Degradation of GaAs power MESFET's due to light emission

Investigations were performed on the ability of GaAs power MESFET's to withstand degradation with gate current flows. In forward biasing, no detectable degradation was observed after 4000 hours burn-in test with a current at less than 40 mA/finger. While in reverse biasing, drastic degradation of the devices was observed in several tens of hours with extremely reduced source to gate current flows. It was found that the alien substances were grown in the recessed channels and eroded those channels. This reduces the I
DSS
value to 1/10 of the initial value. Coating the channels with insulating films suppresses the growth of such alien substances and degradation of the devices. The degradation of the devices due to source to gate current is closely related to light emission of the devices.