Epitaxial Deposition of GaAs in the Ga(CH3)3?AsH3?H2 system (II). Investigations on the Hetero-Epitaxy of GaAs on Ge

Epitaxial GaAs layers have been deposited on (111), (110) and (100) faces of Ge by pyrolysis of Ga(CH₃)₃ AsH₃ H₂. In this paper the influence of growth conditions and the lattice difference of GaAs and Ge on the quality of epitaxial GaAs layers is described and discussed. The epitaxial layers are characterized by chemical etching, X-ray investigations, and by the observation of the surface morphology.     

Epitaxial Deposition of GaAs in the Ga (CH3)3?AsH3?H2-System (IV) Thermodynamic and Kinetic Considerations

For reactions taking place between the species Ga, As₂, As₄, AsH₃, and H₂, the equilibrium constants were calculated. The discussion indicates that factors other than thermodynamic considerations significantly influence the deposition process. Kinetic investigations demonstrate the importance of the As:Ga proportion that has to apply for perfect layer growth. The mechanism of deposition is in correspondence with a Langmuir-Rideal Model. For high substrate temperatures a homogeneous reaction in the vapour phase can-not be excluded.     

Epitaktische Abscheidung von GaAs im System Ga(CH3)3?AsH3?H2 (I) Autoepitaktische Abscheidung

Some aspects of Ga(CH₃)₃/AsH₃/H₂ pyrolysis are described. The quality of the epitaxial GaAs layers on GaAs substrates is examined by chemical etching, X-ray technique and observation of the surface morphology. The investigations show a relation between the quality of the layers and growth conditions (As/Ga-proportion, substrate temperature).     

Vapour Phase Epitaxy of GaxIn1−xAs in the Ga?In?HCl?AsH3?H2-System Using a Mixed Ga/In Source

The mixed crystal composition of Ga_xIn_1−xAs layers is analysed as a function of the composition of a mixed Ga/In source during VPE in the hydride system. Experimental results are compared with thermodynamic calculations. Both thermodynamics of the deposition reactions and thermodynamies of the souree reactions are considered in the calculations.     

Solid Solutions in the FeNbO4?TiO2 System

Thermal decomposition of freeze-dried complex oxalate precursors allows the synthesis of crystalline phases in the FeNbO₄ TiO₂ system at relatively low temperature. This system shows not only a rutiletype, but also a wolframite-type solid solution (ss), which exists at lower temperatures. The temperature of the reversible transformation wolframite-rutile decreases with increasing TiO₂ content.     

The Distribution Coefficient of Isomorphous Admixtures for KCI?KBr?H2O,K2SO4?(NH4)2SO4?H2O and KNO3?NH4 NO3?H2O Systems at 298 K

For the systems KCI KBr H₂O, K₂SO₄4-(NH₄)₂H₂O and KNO₃ NH₄NO₃ H₂ O equilibrium investigations have been performed and the distribution coefficients of isomorphous admixtures have been determined. For each solid solution the changes of the distribution coefficient D, the dependencies between the values of the real and ideal distribution coefficients and the directions of energetic changes in these systems during the co-crystallization of isomorphous and isodimorphous admixtures have been discussed.     

Temperature dependence of doping element incorporation with the chemical vapour deposition epitaxial silicon (VI) SiH4?HCl?PH3?H2 system

From comparing the incorporation behaviour of phosphorus in epitaxial silicon layers deposited from chlorosilane or silane-hydrogen-mixtures, it is theoretically concluded that silane hydrogen chloride-mixtures should behave like chlorosilane mixtures and different hydrogen chloride partial pressures do not influence the dependence of the incorporation of phosphorus on temperature. The theoretical expectation had been confirmed by experiments. For very low layer growth rates, however, there is a partial pressure range of hydrogen chloride, where the temperature dependence of the incorporation of phosphorus increases with rising partial pressure of hydrogen chloride.     

Hydrothermal synthesis of (Zr0.33 Ti0.67) O2–srilankite in the system ZrO2?TiO2?H2O?MF; (M = Na,K)

The hydrothermal synthesis in the system ZrO₂ TiO₂ H₂O MF; (M = Na, K) is discussed for the temperature range 573 K–773 K and the pressure of 100 MPa to 150 MPa. Starting with Zr- and Ti- butoxides their co-precipitated hydrolysates which had been annealed in different ways were used as initial products. The formation of mixed crystals (Zr, Ti)O₂ analogous to the rare mineral srilankite was dependent on the crystallinity and homogeneity of the initial products. 573 K and 100 MPa proved to be the most favourable conditions for synthesis. Higher temperatures (773 K) produced multiphase crystallizates of (Zr, Ti)O₂, baddeleyite, anatas, and rutile.     

Peculiarities in the X-ray Spectral Microanalysis of the Sn?Te?I System

This is an examination of the methodological specificities of the roentgenospectral microanalysis of the Sn Te I system, involving the application of a graphoanalytical method used in the analysis of ternary systems according to data calculated for the binary ones. The calculations were made on an ES 1060 computer in FORTRAN-4. The calculations are for different selection angles of the microanalyzer, and for a broad interval of values of the accelerating voltage. In this manner the method offered is applicable to any type of microanalyzer, and not only to the Cameca MS-46 used by us.     

Preparation and phase characterization of the SrCl2?EuCl2 and SrCl2?EuCl3 systems

The SrCl₂ EuCl₂ and SrCl₂ EuCl₃ systems were investigated over the full composition ranges by the Guinier powder X-ray diffraction technique. In the strontium chlorideeuropium dichloride system the solubility from the both ends of reactants was found when fast cooling of the melt was used. In the strontium chloride-europium trichloride system a solid solution for the composition region up to 20 mol per cent of EuCl₃ and two new intermediate chlorides, Sr₄EuCl₁₁ and Sr₉Eu₅Cl₃₃, were observed. The compounds crystallize in orthorhombic symmetry with lattice parameters of 7.220(2), 35.15(1), 6.790(4) and hexagonal 12.854(4) and 24.702(8), respectively.     

Liquid Phase Epitaxy of SiC in the System Si?Tb?SiC by Temperature Gradient Zone Melting (I). Investigation of Solubilities in the System Si?Tb?SiC

In the paper which is divided into three parts the liquid phase epitaxy of SiC by temperature gradient zone melting with the solvent Si Tb is discussed. In the first part the solubility of SiC at different initial compositions of the Si Tb solvent is studied in the temperature range 2000–2500 K.     

Investigations on the Quasi-binary System V2O5?Ta2O5

By chemical transport reactions, in the system V₂O₅ Ta₂O₅ another two compounds already described in literature were successfully isolated besides the two boundary phases. These are VTa₉O₂₅ and the compound VTaO₅ occurring in two modifications. The transition point of the irreversible change of modification α-VTaO₅ → β-VTaO₅ was determined as 1153 ± 5 K in a quite good agreement with values cited in the literature.     

Effect of Particle Size on the Ice Nucleating Ability of AgI?AgBr?CuI System

The effect of particle size on the ice nucleating behaviour of AgI-AgBr-CuI system has been studied for the first time. Six samples of different molar ratios and five sizes in each sample are considered in the present study. It is found that the nucleation temperature is the highest for particle size in the range of 60 ± 5um.     

Liquid phase epitaxy of SiC in the system Tb?Si?SiC by temperature gradient zone melting (III). Epitaxial layer properties

In the present work the electrophysical and structural properties of the SiC epitaxial layers grown by the temperature gradient zone melting method in vacuum conditions is considered. Some correlations between the epitaxial layer properties and the process conditions are observed. It is shown that the performence of the growth process in vacuum leads to a significant improvement of the layer quality, if one observes some requirements – how to decrease significantly the number of the second phase inclusions and how to improve the structural perfection of the layers.     

On the kinetics of the decomposition of ternary Al-Zn(6at.%)?Mg(X) and Al?Mg(X)?Si(Y) alloys

Investigations on Al-Zn(3)-Mg(X) alloys gave the rather surprising result that the migration energies depend on the physical quantities (resistivity, Young's modulus) and the ageing time used. Therefore it is the aim of this paper to test, if similar effects occur using other ternary alloys and additional measuring methods. The ageing kinetics of 7 Al-Zn(6)-Mg(X) alloys are examined by isothermal measurements of resistivity, Young's modulus, change of length, and microhardness over a relatively long time interval of about 3 h within the temperature range from 20°C to 90°C.

• 1 The activation energies got for the Al-ZN(6)-Mg(X) alloys depend on the physical quantity as well as on the ageing time used within the temperature range from 20°C to 40°C as known from the Al-Zn(3)-Mg(X) alloys.
• 2 The activation energies obtained for the Al-Zn(6)-Mg(1.3) alloy in the temperature interval from 50°C to 90°C decrease monotonously with increasing time for the measuring methods considered.

These results different with respect to those two temperatur ranges are probably caused by a change of the decomposition mechanism. Below 40°C presumably several kinds of clusters are formed in the beginning of the decomposition, but above 50°C probably only one sort of clusters should grow. The late stage of ageing should be caused mainly by the diffusion of VZn₂ complexes (E^M = 0.21 eV) in the temperature range investigated, since 0.2 eV holds for that stage. – Finally the results of the investigations of the kinetics of some Al-Mg(X)-Si(Y) alloys are discussed by means of the jump model.     

X-ray powder diffraction investigations of solid solutions with limited miscibility in the KNO3?NH4NO3?H2O system at 298 K

The measurements of crystal lattice parameters (a, b, c) were conducted and the volumes (v) of unit cells of solid solutions forming in the system KNO₃ NH₄NO₃ H₂O at 298 K were calculated. It was established that in this system at 298 K two series of solid solutions were formed: the mNH₄NO₃ · n(KNO₃ · 2 NH₄NO₃) solid solution with the gap of miscibility and the kKNO₃ · l(KNO₃ · 2 NH₄NO₃) solid solution with one-sided limited miscibility.     

Effect of the relative content of Y,Ba, and Cu on the superconducting transition characteristics of the Y?Ba?Cu?O System

By varying the content ratio of the initial products, nine compounds of the Y Ba Cu O system have been produced. These were studied to find their T_c values, critical currents j_c at 77 K and effects of compression stress on the U(j)-curves. Mechanical loading has been found to result in a shift of the U(j)-curve towards a larger current. A correlation between the critical current value, the slope of the U(j)-curve, and the stress induced shift is shown to exist. Samples with equal absolute deviations from the stoichiometric composition reveal close properties, the better the smaller is the deviation.     

Resistance and Current Density Studies on Plasma Sprayed Coatings of Bi(Pb)?Ca?Sr?Cu?O Superconducting Materials

Plasma spraying is a potential technique for forming flexible tapes from brittle high T_c oxides. It is possible to obtain superconducting Bi(Pb) Ca Sr Cu O coating by suitable heat treatment schedule after spraying. In an effort to get maximum transport current densities (J_c) of the coating, the content of lead and sintering time have been optimised. A J_c value of 200 Amp/cm² is obtained in Bi_1.4Pb_0.6 · Ca₂Sr_1.9Cu₃O_y specimen coated on silver sprayed Fe[(Ag)/Fe] substrate. Remarkable improvement in J_c values up to 694 Amp/cm² is obtained in the same specimen coated on Ca₂Sr_1.9Cu₃O_y sprayed Fe[Ca₂Sr_1.9Cu₃O_y)/Fe] substrate. The observed decrease in J_c(B) curves with increase in magnetic field shows the presence of weak coupling between the grains.     

Stabilization of the melt composition in Ga?Al?Sb?As

In this work we present a new effect of stabilization of the Ga Al Sb As melt composition when it is in contact with the GaAs substrate. It was found that the As content in the Ga Al Sb As melt did not depend on the initial Sb concentration when the liquid phase was formed by saturating the Ga Al Sb melt from the GaAs substrate. This effect is supposed to be due to the change in phase equilibria conditions caused by large lattice mismatch between the substrate and the solid in equilibrium with the liquid.