Comparison between wurtzite phase and zincblende phase GaN MESFET's using a full band Monte Carlo simulation

Cutoff frequency, breakdown, voltage, and the transconductance of wurtzite and zincblende phase GaN MESFET's have been calculated using a self-consist ent, full band Monte Carlo simulation. The effect of interface states on th e device performance is modeled by including uniformly depleted regions at the del ice surface under the passivation layers, It is found that the drai n current increases gradually with increasing drain-source voltage at the o nset of breakdown for both phases. The calculated breakdown voltage for the wurtzite device is considerably higher than the breakdown voltage calculat ed for the zincblende device, On the other hand, the zincblende device is c alculated to have higher transconductance and cutoff frequency than the wur tzite device. The higher breakdown voltage of the wurtzite phase device is attributed to the higher density of electronic states for this phase compar ed to the zincblende phase. The higher cutoff frequency and transconductanc e 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 mu m gate-length zincblende GaN MESFET are calculated to be 220 GHz and 210 mS/mm, respecti vely. The corresponding quantities for the wurtzite GaN device are calculat ed to be 160 GHz and 158 mS/mm.