Microwave power GaAs MISFET's with undoped AlGaAs as an insulator

A metal-insulator-semiconductor field-effect transistor using an undoped AlGaAs layer as an insulator has been fabricated and RF tested. Due to the higher breakdown field of the wide-band-gap AlGaAs, the gate breakdown voltage has been greatly improved as compared with a conventional GaAs MESFET. The prebreakdown gate leakage current of this new device structure is also much lower than that of the MESFET. The presence of the gate insulator also reduces the gate capacitance. All these factors result in a GaAs power FET structure with potentials for high power, efficiency, and frequency of operation. An unoptimized 750-µm gate-width device achieved an output power of 630 mW with 7-dB gain and 37-percent power-added efficiency at 10 GHz. At reduced output power levels, power-added efficiency as high as 46-percent was obtained at X-band.