Breakdown of overlapping-gate GaAs MESFETs

Gate-breakdown mechanisms in GaAs MESFETs have been studied by numerical simulation. The devices simulated include normal passivated and unpassivated MESFETs as well as overlapping-gate MESFETs passivated with low-temperature-grown (LTG) GaAs, normal GaAs, and silicon dioxide. The breakdown voltage is the highest for the overlapping-gate MESFET with LTG GaAs passivation, which agrees with the experimental results reported previously. The high breakdown voltage is the result of an altered electric field near the drain-edge of the Schottky-contact gate. This field modification is achieved most effectively by using an overlapping gate structure. The LTG GaAs is the best passivation layer because of its high resistivity and breakdown-field strength.