A detailed characterization of the transient electron transport within zinc oxide, gallium nitride, and gallium arsenide

Abstract

A three-valley Monte Carlo simulation approach is used in order to probe the transient electron transport that occurs within bulk wurtzite zinc oxide, bulk wurtzite gallium nitride, and bulk zinc-blende gallium arsenide. For the purposes of this analysis, we follow the approach of O'Leary et al. [O'Leary et al., Solid State Commun. 150, 2182 (2010)], and study how electrons, initially in thermal equilibrium, respond to the sudden application of a constant applied electric field. Through a determination of the dependence of the transient electron drift velocity on both the time elapsed since the onset of the applied electric field and the applied electric field strength, a complete characterization of the transient electron transport response of these materials is obtained. We then apply these results in order to estimate how the optimal cut-off frequency and the corresponding operating device voltage vary with the device length. We find that while the cut-off frequency found for the case of zinc-blende gallium arsenide, 637 GHz for a device length of 100 nm, is marginally less than that found for the cases of wurtzite zinc oxide and wurtzite gallium nitride, 1.05 and 1.32 THz, respectively, the corresponding operating voltage found for the case of zinc-blende GaAs, 0.08 V, precludes the use of this material for the operation of devices in the terahertz frequency range if higher powers are required; the corresponding operating voltages for the cases of wurtzite ZnO and wurtzite GaN are found to be 8 and 4 V, respectively. These results clearly demonstrate the compelling advantage offered by wurtzite zinc oxide and wurtzite gallium nitride, as opposed to zinc-blende gallium arsenide, for electron devices operating in the terahertz frequency range if higher powers are required.