Channel resistance behavior of GaN HEMTs: an experimental study

The commercial availability of gallium nitride high electron mobility transistors (GaN HEMTs) has increased over the last few years. However, current collapse phenomenon, in which the channel resistance temporarily increases after high voltage switching stress, remains an issue. The phenomenon has been studied on a submicrosecond timescale, but on a longer timescale the channel resistance behavior is mostly unidentified. In this paper, the channel resistance behavior of GaN HEMTs is studied after different switching stresses. The main findings are that the channel resistance is higher after switching stress, but recovers to its prestress value during a rest period of minutes. The stress time is the decisive factor in the channel resistance behavior; longer stress times increase the channel resistance and the recovery time. Very low switching frequencies, such as 50 Hz, further boost the phenomena, but with higher switching frequencies the difference in channel resistance between different frequencies is negligible.