LIGHTLY DOPED EMITTER HBT FOR LOW-POWER CIRCUITS

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