The fields both parallel and perpendicular to the substrate surface are used. It is found that application of the parallel field results n increase of growth rate of (111)A face but does not change that of 2° (001). The morphology of layers grown in such a field is better than that grown without any. The application of perpendicular field results in decrease of growth rate for both crystallographic orientations, the layer morphology worthening. In both cases the effect is greater when the substrate has a negative potential. Possible mechanisms of the field influence on the growth rates of gallium arsenide layers are discussed such as: supersaturation decrease because of nucleation in vapour phase and the change in the rates of surface processes.