SELF-ALIGNED ALGAAS GAAS HBT WITH SELECTIVELY REGROWN OMVPE EMITTER/

A novel self-aligned HBT mesa fabrication process utilizing selective OMVPE is reported whereby the extrinsic base has been made considerabl y thicker than the intrinsic base, thus avoiding the conventional trad e-off between base resistance and base transit time. This technique al so simplifies processing by eliminating the need for emitter isolation by etching or ion implantation prior to base metallization. Applicati on of this process to AlGaAs/GaAs N-p-n HBT's has yielded an intrinsic to extrinsic base sheet resistance ratio of 1.5, an f(T) of 22 GHz, a nd an f(max) of 55 GHz.