Off State Breakdown in GaAs Power HFETs

This work brings new experimental data shedding light on the still controversial issue of o-state breakdown in microwave power FETs, which limits the power handling ca- pability. By means of measurements per- formed on AlGaAs/GaAs power HFETs in a wide range of temperatures, we show that: 1) At relatively low drain-gate voltage, the gate current comes from thermionic-eld emission. 2) As we approach o-state breakdown, im- pact ionization of electrons accelerated by the large drain-gate eld becomes the dominant mechanism originating the gate current. 3) For even higher values of the drain-gate volt age, both electrons and holes possibly ionize, and the drain-gate diode avalanches. Our experimental ndings diverge in some respects from other published data and rep- resent therefore a new contribution to the un- derstanding of this important issue.