Shallow donor impact ionization in n-InP and n-GaAs: influence of doping and compensation

The donor impact-ionization coefficient is calculated using the Boltzmann transport equation. It is shown that impact-ionizing collisions of free electrons with shallow donors induce strong cooling of the hot-electron distribution function. From the obtained results it is found that in the analysis of impurity breakdown or related processes the approach based on phenomenological equations is valid only for small changes of electron concentration. Corresponding graphs for the impact-ionization coefficient are presented for n-InP and n-GaAs.