Field and temperature dependencies of the quantum efficiency of GaAs and GaP Schottky diodes

An experimental and theoretical study of GaAs and GaP Schottky photodiode q uantum efficiency is reported. The quantum efficiency was investigated as a function of temperature in the 80-360 K interval and as a function of elec tric field in the space-charge region in the 15-50 kV cm(-1) interval. The photocurrent is found to increase strongly with temperature, by a factor of three for GaP diodes and by a factor of six for GaAs diodes. We believe th at this is evidence of a high concentration of imperfections in the space-c harge region. These imperfections manifest themselves only in photoelectric properties. Such defects act as traps and capture both photoelectrons and photoholes. At low temperatures, most of the pairs recombine, but some frac tion of them escape from the traps due to thermal excitation and give an el ectric current which rises with temperature. The time of the capture has to be of the order of the carrier drift time, 10(-11) s. The electric field d ependence of the quantum efficiency is also evidence of the high trap conce ntration. We believe that this is due to a field-induced shift of the carri er energy level in the trap. At high temperature, the photon energy and ele ctric field dependencies of the photocurrent tend towards saturation.