SYMPTOMS OF STRESS-INDUCED GAIN DEGRADATION IN POWER MESFETS

GaAs metal-semiconductor field effect transistors configured as microw ave power amplifiers have been observed to degrade under normal device operations at high gate-to-drain fields. The nature of this degradati on is an increase in the gate current, with a subsequent decrease in t he gain. We present evidence that crystallographic defects in the acti ve region are responsible for this ''power slump'' and that these defe cts originate during device operation due to the high strain fields wh ich exist as the result of passivation layer processing. Strain data a nd x-ray topographic images support our assertion that passivation lay er processing induces high strain in and around the gate-to-drain regi on of the device. Topographic images show that an increase in dislocat ion density occurs in the highly stressed regions after power slump. B y varying deposition parameters, we can produce passivation films, whi ch induce less stress in the active region, resulting in less dislocat ion generation and a less severe power slump.