Influence of carrier diffusion on the intrinsic response time of semiconductor avalanches

The intrinsic response time τi of semiconductor avalanches has been determined from microwave measurements on Si, Ge, and GaAs IMPATT diodes of various structures (n+-p, p+-n, Schottky barrier). A theory has been developed to calculate τi for these diodes. It was found that the effect of carrier diffusion has to be taken into account to remove a systematic discrepancy between experimental and theoretical values of τi. For Si the value of the average high-field diffusion constant D̄=80 cm2/sec for E=400 kV/cm, taken from the literature, could be used satisfactorily. For Ge and GaAs, where no information on D̄ is available, D̄=100 cm2/sec for E=200 kV/cm and D̄=250 cm2/sec for E=400 kV/cm, respectively, had to be chosen to explain the experimental values of τi.