Bipolar Photo-Hall effect in CdTe

Abstract

Photo-Hall effect and photoconductivity in CdTe were investigated in order to establish a defect model for the explanation of the bipolar character of photoconduction. For our investigation, photosensitive CdTe single crystals have been grown from the melt with excess Te and compensated with CdCl 2. At room temperature the samples were p-type with a dark resistivity of 10 9 Ω cm. Photo-Hall and photoconductivity measurements were performed at several temperatures between 250 and 310 K, and for a large variation of carrier densities by excitation with band gap light. From these measurements, carrier densities p and n were evaluated as a function of the generation rate G. The observed non-linearities in the p( G) or n( G) curves were analysed and explained on the basis of a defect model. This model contains four kinds of defect of Shockley-Read type: One hole trap, two recombination centers and one electron trap. By fitting the theoretical p( G) and n( G) curves to the experimental results energy levels, densities and capture cross sections of the defects could be determined. A good agreement was achieved for all temperatures and generation rates used in the investigation.