Low-temperature characteristics of electron ionization rates in (100)- and (111)-oriented InP

Electron ionization rates α in both (100)- and (111)-oriented InP have been derived at a low-temperature range between 77 and 293 K from photomultiplication data measured on a mesa-type (100)-oriented InP diode and a planar type (111)-oriented InP diode. It has been found that there is no difference in α between the two orientations in this temperature range. This indicates that the contribution of ballistic electrons to impact ionization is insignificant not only at room temperature but at low temperatures. A Monte Carlo simulation of α in both (100)- and (111)-oriented InP at low temperatures have been carried out for the analysis of the experimental data. The simulated results have been found to agree with the experimental ones fairly well in the considered electric field and temperature ranges. α has been demonstrated to have no orientation dependence and the probability of ballistic electrons to cause impact ionization has been found to be extremely small (about 0.01% at 300 K and 0.05% even at 77 K). No anisotropy in electron ionization rates in InP has been attributed to this very small probability.