CHARGE-STATE EFFECTS OF DEEP CENTERS IN SEMICONDUCTORS ON NONRADIATIVE CAPTURE OF CARRIERS BY MULTIPHONON PROCESSES

A set of simplified analytical expressions for carrier capture coeffic ients, including quantatively the charge-dependent effect, have been o btained for easy physical examination and comparison with experiments. The temperature-related charge-state-dependent factor F(T) thus calcu lated could be used to present more accurately the nature and magnitud e of the charge state of a trap centre. The ranges of values of F(T) v alid for attractive, repulsive and neutral centres are also obtained. In addition, we show that the thermal ionization energy for the B cent re in GaAs is a function of temperature. The importance of the data of capture cross-section at low temperatures in determining the charge s tate and characteristic of a deep centre is also manifested. Both the absolute magnitude and the temperature-dependent behaviour of the calc ulated capture cross-section are well-supported by the very good fits to the experimental electron cross-sections for A and B centres in GaA s reported by Lang [7] and Wang et al. [22] and for Cu centre in Ge re ported by Zhdanova and Kalashnikov [23].