MONTE-CARLO SIMULATION OF IMPACT IONIZATION 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 elec tric field but at lower gate reverse bias, the device was vulnerable t o oscillating electric fields associated with the formation of accumul ation layers. These fields caused significant impact ionisation to occ ur at relatively low nominal gate-drain potentials. Indeed, the newly formed holes could have a positive feedback effect on the potential ca using, the oscillations to increase and the device to eventually break down.