[en] The issue of modelling of point defect structure in In(Ga)-doped CdTe crystals has been analyzed. Contrary to previous papers, it has been shown that high-temperature point defect equilibrium modelling can be successfully achieved if sufficient experimental data are available and appropriate calculation methods are used. Room temperature free electron densities were computed for CdTe:In crystals and compared with experimental data. Since the density of point defects changes during cooling from the preparation to operational temperatures, it cannot be estimated. Therefore, a new approach, including calculation of a certain fitting Δ parameter, is proposed. Its determination allows preparation/cooling conditions necessary to prepare material with the desired electric properties to be defined

[en] The melting process of pure CdTe as well as of CdTe+2 mol% Ge and CdTe+2 mol% Sn was investigated experimentally by means of differential thermal analyses. The samples were heated above their respective melting temperatures T_m and annealed at various defined temperatures before continuation of heating. Volume fractions of clusters, remaining in the melt even above the melting point, were derived from the area of the corresponding thermal effects. It was confirmed that the melt consists in all cases of two types of structures: clusters (with a short-range order close to the crystalline substance) within an amorphous matrix. The size of the clusters was estimated from the activation energies of the crystallization process; they were found to consist of about 66 to 98 atoms in pure molten CdTe. For two cases, pure CdTe and CdTe+2 mol% Ge, 'hot crystallization' was observed, i.e. after a given heat treatment the melt crystallized at temperatures above T_m

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[en] The electrical properties of CdTe:Pb single crystals at high temperatures (400-900 deg. C) and under controlled Cd vapor pressure (0.001-3 atm) were investigated for the first time. The temperature and baric dependences of the conductivity and Hall coefficient were measured. Low (in comparison with undoped CdTe) electron concentration indicates an increase in the number of impurity point defects related to the Pb impurity. The results obtained are explained within the Kroeger theory of quasi-chemical reactions of defect formation on the assumption that lead may exist in the isolated state (Pb_Cd⁺) and as a component of (Pb_Cd⁺V_Cd^2-)^- associates

[en] High temperature equilibrium in situ in CdTe left angle In right angle single crystals in a wide range of temperature (700-1200 K) and dopant content (6 x 10¹⁶∝10²⁰ at/cm³) was studied. Self-compensation processes, which occur at these conditions, were modelled using quasichemical defect reaction theory. During heating the self-compensation degree passed through a minimum under Cd saturation and increased under Te saturation. The annealing under Te saturation allowed obtaining high resistive material of both conductivity types. The lowest charge carrier density was equal to ∝3 x 10⁹ cm^-3 and the self-compensation degree reached 100%. Point defect structure modelling showed a good agreement for both high temperature equilibrium and quenched state. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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[en] High temperature Hall effect measurements at 570-1070 K under well defined Te vapor pressure in CdTe single crystals grown by THM and Bridgman techniques were made. Both the free carrier density versus Te vapour pressure value and temperature dependencies were studied. At heating up till ∝870 K the hole density was Te vapor pressure independent, but it varied in different samples from 1 x 10¹⁶ to 1 x 10¹⁷ cm^-3. At higher temperatures the conductivity becomes of intrinsic type, turning then into n-type one. A theoretical analysis of native point defects contents at different conditions in the framework of Kroegers quasichemical formalism was performed. It resulted in the impossibility of mutual compensation of native donors and acceptors proposed by different authors. The results were explained assuming the presence of an electrically active foreign point defect - the oxygen interstitial acceptor. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] We have measured the lattice distortion around As (acceptor) and Br (donor) in CdTe with fluorescence detected X-ray absorption spectroscopy. We could experimentally verify the lattice relaxation with a bond length reduction of 8% around the As atom as inferred indirectly from ab initio calculations of the electric field gradient performed with the WIEN97 package in comparison with the measured value in a Perturbed Angular Correlation experiment as recently reported. We have complemented our own calculations of relaxation with WIEN97 with calculations using the FHI96md pseudo-potential program, which allows the use of larger super-cell sizes. Encouraged by the good agreement between experiment and model calculation for As in CdTe as well as similarly for the isovalent Se in CdTe, we extended our investigation to Br in CdTe, where the electric field gradient has also been measured, and could not only verify the derived lattice expansion around Br with our EXAFS analysis but additionally observe fractions of Br in the A-center as well as in a DX-center configuration.

[en] At first the experimental results of detailed Hall effect measurements at high-temperature defect equilibrium under Cd/Te vapor pressure in CdTe single crystals were obtained. They indicate that at these conditions Bi forms in CdTe crystals mainly Bi_Cd donor centers. The analysis of the free electron density temperature dependencies allows to conclude that up to 800 K the electrons of dopant atoms define the sample's electrical properties. The native donor point defects begin to influence the electro-neutrality condition above this temperature. The research of high-temperature electrical properties of Bi-doped CdTe samples shows that the real electrical active Bi content in the investigated crystals is ∝10¹⁷ at/cm³. The electron density dependencies vs P_Cd, modeled at constant temperatures (500-900 C), in the assumption of deep Bi donor (E_V+0.71 eV) are in good agreement with experiment. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)