Impact ionization coefficients of electron and hole at very high fields in semiconductors

We have fitted the soft lucky drift model of impact ionization of Ridley to experimental data for GaAs, InP, Si, Ge and (In)(Ga)(As)(0.47)(0.53). Excellent fit of theory to experimental data were obtained by using least square fitting algorithm. A generalized Keldysh formula has been used, due to introduction of a soft threshold factor. Generalized Keldysh formula originates from realistic energy bands of semiconductors at high electric field which reflects the density of states of energy bands. Keldysh factor and a new mean free path are calculated. A comparison with reported values of both Ridley and Marsland showed reasonable agreement in mean free path, but there is still a large difference among Keldysh factors.