Analysis of Changes in the Intensity of the Intrinsic Luminescence after the Copper Diffusion into Semi-Insulating Undoped GaAs Crystals

An analysis is made of the effect of the copper diffusion into semi-insulating undoped GaAs crystals on the intensity of the intrinsic luminescence. It is shown that the copper diffusion into semi-insulating undoped GaAs crystals could lead both to an increase and to a decrease in the intrinsic luminescence intensity. Analytical expressions connecting the value and the sign of the effect observed with the recombination parameters of crystals pointed and also with the intensity of luminescence excitation are obtained.     

Germanium Incorporation in Ga1–xInxAs LPE Layers and GaAs Bulk Crystals

Atomic absorption spectroscopy (AAS) is used to determine the Ge concentration in Ga_1–xIn_xAs and GaAs. The orientation dependence of Ge incorporation in (111)A-and (111)B oriented samples has been studied. The distribution coefficients for both the orientations were determined to be k_Ge^(111)A = 2.6 · 10⁻² and k_Ge^(111B = 1.4 · 10⁻² for Ga_1–xIn_xAs with 0 ≦ x ≦ 0.13. The differences between the two orientations are explained with the aid of the band bending model. Doping gradients in thick epitaxial layers and along crystal length of polycristalline TGS-grown GaAs ingots have been investigated too. In Ga_1–xIn_xAs layers any Ge concentration gradient couldn't be observed, but in TGS compact crystals Ge concentration increases with crystal length because the melt composition changes significantly during solidification. The results are compared with those of electrical measurements.     

Silicon Doping of GaAs Single Crystals

The silicon doped GaAs single crystals were grown by means of a horizontal Bridgman method. The relation between the free carrier concentration and silicon concentration determined by chemical analysis was examinated.     

Magnetoplastic Effect in Te-Doped GaAs Single Crystals

Crystallography Reports - The influence of a dc magnetic field on the motion of growth dislocations with a density of (0.7–7.0) × 104 cm–2 and the electron density in the range of...     

Radiation Defects Research in Single Crystals of Lithium Niobate

An information is given on the kinetics of developing ionization defects by γ-radiation, as well as on the destroying of these defects as a result of thermal treatment in oxidizing atmosphere at different temperatures. The presence of several types of ionization defects developing by γ-radiation is found out. Values of diffusion factor for each type of defects are given.     

Defects in LEC-grown Indium Phosphide Crystals Doped with Tin

Crystalline defects in Sn-doped LEC indium phosphide have been revealed by chemical etching and analyzed by TEM. Grown-in dislocations, various kinds of defect clusters and colonies of microdefects were found. The symmetrical defect clusters are shown to equate mostly with larger dislocation loops exhibiting shear components and/or other dislocation arrangements generated by a stress source which is positioned in the centre of the dislocation cluster. Those centres are often formed by a plate-like agglomeration composited of tiny inclusions and very small faulted dislocation loops. Such planarly arranged accumulations of microdefects lie on {111} planes. The direct vicinity of single threading grown-in dislocations is always enriched with tiny perfect dislocation loops and precipitates. Additionally, very large isolated interstitial-type perfect dislocation loops with b = a₀/2 〈110〉 have been found by TEM experiments. Mostly, the {110} habit plane of such loops is decorated with an high number of small dislocation loops and precipitates as a consequence of dislocation climb.     

制作压电器件氧化锌单晶的评述

氧化锌材料制作压电器件已经有很长的研究历史,自从Robert F.Service在1997年报道氧化锌可以在短波长范围实现蓝光输出后,氧化锌单晶在质量和体积方面取得了很大的研究进展。通过对比分析20世纪60年代以来氧化锌单晶压电特性的研究结果,指出迄今为止制作压电器件的氧化锌单晶仍然需要继续优化。     

Optical Investigation of Defects in p-type CuInSe2 Single Crystals

Optical absorption spectra in the photon energy range from 0.03 to 1.1 eV and photoreflectance spectra in the range of the fundamental edge are measured on p-type CuInSe₂ single crystals. Besides a dominant contribution to the absorption coefficient due to intervalence band transitions below about 0.75 eV the spectra revealed five additional structures that can be ascribed to defect induced optical transitions with characteristic energies between 0.48 and 0.72 eV. Based on a comparison of the near-edge optical absorption and photoreflectance spectra a shallow defect (donor or acceptor) with an ionisation energy of about 46 meV was identified.     

X-ray Characterization of Defect Structure in LEC Annealed GaAs Crystals

Wafers of commercially available semi-insulating (SI) Czochralski-grown GaAs crystals have been annealed at temperatures near the melting point (> 1100 °C) both for relatively short and long time and then rapidly quenched into cold water. Heat-treated crystals have been investigated by X-ray transmission diffraction topography. Cellular structure pattern of the as-grown sample is replaced by images of precipitates spread out over whole sample. This suggests that the excess arsenic condenses as As precipitates with nucleation sites not correlated with cell walls.     

Native Point Defects and Nonstoichiometry in GaAs (II) Mechanism of Formation and Degradation of Semiinsulating Properties of Undoped Gallium Arsenide Crystals

The nature of the main electron trap, EL2, in undoped semiinsulating GaAs crystals have been studied both qualitatively and quantitatively. It has been shown that point defects which, most probably, are responsible for the EL2 level are antisite As_Ga defects or (As_i V_Gs) complexes which are indistinguishable from the thermodynamic standpoint. The enthalpy and entropy of As_Ga formation according to the reaction As_As + V_Ga ⇄ As_Ga + V_As are equal to 0.5 eV and −7k, respectively.     

The Properties of Undoped InP and GaP Bulk Crystals Prepared by Floating Zone Melting

Undoped GaP and InP crystals which are produced by floating zone melting without a crucible were investigated. The background concentration was 10¹⁵cm⁻³ after several passages of the molten zone. The fundamental residual impurities are carbon and silicon penetrating into the crystals during the crystallization process. After purification, the electron mobility of GaP was 200 cm²/V. s, and for InP – 4000 cm²/Vs. The compensation decreased to 20%. A very effective purification was observed with respect to the carbon atoms, but for silicon this result is observed only after several passages of the molten zone. GaP and InP are basic materials for optoelectronic devices and it is important to investigate the possibility for production of pure bulk crystals. A proper method for this aim is the floating zone melting, where the crucible effect is removed and the influence of residual impurities is observed. In this work the influence of the number of floating zone passages on the electrical and luminescence properties of InP and GAP bulk crystals has been investigated.     

X-ray Topographic Assessment of Defects in Pure and Substituted Hexaferrite Crystals

Results of X-ray diffraction topography, in reflection and transmission scanning geometry, of flux grown single crystals of substituted and unsubstituted hexaferrites bearing composition SrGa_xIn_yFe_12-(x+y)O₁₉ (where x = 0, 5, 7, 9; y = 0, 0.8, 1.3, 1.0) are presented. Diffraction topographs reveal defects like misoriented grains, dislocations, cavities, inclusions, and the strain patterns in these crystals. The unsubstituted hexaferrites exhibit better perfection when compared to the substituted ones. The study is reported to support the results obtained by chemical etching and fractography, besides yielding additional information covering defects.     

Growth of Semiinsulating GaAs Crystals by Vertical Gradient Freeze Technique

GaAs crystals having dislocation densities of 1–2 10³ cm⁻² were grown using VGF technique. In the grown crystals Si_Ga is the dominant donor and C_As the dominant acceptor. Theoretical and experimental investigations have shown the possibilities to influence on the silicon and carbon content in GaAs. Based on these results, semiinsulating properties in the crystals could be achieved reproducibly.     

Twins in GaAs Crystals Grown by the Vertical Gradient Freeze Technique

The growth of facets and the generation of twins on <100> VGF (vertical gradient freeze technique) grown GaAs were investigated using DSL (diluted Sirtl-like etchant with light) photoetching and transmission X-ray topography. Due to the polarity of the (111) plane in GaAs, As facets are larger and more irregular than Ga facets and twins always occur on As facets. Twins are initiated at the change of boundary condition which is affected by temperature gradient and crucible shape. The mechanism of twin generation is explained by considering the edge concavity at the solid-liquid interface and the supercooling required for initial nucleation of a facet. Twins are more often produced in Si-doped crystals than undoped ones due to the constitutional supercooling.     

Etch Pit Density Distributions in Undoped and Doped GaAs Single Crystals

The undoped and doped (Si, N, In) GaAs single crystals are grown by horizontal Bridgman technique. The etch pit density (EPD) profiles were measured in transverse direction for each crystal. It was found that the shape of EPD profiles differs in dependence on the used dopant.     

On the Reasons Leading to an Appearance of Correlated and Anticorrelated Dependences of the Minority Carrier Lifetime on the Dislocation Density in Undoped Semi-Insulating “Stoichiometric” GaAs Crystals

It is shown that in undoped semi-insulating GaAs crystals grown under the stoichiometric conditions both correlated and anticorrelated dependences of the minority carrier lifetime τ on the dislocation density N_d could be observed. The above-pointed effect is connected with a slight excess of Ga atoms (then the correlated dependence τ vs Nd appears) or of As atoms (then the anticorrelated dependence τ vs N_d appears) which inevitably exists even in “stoichiometric” GaAs crystals (i.e. in GaAs crystals of “stoichiometric” composition).