Method to Distinguish Between Buffer and Surface Trapping in Stressed Normally-ON GaN GITs Using the Gate-Voltage Dependence of Recovery Time Constants

Drain current recovery transients are analyzed in normally-ON (NON) gate injection transistors (GITs) subjected to different kinds of stress. The recovery is measured as a function of forward gate bias, ${V}_{\text {G}}$ , which controls the number of holes injected from the gate and speeds up the recovery. Unlike conventional normally-OFF GITs, the newly designed NON GIT test structures allow simple characterization of buffer trapping during back-gating. By comparing the ${V}_{\text {G}}$ -dependence of recovery time constants for OFF-state and semi- ON state stress with those obtained from back-gating experiments we are able to distinguish between buffer and surface trapping. Our approach is simple and does not require time-consuming temperature-dependent measurements. It is found that OFF-state stress causes negative charge accumulation in the buffer, while semi- ON state stress leads to accumulation in both, buffer and surface. The use of NON GITs enables to measure the recovery time constants related to the buffer over a wide span of six orders of magnitude ( $10^{-{4}}$ –100 s).