Monte Carlo simulation of impact ionisation in MESFETs

The authors investigate breakdown in a small 1.2 mu m MESFET by means of Monte Carlo simulation. Ionisation in devices operating near pinch off were found to occur in accordance with the nominal gate-drain electric field but at lower gate reverse bias, the device was vulnerable to oscillating electric fields associated with the formation of accumulation layers. These fields caused significant impact ionisation to occur at relatively low nominal gate-drain potentials. Indeed, the newly formed holes could have a positive feedback effect on the potential causing, the oscillations to increase and the device to eventually breakdown.