Comparison between wurtzite phase and zincblende phase GaN MESFETsusing a full band Monte Carlo simulation

Cutoff frequency, breakdown voltage, and the transconductance of wurtzite and zincblende phase GaN MESFETs have been calculated using a self-consistent, full band Monte Carlo simulation. The effect of interface states on the device performance is modeled by including uniformly depleted regions at the device surface under the passivation layers. It is found that the drain current increases gradually with increasing drain-source voltage at the onset of breakdown for both phases. The calculated breakdown voltage for the wurtzite device is considerably higher than the breakdown voltage calculated for the zincblende device. On the other hand, the zincblende device is calculated to have higher transconductance and cutoff frequency than the wurtzite device. The higher breakdown voltage of the wurtzite phase device is attributed to the higher density of electronic states for this phase compared to the zincblende phase. The higher cutoff frequency and transconductance of the zincblende phase device is apparently due to the greater electron velocity overshoot for this phase compared to that for the wurtzite phase. The maximum cutoff frequency and transconductance of a 0.1 μm gate-length zincblende GaN MESFET are calculated to be 220 GHz and 210 mS/mm, respectively. The corresponding quantities for the wurtzite GaN device are calculated to be 160 GHz and 158 mS/mm