InP/GaAs0.51Sb0.49/InP fully self-aligned double heterojunction bipolar transistors with a C-doped base:: preliminary reliability study

A preliminary reliability study is reported for carbon-doped InP GaAs0.51Sb0.49/InP NpN double heterojunction bipolar transistors (DHBTs) lattice-matched to InP substrates. These DHBTs rake advantage of the staggered ("type II") band lineup at InP/GaAs0.51Sb0.49 interfaces: in this system, the GaAs0.51Sb0.49 base conduction band edge lies 0.15-0.18 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 offset voltages, low emitter-base turn-on voltages, and very nearly ideal base and collector current characteristics with excellent junction ideality factors. Cut-off frequencies in excess of 100 GHz have been measured, making InP/GaAsSb DHBTs very attractive for wireless communication systems. InP/ GaAs0.51Sb0.49 heterojunctions have so far received little attention in the literature, and no reliability information is available for this promising material combination. We have found that electrical stressing at moderate bias in fully self-aligned non-passivated devices results in a rapid, and reversible, degradation of device properties which is manifested through an increase of the base current ideality factor n(B). On the other hand, the collector current remains unchanged, indicating that there is no dopant migration effect under the test conditions used here. (C) 1999 Elsevier Science Ltd. All rights reserved.