InGaP/GaAsSb/InGaAsSb double heterojunction bipolar transistors with 703-GHz fmax and 5.4-V breakdown voltage

This letter presents the current-gain and high-frequency characteristics of double heterojunction bipolar transistors (DHBTs) consisting of an n-InGaP emitter, a p-GaAsSb/p-InGaAsSb base, and an n-InP collector. The impact of the thickness of the first base metal (Pt) on the base contact resistivity is investigated in a p-GaAsSb/p-InGaAsSb test structure for the purpose of improving f(max). A low base contact resistivity (4.8 Omega mu m(2)) is obtained when the Pt layer is thinner than the p-GaAsSb layer. A fabricated InGaP/GaAsSb/InGaAsSb DHBT with a 0.25-mu m emitter exhibits a high current gain of 33 even though the base sheet resistance is as low as 1025 Omega/sq. The DHBT also exhibits an f(max) of 703 GHz and a breakdown voltage of 5.4 V. These results demonstrate that this DHBT technology is useful for fabricating high-speed integrated circuits with high output voltages.