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 considerably thicker than the intrinsic base, thus avoiding the conventional trade-off between base resistance and base transit time. This technique also simplifies processing by eliminating the need for emitter isolation by etching or ion implantation prior to base metallization. Application 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, and an f(max) of 55 GHz.