GexSi1−x strained-layer heterostructure bipolar transistors

Double heterostructure bipolar transistors with the base region consisting of a p-Ge0.5Si0.5 strained-layer superlattice have been grown by molecular beam epitaxy. At a wavelength of 1.3 μm, optical gain as high as 52 has been achieved in two-terminal phototransistors. The large photocurrent is inferred to be a product of the transistor gain, on the order of 20, and avalanche multiplication. A differential current gain of 10 has been obtained in the three-terminal bipolar transistors. The incorporation of a narrow band-gap GexSi1−x superlattice base is expected to result in higher emitter injection efficiency as compared to Si bipolar transistors.