Electron drift velocity in wurtzite ZnO at high electric fields: Experiment and simulation

The hot-electron effect on electron transport in nominally undoped ZnO epilayers is studied at electric fields up to 430 ± 50 kV/cm applied with 3 ns voltage pulses. The transient measurements do not demonstrate any change in the electron density at the fields up to 320 kV/cm. The deviation from Ohm’s law can be approximated by the linear dependence of the current on the electric field valid at the moderate fields (from 50 to 250 kV/cm). The model calculations based on the Boltzmann kinetic equation are used to demonstrate that the differential mobility at the moderate fields is almost independent of the scattering on the charged point defects. The electron drift velocity is estimated from the experimental values on the differential conductivity and the current density together with the calculated differential mobility as a reference for calibration. The drift velocity reaches 2.7 ± 0.3 × 10 7 cm/s at the field of ∼ 320 kV/cm and approaches the theoretical limit predicted by the known Monte Carlo simulations.