Structure defects investigation of GaAs and AlxGa1−xAs epitaxial layers

The paper is concerned with the results of investigation of structure defects in gallium arsenide and Al_0.3Ga_0.7As epitaxial layers. It was found that structure defects in layers under investigation are responsible for the excess component of the Schottky diode's reverse current.     

Investigation of GaAs—InyGa1−yPzAs1−z–InxGa1−x-As grading heterojunctions formation

The initial stages of growth of GaAs–InGaAsP_var–In_xGa_1−xAs heterostructures (x = 0.1 and 0.17) were investigated for the equilibrium-cooling method of LPE growth. Similar investigations were carried out for GaAs–InGaAsP_var–In_0.05Ga_0.95As heterocompositions, but for the step-cooling technique. The scheme of growing of In_0.17Ga_0.83As films of GaAs substrates with several intermediate buffler InGaAsP_var layers is represented. These heterostructures were shown to have less than 10⁶ cm⁻² dislocation density on the overall area of the film (> 2 cm²).     

Liquid phase epitaxial growth and characterization of thin In1−xGaxAsyP1–y layers lattice-matched to InP

Growth studies enabled the deposition of In_0.71Ga_0.29As_0.68P_0.32 single quantum well structures with InP or In_0.88Ga_0.12As_0.26P_0.74 confinement layers lattice-matched to (001) InP by liquid phase epitaxy (LPE). Well widths in the order of 50–100 Å have been achieved using a conventional step cooling technique. The physical characterization has demonstrated the capability of the employed method to produce multilayered heterostructures which display confined particle states; quantum mechanically induced blue-shifts of the low temperature PL-emission up to 125 meV were measured. A remarkable reduction of the FWHM values of the shifted PL peaks was attained by optimization of the growth conditions.     

Calculations of homogeneous region in Ga1−xAlxAs and GaAs1−xPx ternary solid solutions

Ternary solid solutions of A^IIIB^V compounds are considered as pseudobinary A(x)^IIIB(x)^v compounds, where the behaviour of A(x)^III and B(x)^v pseudoatoms is quite similar to A^III and B^v atoms in a binary A^IIIB^v crystal. Weak dependence of point defect contribution into Gibb's energy of A^IIIB^v crystal on its defect nature, random character of ternary solid solutions of A^IIIB^v compounds allow to use already for binary compounds developed formalism in the determination of component thermodynamic potentials of solid solution. Basing on literature data for the equilibrium solidus of AlAs the approximation for the temperature dependence of thermodynamic potential of an AB quasimolecule in A^IIIB^v crystal is revised. This result together with the well-known parameters for the equilibrium liquidus in Ga–P, Ga–As, and Al–As systems were used for calculations of the nonstoichiometric factor at the boundary of a homogeneous region in Ga_1−xAl_xAs and GaAs_1−xP_x ternary solid solutions. The results are compared with the known literature data.     

Magnetically induced rhombohedral distortion in the UxTh1−xSe and UxY1−xSe solid solutions

Solid solutions of U_xTh_1−xSe for x = 1.00 ÷ 0.80 and the solid solutions of U_xY_1−xSe for x = 1.00 ÷ 0.60 were studied by the X-ray diffraction over the temperature range 100 ÷ 200 K. In both systems rhombohedral distortions of the cubic rock-salt crystal structure was observed below the Curie temperatures. The temperature and composition dependences of the rhombohedral angle ω of the rhomboedral cell and the \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{c' - a'}}{{a'}} $\end{document} ratio were determined.     

Low-temperature growth of epitaxial layers of ZnSe1−xTex solid solutions

The layers of ZnSe_1−xTe_x (0 < x < 1.0) solid solutions have been grown by liquid-phase epitaxy in a closed tube at 620–680 °C. Zinc chloride served as a solvent. ZnTe and ZnSe crystals were used as sources and substrates with orienting surfaces (110) and (111) for ZnSe and (110) for ZnTe. The composition of the grown layer was specified by the relative content of the ZnSe and the ZnTe in the solution and was controlled by X-ray analysis. The position of the exciton bands in the photoluminescence spectra of ZnSe_1−xTe_x over the interval 0.3 < x < 1.0 is in agreement with the free exciton energies calculated for these compositions. Relatively low-ohmic (of about 10² Ω cm) epitaxial layers of ZnSe_1−xTe_x solid solutions were grown.     

A study of a fast ionic conductor–Ag1−xCuxI

The Conductivity of AgI–CuI system has been studied. Two molar ratios of the system Ag_1–xCu_xI with x = 0.05 and 0.15 have been taken. The transition temperatures are observed with conductivity measurements.     

SixGe1−xGaAs Heterojunction IMPATT-Diodes

Experimental research IMPATT-diodes on heterostructures Si_xGe_1−x-GaAs showed that the interphase boundary is noted with high thermal and radiation resistance. It is shown that such diodes are an equivalent alternative IMPATT-diodes with type of Schottky barrier.     

AlxGa1−xAs LPE growth

Al_xGa_1−xAs LPE growth was studied within the temperature range of 930–900°C with Al concentrations in solutions from 0.04 to 2.4 at.%. AlAs concentration in layers has been shown to grow with the cooling rate increase of solution. Interface and volume nucleation parameter dependence of K_i and K_v and formation time t_f on Al concentration in Ga solution have been found. Addition of Al to Ga solution increases critical values of As supersaturation (supercooling) and, as a result, increase in thickness of Al_xGa_1−xAs layers compared with GaAs layers have been determined in spite of As concentration lowering in Ga solution.     

Quantitative analysis of Bi1−xSbx

The chemical composition of Bi_1-xSb_x alloys is determined by means of square-wave polarography, density measurements, measurements of the electron backscatter coefficient, and electron probe microanalysis. These experimental methods are discussed with respect to their results. At 10 keV, the electron probe microanalysis allows the determination of any antimony concentration without corrections (c_Sb = k_Sb).     

A complex method for structural investigation of GaAs1−xPx epitaxial layers grown on GaAs substrates

A universal X-ray diffractometer is used for the structural complex investigation of GaAs_1−xP_x epitaxial layers, grown on the (100) face of GaAs substrate. Information is obtained from the analyses of diffraction patterns for some qualities of the epitaxial layers: crystallographical orientation, composition, thickness, as well as structure of the transition region. The suggested complex method has important advantages against the standard Laue method. It is far easier express and convenient for serial investigations.     

Liquidphasen-Epitaxie von Si-dotiertem AlxGa1−xAs

The liquidus and solidus isotherms of the quaternary phase diagram Ga—Al—As–Si have been estimated at 850 °C and N_Si = 0.04 and 0.1. Epitaxial layers were grown and the influence of silicon on the growth rate was investigated. Hall-effect measurements give informations on the dependence of the carrier concentration on the silicon content in the melt. The donor ionization energies vary from 32 to 69 meV and are diminished proportional to N.     

Polytypes of the system Fe1−xS

The structures of Fe_1−xS (0 < x < 0.135) are members of a family of derivative structures in the sense of Megaw. The NiAs structure as aristotype is the simplest and most symmetrical member of this family. The other polytypes of Fe_1−xS may be derived as hettotypes by lowering the symmetry. The loss of symmetry in changing from the aristotype to the hettotype may be of various kinds: small displacements of Fe and S atoms from the NiAs positions and/or Fe vacancies in some atomic planes occur. The structures of the system Fe_1−xS are interpreted as OD structures consisting of OD layers. The symmetry relations of the structures of FeS and Fe₇S₈ are described by OD groupoid families. Polymorphism, twinning and stacking faults are explained on this basis.     

Microhardness studies of K1−xRbxCl crystals

The microhardness measurements have been made on pure crystals of KCl, RbCl and mixed crystals of K_1−xRb_xCl. Microhardness varies non-linearly with composition being maximum near at the eqimolar composition. Microhardness values calculated from lattice parameter data are in good agreement with experimental data. The difference in the size of the ion constituting the mixed system is responsible for the internal strains giving rise to imperfections and inturn responsible for the non-linear variation of microhardness with composition.     

Vickers indentation hardness of Hg1−xCdxTe

The Vickers indentation hardness of Hg_1−xCd_xTe has been measured as a function of composition x using monocrystalline samples of Bridgman and THM crystals and polycrystalline starting material at room temperature. The microhardness varied between 220 MPa (x=0) and 440 MPa (x=1), showing a maximum of 850 MPa at x ∼ 0.75, and was different between monocrystalline and polycrystalline samples. The “hardening rate” dH/dx is strongly dependent on the composition range and is discussed in context with solid solution hardening due to elastic interactions of solute atoms with gliding dislocations and ordering effects.     

Magnetic properties of the CrSxTe1−x (x = 0−0.2) solid solutions

On the basis of X-ray, magnetic and neutron diffraction measurements the range of solubility in the CrS_xTe_1−x (x = 0−0.2) system has been established and the magnetic phase diagram of the system has been plotted. The decrease of magnetization at low temperature and the additional reflections in the neutron diffraction patterns are associated with the formation of noncollinear magnetic structure which is characterized by the antiferromagnetic component of the magnetic moments. This component has the orthorhombic unit cell with \documentclass{article}\pagestyle{empty}\begin{document}$ a_M = \sqrt {3a_0 } $\end{document}, b_M = a₀, c_M = c₀. The character of the exchange interactions giving rise to this magnetic structure is discussed.     

Bildung und Untersuchung von SixAl1−xAs-Kristallen

Si_xAl_1−xAs is formed by chemical transport reaction of AlAs using iodine as transporting agent. The experiments are performed in sealed silica tubes in the temperature range from 900 to 1000°C. The grown platelet-shaped crystals and whiskers are investigated with x-ray diffraction, light microscopy, electron microscopy and electron-probe microanalysis. The mechanism of growth is discussed.     

Bildungsbedingungen und Struktur dünner Bi1−xSbx-Schichten

Thin polycrystalline Bi_1−xSb_x films in oriented state were deposited by flash evaporation techniques and by catode sputtering. In dependence on the conditions of formation the structure of these films was analysed by means of transmission electron microscopy, electron diffraction and electron beam microanalysis. Estimating the orientation, quality of surface and largeness of the average diameter of the crytallites the flash evaporation technique is superior to the catode sputtering under the experimental conditions chosen in this investigation. The Bi:Sb proportion does not change in comparison with the target, material of the source respectively, during the formation of the film.     

Chemical lap polishing of PbTe and Pb1−xSnxTe crystals

Chemical lap polishing of PbTe and Pb_1−xSn_x Te crystals is investigated. A mixture of potassium hexacyanoferrate (III), sodium hydroxide, glycerol and water is used as a polish. The effect of various parameters of the process on the quality of the surface and on the rate of material removal is studied. The quality of the surface is strongly is strongly affected by the composition of the polish. The roughness increases with rising sodium hydroxide concentration but decreases with rising glycerol concentration. If the molar ratio of sodium hydroxide and potassium hexacyanoferrate (III) exceeds the value 0.5 etch figures are formed. The rate of material removal largely depends on the velocity of the relative movement between specimen and cloth, the rate of supply of polishing solution and on the concentration of sodium hydroxide.