Design and performance of InP/GaAsSb/InP double heterojunction bipolar transistors

Abstract

We report a fabrication technique for 1 μm wide emitter finger InP/GaAs0.51Sb0.49/InP double heterojunction bipolar transistors (DHBTs). In this technology, we use a wet-etched undercut airbridge technique to provide device isolation while minimizing parasitics and avoiding damage to semiconductor layers by dry etching. The metalorganic chemical vapor deposition-grown InP/GaAs0.51Sb0.49/InP NpN structure takes advantage of a staggered (“type II”) band lineup at InP/GaAs0.51Sb0.49 interfaces: in this material system the GaAs0.51Sb0.49 base conduction band edge lies 0.18 eV above the InP collector conduction band, thus enabling the implementation of InP collectors free of the collector current blocking effect encountered in conventional Ga0.47In0.53As base DHBTs. The structure results in very low collector current offset voltages, low emitter-base turn-on voltages, and very nearly ideal base and collector current characteristics with junction ideality factors of nB=1.05 and nC=1.00 and DHBTs with cutoff frequencies as high as 106 GHz and breakdown voltages of BVceo=8 V have been implemented, and represent the highest performance ever achieved in this material system. The low turn-on and offset voltages make InP/GaAs0.51Sb0.49/InP DHBTs attractive for long talk-time wireless communication systems, yet these devices can also be adapted to power applications by virtue of their InP collector. Excellent performances are obtained without the need for complex and critical optimizations thanks to the favorable band lineups: all junctions are abrupt and no grading was performed in doping or in material composition.