MBE-grown Ge/GaAs heterojunction bipolar transistors operated at 300 K and 77 K with current gain of 45

The authors report the first fabrication of Ge/GaAs heterojunction bipolar transistors (HBTs) grown by molecular-beam epitaxy (MBE). Ge/GaAs HBTs have advantages of lower voltage operation, lower base resistance, and lower contact resistance over GaAs/AlGaAs HBTs, when applied to the high-speed digital circuits. Si-doped (n=1*10/sup 17/ cm/sup -3/, 3000 A) emitter layer, nondoped (p=1*10/sup 19/ cm/sup -3/, 1000 A) Ge base layer, and Sb-doped (n=3*10/sup 17/ cm/sup 3/, 5000 A) Ge collector layer are sequentially grown on GaAs