THE GATE-BIAS DEPENDENCY OF BREAKDOWN LOCATION IN GAAS METAL-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS (MESFETS)

The breakdown behaviour of refractory metal self-aligned GaAs metal semiconductor field effect transistors (MESFETs) has been studied by two-dimensional simulation using a drift-diffusion transport model and emission microscopy. Exact quantitative simulation of the device characteristics has been achieved for a device with a four fold implant scheme. The location of breakdown, as defined as the area of high avalanche generation rate, has been found to have a specific gate bias dependence: For open channel bias condition (V(gs) = 0 V) impact ionization is initiated at the n+ to channel implant interface, under subthreshold conditions however at the gate contact edges. The shift of the location as well as the MESFET specific gate bias dependence of drain breakdown could be explained by careful examination of the electric fields and the currents (holes and electrons) involved. These results have been experimentally verified by the light emission of the devices which were measured by high resolution emission microscopy.