Theoretical study of direct-current andradio-frequency breakdown in GaN wurtzite- and zinc-blende-phaseMESFETs (metal-semiconductor field-effect transistors)

Abstract

In this paper, we present a comparison of the direct-current (DC)and radio-frequency (RF) breakdown behaviours of representativewurtzite- and zinc-blende-phase GaN MESFET structures based on atheoretical analysis. The calculations are made using afull-band ensemble Monte Carlo simulation that includes a numericalformulation of the impact ionization transition rate. Calculationsof both the DC and RF breakdown voltages are presented for submicronMESFET devices made from either wurtzite- or zinc-blende-phase GaN.The devices are otherwise identical. It is found that the DCbreakdown voltage in the wurtzite-phase GaN MESFET is significantlylarger than that in the zinc-blende-phase device. This is due tothe fact that electron heating occurs more rapidly within thezinc-blende phase than the wurtzite phase of GaN. As a consequence,avalanche breakdown occurs at higher applied field strengths andvoltages in the wurtzite phase than in the zinc-blende phase of GaN.It is further found that the RF breakdown voltage of the devicesincreases with increasing frequency of the applied large-signal RFexcitation.