Ballistic electron impact ionization in GaAs and in InP avalanche devices

It is shown that electrons have a high probability Pth of ballistically gaining the ionization threshold energy when a high electric field E(>4×10⁵V/cm) is applied along certain crystal orientations in GaAs and InP avalanche devices. In GaAs we find Pth() < Pth(), whereas in InP the opposite occurs indicating a strong band structure dependence of the ionization process and of ballistic transport. The electron ionization rates calculated from our ballistic model do not contain any adjustable parameter and are in good agreement with experimental data in GaAs.