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

We report a fabrication technique for 1 mu m wide emitter finger InP/GaAs0. 51Sb0.49/InP double heterojunction bipolar transistors (DHBTs). In this tec hnology, 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 In P/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 th e GaAs0.51Sb0.49 base conduction band edge lies 0.18 eV above the InP colle ctor conduction band, thus enabling the implementation of InP collectors fr ee 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 o f n(B) = 1.05 and n(C) = 1.00 and DHBTs with cutoff frequencies as high as 106 GHz and breakdown voltages of BVceo = 8 V have been implemented, and re present the highest performance ever achieved in this material system. The low turn-on and offset voltages make InP/GaAs0.51Sb0.49/InP DHBTs attractiv e for long talk-time wireless communication systems, yet these devices can also be adapted to power applications by virtue of their InP collector. Exc ellent performances are obtained without the need for complex and critical optimizations thanks to the favorable band lineups: all junctions are abrup t and no grading was performed in doping or in material composition. (C) 20 00 American Vacuum Society. [S0734-2101(00)09302-7].