Si/SiGe heterojunction bipolar transistor made by molecular-beam epitaxy

Si/SiGe heterostructure bipolar transistors (HBTs) were fabricated and compared to Si homojunction transistors with similar doping levels. Low-temperature Si-MBE (molecular-beam epitaxy) was used to form the heterojunction and the homojunction layer sequences. A wet chemical selective etching technique was used to contact the thin (80 nm) base layer of the heterojunction transistor. A peak current gain of 200 to 400 was measured for the heterostructure devices, compared to a gain of two for the homojunction structure. The current gain collector current dependence of the heterostructure device could be due to surface recombination effects. >