K. W. Benz

Compensation of CdTe by Doping With Gallium

Semi-insulating CdTe single crystals doped with Ga were grown from the vapour phase by the modified Markov technique MMT. The study of the resistivity map in the cross-sections cut along the growth direction has been performed. The compensation phenomenon is analysed in the framework of the three levels Fermi-statistic model. It is shown that a semi-insulation behaviour throughout the ingot is due to the compensation of shallow impurities by the deep level. From the low-temperature photoluminescence spectra it was concluded that shallow donors (Ga Cd ) are partly compensated by (Ga Cd -V Cd ) - and (Ga Cd -Cd Te ) complexes and by residual acceptors (Na Cd , Cu Cd ). The microscopic structure of (Ga Cd -Cd Te ) complex is proposed based on the value of its local phonon mode and the growth conditions. A native defect like Teed which has a deep level near the middle-band-gap is suppose to give a stable compensation and a tolerance for variation in shallow impurity concentrations.

P–T–X phase equilibrium studies in Zn–Te for crystal growth by the Markov method

Abstract Synchrotron topography characterization of vapor grown ZnTe crystals showed that the available data in this system are not sufficient to control the growth parameters. First P – T – X phase equilibrium studies confirm that the stoichiometric plane X =50 at.% Te is completely outside of the single-phase volume of ZnTe. The Te boundary exhibits retrograde solubility. The maximum Te non-stoichiometry of 0.0186 at.% was found at T =1344 K.

P–T–X Phase Equilibrium in the Zn–Te System

P-T-X data are the thermodynamic basis for modeling the crystal growth of materials with controlled stoichiometry. In this paper results of the first direct experimental measurement of the total vapor pressure are reported for three-phase equilibria SLV (solid-liquid-vapor) and VLS (vapor-liquid-solid) in Zn-Te, and the P-T projection of the P-T-X phase diagram is constructed. Geometrical analysis of the phase equilibrium showed that three congruent processes are observed in the Zn-Te system: congruent melting (S = L), sublimation (S = V), and vaporization (L = V). All three congruent curves are tangent to SLV. Consequently, all three congruent points are on the Te-side of the maximum melting point of ZnTe. The vapor pressure scanning method was applied to determine the maximum non-stoichiometry as a function of the temperature. The solidus volume of ZnTe was shown to be on the Te-side of the stoichiometric plane.

Defect engineering in CdTe, based on the total energies of elementary defects

This paper presents data on experimentally and theoretically deduced total energies and energy level positions in the band-gap for eight elementary defects in CdTe. Based on these data, the total energy dependence on the Fermi-level position in the band-gap is graphically analysed. Two types of defect reactions, which are responsible for cadmium vacancy (VCd) creation and transformation, are discussed. It is shown that the most probable candidate for the native deep-level donor is a tellurium antisite.

Transmission Electron Microscopy Study of CuIn3Se5

The off-stoichiometric In-rich phase CuIn 3 Se 5 was studied by means of electron diffraction and high resolution electron microscopy. The structural investigations provide unambigouesly a tetragonal structure of this compound which can be derived from the chalcopyrite structure of CuInSe 2 . A theoretical model with an ordered occupation of vacancies is discussed for this structure. A detailed comparison between the theoretical model and the experimental archieved ones is revealed.

Correlation of resistivity with zinc content in a vapor grown (Cd, Zn)Te:Se

We report the possibility to grow semi-insulating (Cd,Zn)Te:Se crystals by the modified Markov method (MMM) from the vapor phase. When oriented Cd(Te,Se) seed material was used for the growth, lattice matching and doping with Se resulted in an increase of resistivity up to several units of 109 Ω cm. A homogenous Zn distribution was also observed. The content of Se and Zn in the seed and grown crystals was determined by photoluminescence and energy dispersive analysis by x ray measurements. Resistivity and Zn concentration maps show a good spatial correlation in which the highest values of resistivity correspond to the areas of the highest Zn concentration. The main part of the crystals demonstrate a low extinction coefficient in the IR spectral region, except for the Zn inhomogeneity region.

Transmission Electron Microscopical Studies of the Layered Structure of the Ternary Semiconductor CuIn5Se8

The structure of the off-stoichiometric In-rich ternary phase CuIn 5 Se 8 was studied by means of electron diffraction and high-resolution electron microscopy. The compound shows a layered structure with a 7-layer stacking sequence of closed-packed planes, which contains both cubic and hexagonal stacking of Se atoms. The studied CuIn 5 Se x bulk crystal is known as the β-phase of this compound.

Characterization of CdTe:Zn:V crystals grown under microgravity conditions

CdTe:Zn:V crystals grown by the seeded Bridgman method in microgravity conditions during the STS95-Spacelab-AGHF-1 mission and in the ground laboratory (l-g) were analyzed and compared. The results obtained clearly show that the structural quality of the space crystal is better. Density of inclusions, concentration of dislocations, and presence of stresses are lower in the microgravity-grown (μ-g) crystal. The l-g crystal contains twins and grains from the beginning of the growth process, that is, from the near-seed region. In general, the concentration of inclusions and amount of segregated impurities on the l-g crystal are larger than in the μ-g crystal. X-ray rocking curves and low-temperature photoluminescence spectra demonstrate the relatively high quality of both crystals on a microscale at the beginning of the growth and show that the l-g conditions were worse at the end. The results of this investigation demonstrate a positive role of contactless growth and μ-g conditions in the melt in suppressing the creation of inclusions and dislocations.