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The internal electric field distribution in cadmium zinc telluride (CdZnTe) X-ray andray detectors strongly affects their performance in terms of charge transport and charge collection properties. In CdZnTe detectors the electric field distribution is sensitively dependant on not only the nature of the metal contacts but also on the working conditions of the devices such as the temperature and the rate of external irradiation. Here we present direct measurements of the electric field profiles in CdZnTe detectors obtained using the Pockel electo-optic effect whilst under in-situ X-ray irradiation. These data are also compared with alpha particle induced current pulses obtained by the transient current technique (TCT), and we discuss the influence of both low temperature and X-ray irradiation on the electric field evolution. Results from these studies reveal strong distortion of the electric field consistent with the build-up of space charge at temperatures below 250K, even in the absence of external irradiation. Also, in the presence of X-ray irradiation levels a significant distortion in the electric field is observed even at room temperature which matches well the predicted theoretical model.

This paper reports on a detailed study of the development of the close space sublimation method, which has been widely used in the preparation of polycrystalline CdTe/CdS solar cells, as an epitaxial method for the growth of thick CdTe single crystal films over 200 lm on GaAs and Ge substrates for highenergy radiation detectors. The resulting microscopic growth phenomena in the process are also discussed in this paper. High-quality single crystalline CdTe thick films were prepared with x-ray rocking curves full width at half maximum (FWHM) values, which were $100 arcsec on Ge substrates and 300 arcsec on GaAs substrates. The quality of thick films on Ge(100) showed a substantial improvement with nucleation in a Te-rich growth environment. No Te inclusions in the CdTe films grown on GaAs(211)B and Ge(100) were observed with IR transmission imaging. Photoluminescence of CdTe/Ge shows a large reduction in the 1.44 eV defect energy bands compared with films grown on GaAs substrates. The film resistivity is on the order of 10 10 X cm, and the film displayed some sensitivity to alpha particles.

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