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 u sing selective metalorganic chemical vapor deposition (MOCVD) techniqu e. The proposed HBT features a triangular void over SiO2 stripe. The e xtrinsic base-collector capacitance is significantly reduced due to th e isolation of the extrinsic collector region from the collector metal -contact by the void. The DC current-voltage characteristics of the se lectively grown HBT are similar to those of the conventional one. Howe ver, the microwave performance is improved due to the reduced base-col lector capacitance in the selectively grown HBT. For the device with t wo 3 x 10 mu m(2) emitter fingers, the selectively grown HBT has a max imum oscillation frequency 1.4 times higher than that of the conventio nal device, and the current gain cutoff frequency f(T) of 43 GHz and t he maximum oscillation frequency f(max) of 20.5 GHz are obtained.