A model for impact ionisation in wide-gap semiconductors

Publisher Website
Google Scholar
Abstract
Mean free paths associated with the scattering of electrons and holes are derived from experiments on impact ionisation in wide-gap semiconductors using the lucky-drift model. It is found that the mean free path for an electron or hole in any semiconductor obeys a simple universal law which implies a common phonon energy for electron and hole scattering and a dependence of mean free path on threshold energy ( lambda varies as Ei-12/). The latter dependence is plausible in terms of a simple view of scattering of high-energy carriers in a nonparabolic band. This universal model is derived on the basis of experimental data reported by various authors in Si, Ge, GaAs, and InP. Results for GaSb and its alloys appear to be anomalous, whereas data from GaInAs in InGaAsP tend to support the model. The model predicts the ratio of ionisation coefficients k= beta / alpha and its dependence on field and temperature. It is shown that k in any semiconductor is determined by only the ratio of threshold energies of electrons and holes. A comparison with reported values is made and brief discussions of the spin-orbit resonance effect in AlGaSb and of the enhancement in GaAs/AlGaAs multilayers are given.