Monte Carlo simulation of high field electron transport in ZnS

Abstract

An ensemble Monte Carlo simulation of high field transport in ZnS has been developed. The model includes a nonparabolic three valley model of the first conduction band and a single valley in the second conduction band. The density of states for the first conduction band was modeled phenomenologically to resemble the density of states obtained by numerical pseudopotential calculations. This density of states was used only in the calculation of the scattering probabilities and no attempt was made to modify the conductivity effective mass to conform to the band structure at higher energies. The fourth valley in the conduction band is included even though not much is known about the band parameters associated with it. In our first approximation, we treat it as a valley similar to the X valley of the first conduction band, with similar effective mass, deformation potentials, etc. This assumption is not much different from what has been done in previous Monte Carlo treatments. The simulation includes scattering mechanisms associated with acoustic, intervalley and polar optical phonons, as well as ionized impurity scattering and impact ionization. The inclusion of the second conduction band is found to have a significant impact on the energy distribution at fields above 1 MV/cm. The second conduction band is also important because of its effect on the impact ionization rate, which has been calculated. Other results such as drift velocity and average electron energy are presented and are found not to differ much from the results of previous investigations.