Silicon-germanium base heterojunction bipolar transistors by molecular beam epitaxy

We report the first SiGe base heterojunction Bipolar Transistors (HBT) The devices were fabricated using Molecular Beam Epitaxy (MBE), low temperature processing and different germanium contents. The transistors demonstrate current gain and show the expected increase in collector current as a result of reduced bandgap due to Ge incorporation in the base. A 6 times increase in collector current was measured for a 1000A base device containing 12% Ge, consistent with a bandgap shrinkage in the base of approximately 45 meV. For the homojunction transistors, base widths as thin as 800A were grown, corresponding to a neutral base width of only 500A. These devices have a 40% higher collector current than the equivalent devices with a 1000A base width.