Influence of space charge on lux-ampere characteristics of high-resistivity CdTe

The concentrations of defects forming at near-midgap level in high-resistivity CdTe were estimated on the basis of room-temperature lux-ampere characteristics. A simple model explaining their sublinear dependence based on the presence of discrete levels near the midgap is presented. It is shown that accumulation of space charge in the sample can explain the observed experimental data. Theoretical calculations show that a maximum concentration of the midgap level leading to the observed slope alpha of lux-ampere characteristic, I-ph = C X I-alpha, is less than 10(13) cm(-3) for a wide range of capture cross sections of electrons and holes. This result supports models that assume formation of a high-resistivity state with a minimum deep-level doping.