Abstract
InP/InGaAs heterojunction bipolar transistors (HBTs), using a new crystallographically defined emitter contact technology for a self-aligned base-to-emitter structure, are fabricated and their performances are investigated. In this technology, a new self-alignment process has been developed based on the crystallographic wet etching characteristics of an InP dummy emitter layer, which is grown on the conventional HBT layer structure. The shape of the emitter contact, which is determined by the crystallographically etched sidewall profile of the InP dummy emitter layer, is used to obtain the desired contact spacing between the emitter mesa and the base contact by controlling only the thickness of the InP dummy emitter layer. The fabricated HBTs show good overall device performance at high frequencies with a current gain cutoff frequency fT of 94 GHz and a maximum oscillation frequency fmax of 124 GHz. The microwave power performance of the device was also measured and characterized.