Quantitative Elektronenstrahlmikroanalyse und Zyklotronresonanzmessungen an Wismut-Antimon (Bi1−xSbx)

For the investigation of the electronic properties of bismuth-antimony single crystals the analysis of their chemical composition is important. For this te Electron Microprobe Analysis is a suitable method. In general the quantitative Elektron Microprobe Analysis requires to take into account various influences. This is possible by correcting calculations on the basis of theoretical models. For the reproducibility and the comparability of analytical results information is necessary on conditions of measurement and on theoretical corrections. In this paper an investigation is made, under which conditions in the analysis of bismuth-rich bismuth-antimony alloys the correction can be neglected. The successful utilization of the Electron Microprobe Analysis for the investigation of the dependence of the band structure of Bi_1−xSb_x on the antimony concentration x is shown by the example of the measurements of cyclotron resonance.     

Influence of Bi1−xSbx and Sb overlayers on the annealing behaviour of Ag films

Annealing of thin Ag films covered by Bi_1−xSb_x (x = 0.09) and Sb overlayers, respectively, has been investigated by measuring the electrical resistance. Material exchange by diffusion leading to the formation of an intermetallic phase between Ag and Sb was found to be mainly responsible for the annealing effects. By X-ray and electron diffraction the intermetallic compound has been identified as the ε-phase Ag₃Sb. The diffusion processes due to annealing were studied by SIMS. A correlation between the measured resistance and electron micrographs of the cross-sectional film structure was found.     

Lattice Parameter Study in the Bi1–xSbx Solid-solution System

The lattice parameters of Bi_1–xSb_x single crystals were measured for 0 ≦ x ≦ 1 by a special X-ray diffractometer technique using reflections chosen so that minimum errors were achieved. Corrections for thermal expansion and refraction were applied. The antimony concentration was determined by means of electron microprobe analysis. The dependences of the lattice parameters on x (in nm) can be described with good approximation by a = 0.45469 – 0.02398x and c = 1.186294 – 0.058632 [1 + 1.26 (x⁻¹ – 1)]⁻¹, resp. The behaviour of the parameter a is in agreement with the earlier study by CUCKA and BARRETT , whereas their linear expression for c(x) (0 ≦ x ≦ 0.3) was not confirmed.     

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.     

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).     

Results of crystal growth of bismuth-antimony alloys (Bi100–xSbx) in a microgravity environment

Results of two experiments are presented for growth of crystals from (Bi_100–xSb_x) alloys in a microgravity environment. In the growth experiments different variants of the Bridgman technique were used. It was shown that in crystal growth from the melt in closed ampoules under microgravity conditions convection can be prevented completely. Therefore it is possible to grow crystals from melts of some components under diffusion controlled conditions of mass transfer. In microgravity a reduced interaction between the melt and the confining walls was observed even if they have large contact with each other. The investigation of surface morphology corroborated the importance of surface effects for crystal growth from the melt under microgravity conditions. Measurements of electronic properties of crystals grown in microgravity showed a good quality in comparison to earth grown crystals. Because under microgravity conditions in closed ampoules the diffusion controlled mass transfer can be realized and the interaction between the melt and confining wall is reduced, homogeneous crystals with high perfection can be grown melts of some components.     

Thick LPE Layers of InAs1—xSbx for 3—5 μm Optoelectronic Applications

N-InAs_1—xSb_x/n, p-InAs heterostructures were grown by liquid phase epitaxy on (100) oriented substrates. The layer composition was varied in the interval 0 < x < 0.1, the corresponding lattice mismatch being not greater than 0.5%. The layer composition was studied by microprobe analysis on the surface of the structure cross-section. Microhardness profiles were investigated using Vickers and Knoop indentors. Raman scattering was also studied.     

Electron-beam microprobe analysis of epitaxial GaxIn1−xP solid solutions

Ga_xIn_1–xP epitaxial layers were investigated by means of a scanning electron microscope X-ray microanalyser. The conditions for quantitative X-ray microprobe analysis are discussed. The growth of Ga_xIn_1–xP layers is possible on GaP substrates with x > 0,8 and on GaAs with 0,3 < x < 0,6. For the deposition of layers with 0,5 < x < 0,8 two substrate materials are possible: GaAs_1–xP_x or Ga_xIn_1–xP with suitable compositions. These materials must be epitaxially deposited by step by step layer growth or by vapour phase epitaxy, respectively.     

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.     

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.     

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.     

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.     

Quantitative Bestimmung der Zusammensetzung von Ga1−xAlxAs-Epitaxieschichten mit der Elektronenstrahl-Mikroanalyse (ESMA)

Several methods of correcting the X-ray intensity in the electron probe microanalysis were examined for getting the local concentrations of Ga, Al and As in Ga_1−xAl_xAs epitaxial layers. Most correct results were obtained by combining the method of BIRKS for the Al-determination with that of DUNCUMB /REED /SPRINGER for the Ga-determination. In this case the mean departure from 50% for the sum of the Ga and Al atom-percents is only −0.1%. Equations for the mutual conversion of concentrations into masses, necessary for the practical use, are given in an appendix.     

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.     

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.     

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.     

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.