Diminution of impact ionization rate of charge carriers in semiconductors due to acoustic phonon scattering

Abstract

The effects of acoustic phonon scattering on the impact ionization rate of charge carriers in a semiconductor have been studied in this paper. The inelastic interactions of charge carriers with both deformation and piezoelectric acoustic phonons have been considered. An analytical expression of impact ionization rate has been developed by considering all possible types of inelastic collision mechanisms such as acoustic phonon scattering, optical phonon scattering, and inter-carrier scattering prior to the ionizing collision. The said expression has been used to calculate the impact ionization rate of electrons and holes in 4H-SiC as functions of electric field and doping concentration at room temperature. Numerical results show that the ionization rate of charge carriers deteriorates significantly due to the interactions of those with acoustic phonons. This deterioration is found to be more pronounced in hot carriers. The numerical results calculated from the present model have been compared with the ionization rate data calculated numerically using an earlier developed analytical expression of ionization rates, which does not take into account the acoustic phonon-scattering events. The calculated results have also been compared with earlier reported experimental data. It is observed that the numerical results obtained from the present model are in better agreement with the experimental results.