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 GaAs0.51Sb 0.49/InP NpN double heterojunction bipolar transistors (DHBTs) lattice-matc hed to InP substrates. These DHBTs rake advantage of the staggered ("type I I") 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 collect or conduction band, thus enabling the implementation of InP collectors free of the collector current blocking effect encountered in conventional Ga0.4 7In0.53As base DHBTs. The structure results in very low collector offset vo ltages, low emitter-base turn-on voltages, and very nearly ideal base and c ollector current characteristics with excellent junction ideality factors. Cut-off frequencies in excess of 100 GHz have been measured, making InP/GaA sSb DHBTs very attractive for wireless communication systems. InP/ GaAs0.51 Sb0.49 heterojunctions have so far received little attention in the literat ure, and no reliability information is available for this promising materia l combination. We have found that electrical stressing at moderate bias in fully self-aligned non-passivated devices results in a rapid, and reversibl e, 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 ef fect under the test conditions used here. (C) 1999 Elsevier Science Ltd. Al l rights reserved.