HIGH-POWER HIGH-EFFICIENCY X-BAND ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS WITH UNDERCUT COLLECTORS/

We report on the power performance of X-band AlGaAs/GaAs heterojunctio n bipolar transistors with undercut collectors for reduced base-collec tor capacitance, A 10 x (2.8 x 50) mu m(2) HBT unit cell exhibited 2,0 9-W continuous wave (CW) output power (4,18-W/mm power density), 62.2% power-added efficiency, and 7,13-dB associated gain at 10 GHz at a co llector bias voltage of 10 V, When tuned for maximum efficiency, the s ame transistor delivered a CW output power of 1.36 W, a power-added ef ficiency of 74.2%, and an associated gain of 7.32 dB at the same frequ ency and collector bias voltage, To our knowledge, this is the first d emonstration of high-power (>1,3 W), high-efficiency (>74%) AlGaAs/GaA s HBT's using a simple collector undercut technique without the need f or significant modifications of baseline HBT process.