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 3×10 µ m2 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.