GaN transistor reliability and instabilities

Abstract

GaN based transistors are vulnerable to long time period instabilities as a result of the wide bandgap. In this paper we review the effect of the bulk GaN dopants, which are added to ensure a highly resistive buffer, on the current-collapse which occurs on switching from the off-state to the on-state. The iron doping frequently used in RF devices leads to a trap level in the upper half of the gap which generates a small, reproducible, and straightforwardly modelled current-collapse. On the other hand the carbon doping used in many power devices results in current-collapse which can be large but is strongly impacted by the presence of leaky threading dislocations. A powerful technique to characterise the buffer and extract the vertical leakage in the different layers within a GaN-n-Si power HEMT based on ramping the substrate bias is introduced.