A Monte Carlo method has been developed for the study of electron transport properties in ZnO MESFET for high field, using a five-valley conduction band model. The effects of upper valleys on the characteristics of ZnO MESFETs have been investigated. The following scattering mechanisms, that is impurity, polar optical phonon, acoustic phonon, alloy and piezoelectric are included in the calculation. Ionized impurity scattering has been treated beyond the born approximation using the phase-shift analysis. The simulation results show that on the drain side of the gate region, hot electrons attained enough energy to be scattered into the upper satellite conduction valleys. Approximately 17% of the electrons occupy the higher valleys (mainly U and M valley). The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible, and the predicted drain current and other electrical characteristics for the simulated device including upper valleys show much closer agreement with the available experimental data.

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