High power GaAlAs/GaAs HBTs for microwave applications

This paper reports the attainment of high microwave output, up to 0.4 W cw at 10 GHz, with GaAlAs/ GaAs heterojunction bipolar transistors. In addition to high power, the HBTs displayed excellent power-added efficiency (4896) and power gain (7 dB). A key factor in obtaining these high powers and efficiencies is the ability to support high collector-emitter voltages without breakdown. Breakdown voltage was up to 23 V (BVcbo) in the devices reported here. The experimental data are in good agreement with a theoretical model of I-V characteristics near breakdown. The cutoff frequency ftwas found to vary with Vceas expected for electron-drift at a saturation veloclty of 1 × 10⁷cm/s across the base-collector depletion region.