Evaluation of Concentration of Deep Levels from Photoelectric Measurements in Wide Gap High-Resistivity Semiconductors

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 and lux‐ampere characteristics. A model explaining the shift of the maxima of photocurrent and the sublinear dependence of lux‐ampere characteristics in non‐homogeneously illuminated samples with the applied electric field as a consequence of screening effects caused by space charge accumulated on deep levels is presented Numerical solution of drift‐diffusion and Poisson equations shows, that maximum concentration of deep levels leading to the experimentally observed shift of the photocurrent maximum and to the measured sublinear slope of lux‐ampere characteristics is less than ∼1013cm−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.