Effects of heavily carbon-doped base layers on performance of submicron algaas/gaas heterojunction bipolar transistors

Abstract

Submicron heterojunction bipolar transistors (HBTs) with maximum frequency of oscillation,/max, of 91 GHz have been fabricated using a self-aligned technique and a very heavily carbon-doped (lO20 cm-3) base layer. Since the quenching of photoluminescence (PL) intensity in heavily-doped GaAs is mainly due to nonradiative recombination in the bulk material, while contribution from surface recombination is negligible, the use of a heavily carbon-doped base layer in AlGaAs/GaAs HBTs minimizes 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 when the emitter width is scaled down to submicron (0.6 ¡j, m) dimensions. © 1993 The Japan Society of Applied Physics.