SELECTIVE SELF-ALIGNED EMITTER LEDGE FORMATION FOR HETEROJUNCTION BIPOLAR-TRANSISTORS

We have demonstrated a heterojunction bipolar transistor (HBT) structu re and fabrication process which produces a self-aligned emitter passi vation ledge without the use of a realigned photoresist mask or additi onal 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 syst em.