Screening Effects in High Resistivity CdTe for X-ray and Gamma Ray Detectors

Abstract

The possibility to estimate an upper limit of concentrations of defects forming deep levels in high-resistivity CdTe is discussed based on evaluation of room-temperature photocurrent spectra. A model explaining the shift of the maximum of photocurrent with the applied electric field as a consequence of screening effects caused by space charge accumulated on deep levels is presented. Theoretical calculations show that a maximum concentration of deep levels leading to the observed shift of the photocurrent maximum is less than ∼1013 cm−3 for typical capture cross sections of electrons and holes. This result supports the models assuming formation of a high-resistivity state with a minimum deep level doping.