Selective self-aligned emitter ledge formation for heterojunction bipolar transistors

We have demonstrated a heterojunction bipolar transistor (HBT) structure and fabrication process which produces a self-aligned emitter passivation ledge without the use of a realigned photoresist mask or additional dielectric etch masks. The novel HBT structure utilizes dual etch-stop layers in the emitter to allow the fabrication of a ledge using a simple, selective, wet-chemical etch process. This ledge technology has been successfully demonstrated in the InGaP/GaAs HBT material system.