Fabrication of self‐aligned GaAs/AlGaAs and GaAs/InGaP microwave power heterojunction bipolar transistors

Self‐aligned processing of high efficiency power heterojunction bipolar transistors (HBTs) using implant isolation, selective wet and dry etching for mesa formation, plasma‐enhanced chemical vapor deposited SiNx for sidewall spacers and through‐wafer via connections is reported. GaAs/AlGaAs and GaAs/InGaP HBTs grown by metalorganic molecular beam epitaxy utilizing carbon for high, well‐confined base doping produced power‐added efficiencies of 63%, power gain of 10 dB and output power of 1.7 W at 4 GHz for twelve 2×15 μm2 double‐emitter finger devices (GaAs/AlGaAs) and 57% power‐added efficiency, power gain of 11.3 dB and output power of 0.6 W at 4 GHz (GaAs/InGaP), respectively.