Self-Aligned InP/InGaAs Single Heterojunction Bipolar Transistor with Novel Micro-airbridge Structure and Quasi-coplanar Contacts

The fabrication and performance of a self-aligned InP/InGaAs single heterojunction bipolar transistor (SHBT) with a novel micro-airbridge structure and co-planar-contacts are described. The reported structure is based on anisotropy wet, etching of InP and selective wet, etching between InP and InGaAs. The device with a 1.5 x 5μm² emitter demonstrats a current gain of 30 at collector current I_c = 10 mA and extrapolates the current-gain cutoff frequency F_t of 53 GHz and the maximum oscillation frequency F_max of 72 GHz. Compared to the one using the conventional structure, the maximum oscillation frequency of the device with micro-airbridge is dramatically improved from 45 GHz to 72 GHz. This result reveals that the extrinsic capacitance of small size SHBT can be greatly reduced.