K.W. Benz

Defect structure of Ge-doped CdTe

A complex investigation of defect structure of high-resistivity Ge-doped CdTe by a number of optical, photoelectrical and electrical methods was performed. It was found that material properties are strongly influenced by the presence of centers of strong recombination (S-centers) and photosensitivity (R-centers). A model of energy levels dominating the recombination processes in the material was elaborated, where the role of Ge, Fe and Cu related as well as native defects (Cd vacancy) is discussed.

White beam X-ray topography at the synchrotron light source ANKA, Research Centre Karlsruhe

At the new synchrotron light source ANKA (Angstrom Karlsruhe, Germany) one beamline is optimised for white beam synchrotron topography. First topographs taken at various geometries and materials demonstrate the easy operation and the high resolution. Details about the experimental set-up are given. Large area and section topography in transmission allow a quantitative analysis of the type of dislocations and the dislocation density up to 106 cm−2 which is shown for GaSb:Te and InP:S, respectively. For highly absorbing materials like CdTe the back reflection geometry is adequate to analyse dislocation networks, twins and small angle grain boundaries. The grazing incidence method is used for the characterisation of strain and defects as a function of depth by varying the tilt of the sample which is helpful for processed devices like CdTe strip detectors for X-rays.

Thermodynamic Properties of ZnTe in the Temperature Range 15–925 K

The heat capacity of ZnTe was measured in an adiabatic calorimeter in the temperature range from 15 to 330 K and by DSC at T = 290-925 K. The following standard thermodynamic properties of ZnTe were derived: C 0 p (298.15 K) = (49.52 ± 0.10) J K -1 mol -1 ; S 0 (298.15 K) = (81.94 ± 0.17) J K -1 mol -1 ; H 0 (298.15 K) - H 0 (0 K) = (10.98 ± 0.02) kJ mol -1 ; Φ 0 (298.15 K) = (45.12 ± 0.10) J K -1 mol -1 , Temperature dependences of the heat capacity and the Gibbs free energy function are derived for the temperature range up to 1500 K. The Debye temperature calculated from the specific heat data is Θ D = 252 K.

Identification of Cl and Na Impurities in Inclusions of a Vapor-grown CdTe Doped with Zn and Cl

Morphology and analysis of composition of inclusions were done by secondary electron microscopy and spatially resolved energy-dispersive analysis of x-ray on semiintrinsic CdTe:Cl and CdTe:Zn:Cl crystals grown from the vapor phase by the modified Markov technique and on undoped CdTe crystals grown from the melt by the Bridgman method. In CdTe:Cl and CdTe:Zn:Cl crystals nonstoichiometric inclusions of about 10-20 μm were found, which contain high concentrations of Cl and Na impurities. The Cl is concentrated in small precipitates of 1-2 μm inside these inclusions. After short-time low-temperature annealing (600 °C), the inclusions mostly disappeared.

Determination of the EL2 introduction rate and Fermi-level shift due to proton and pion irradiation in semi-insulating GaAs

Abstract The bulk damage (namely the introduction rate of the arsenic antisite AsGa and its ionisation ratio, the Fermi-level position and resistivity) was determined as a function of the non-ionising energy loss (NIEL) of hadrons in semi-insulating (SI) GaAs. The study was performed using near-infrared (NIR) absorption and time dependent charge measurements (TDCM) on 23 GeV proton and 192 MeV pion irradiated Liquid Encapsulated Czochralski (LEC) grown GaAs. We have shown that the bulk damage scales linearly with the total NIEL up to a pion fluence of 5 × 1014 particles/cm2. The EL2 introduction rate for the high energetic pions and protons were determined to be 92.7 ± 2.6 cm−1 and 68.1 ± 3.7 cm−1, respectively. A comparison of these values gives a hardness factor for the 192 MeV pions of 9.5 ± 1.4. In addition it was found that the variation of the Fermi-level and resistivity with radiation damage is a function of the initial resistivity of the SI GaAs before irradiation.

CdZnTe:Cl Crystals for X-Ray Computer Tomography Detectors

Processes of growth of semi-insulating Cd 1-x Zn x Te:Cl crystals (x = 0.0002 and 0.1) of n-type conductivity are investigated. From the grown crystals detectors for X-ray computer tomography with small value of photocurrent memory (afterglow) (0.1-0.3%) are obtained.