AlGaAs/GaAs bipolar transistors with a modulation-doped superlattice emitter

A new emitter-base concept for heterojunction bipolar transistors is proposed and demonstrated. The abrupt or graded emitter-base heterojunction drawbacks are circumvented by means of a modulation-doped stack of ternary compound alternating with binary compound layers. This stack provides efficient barriers to the hole current while preserving good diode characteristics. These concepts are demonstrated by experimental results on small-area devices with a common-emitter gain of ~40 and a collector-emitter voltage offset of ~80mV.