Symptoms of stress-induced gain degradation in power MESFETs

Abstract

GaAs metal-semiconductor field effect transistors configured as microwave power amplifiers have been observed to degrade under normal device operations at high gate-to-drain fields. The nature of this degradation is an increase in the gate current, with a subsequent decrease in the gain. We present evidence that crystallographic defects in the active region are responsible for this “power slump” and that these defects originate during device operation due to the high strain fields which exist as the result of passivation layer processing. Strain data and x-ray topographic images support our assertion that passivation layer processing induces high strain in and around the gate-to-drain region of the device. Topographic images show that an increase in dislocation density occurs in the highly stressed regions after power slump. By varying deposition parameters, we can produce passivation films, which induce less stress in the active region, resulting in less dislocation generation and a less severe power slump.