Device technology of InP/InGaAs HBTs for 40-Gb/s optical transmission application

Several techniques that enable high-yield fabrication of high-performance high-thermal-stability InP/InGaAs heterojunction bipolar transistors (HBTs) for use in 40-Gb/s ICs were developed. The T-shaped emitter electrode structure provides a simple fabrication process. A highly-C-doped base and a new Pt/Ti/Mo/Ti/Pt/Au metal system result in a thin base and low base resistance. An InP subcollector suppresses thermal runaway at high collector current. Using these techniques, an extremely high cutoff frequency f/sub T/ of 235 GHz was achieved for an HBT, along with a static 1/2 frequency divider operating up to 44 GHz.