Boron doping of SiGe base of heterobipolar transistors

The base of heterobipolar transistor can be doped to much higher levels than can the base of the homojunction transistor. We describe the principle, operation and effusion properties of a home-made boron source for p-type doping of the SiGe base of the heterobipolar transistor. Transistors fabricated from the material grown by molecular beam epitaxy, with a boron-doped base, exhibit good d.c. characteristics. A current gain of β max = 1000 could be obtained with 10 18 cm −3 base doping.