Process development for small-area GaN/AlGaN heterojunction bipolar transistors

A self-aligned fabrication process for small emitter contact area (2 x 4 mum(2)) GaN/AlGaN heterojunction bipolar transistor is described. The process features dielectric-spacer sidewalls. low damage dry etching, and selected-area regrowth of GaAs(C) on the base contact. The junction current-voltage (I - V) characteristics were evaluated at various stages of the process sequence and provided an excellent diagnostic for monitoring the effect of plasma processes such as chemical vapor deposition or etching. A comparison is given with large emitter-area (1.96 X 10(3) mum(2)) devices fabricated on the same material. The small-area devices are attractive for microwave power switching applications provided a high-yield process can be developed. (C) 2001 American Vacuum Society.