EFFECTS OF HEAVILY CARBON-DOPED BASE LAYERS ON PERFORMANCE OF SUBMICRON ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS

Submicron heterojunction bipolar transistors (HBTs) with maximum frequ ency of oscillation, f(MAX), of 91 GHz have been fabricated using a se lf-aligned technique and a very heavily carbon-doped (10(20) cm-3) bas e layer. Since the quenching of photoluminescence (PL) intensity in he avily-doped GaAs is mainly due to nonradiative recombination in the bu lk material, while contribution from surface recombination is negligib le, the use of a heavily carbon-doped base layer in AlGaAs/GaAs HBTs m inimizes the influence of surface recombination in the extrinsic base region. Thus, for HBTs with a heavily doped base layer, the ''emitter size effect'' (degradation of HBT current gain) is greatly reduced whe n the emitter width is scaled down to submicron (0.6 mum) dimensions.