ALGAAS/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS WITH REDUCED BASE-COLLECTOR CAPACITANCE FABRICATED USING SELECTIVE METALORGANIC CHEMICAL-VAPOR-DEPOSITION

Selectively grown AlGaAs/GaAs heterojunction bipolar transistor (HBT) with a reduced base-collector capacitance is proposed and fabricated using selective metalorganic chemical vapor deposition (MOCVD) technique. The proposed HBT features a triangular void over SiO2 stripe. The extrinsic base-collector capacitance is significantly reduced due to the isolation of the extrinsic collector region from the collector metal-contact by the void. The DC current-voltage characteristics of the selectively grown HBT are similar to those of the conventional one. However, the microwave performance is improved due to the reduced base-collector capacitance in the selectively grown HBT. For the device with two 3 x 10 mu m(2) emitter fingers, the selectively grown HBT has a maximum oscillation frequency 1.4 times higher than that of the conventional device, and the current gain cutoff frequency f(T) of 43 GHz and the maximum oscillation frequency f(max) of 20.5 GHz are obtained.