ABSTRACT
A 2-D physical model of the GaAs MESFET based on bipolar transport, thermal heating and impact ionisation has been developed to investigate breakdown phenomena. The effects of both free surface and substrate traps on a number of different device structures have been examined. Trapping in the substrate is found to lower the breakdown voltage by enhancing the local electric field, and can cause soft breakdown behaviour. Surface charge trapping relaxes the local electric field and raises the breakdown voltage.
