Lightly doped emitter HBT for low-power circuits

Abstract

We report an approach to reduce the base-emitter capacitance in AlGaAs-GaAs heterojunction bipolar transistors (HBT's) by adding a lightly doped emitter (LDE) region together with appropriate planar (/spl delta/) doping region to a conventional base-emitter junction. This improves both the f/sub t/ and /spl beta/ for low collector current density (J/sub c/) operation while preserving the high peak f/sub t/ at high J/sub c/. When applied to a current mode logic 128/129 programmable prescaler, the LDE HBT results in a reduction in power dissipation and improved bandwidth without any circuit modifications.