Band-gap narrowing and high-frequency characteristics of Si/Ge/sub x/Si/sub 1-x/ heterojunction bipolar transistors formed by Ge ion implantation in Si

Si/Ge/sub x/Si/sub 1-x/ heterojunction n-p-n bipolar transistors (HBT's) with a double-polysilicon self-aligned structure were fabricated by using high dose Ge implantation for the formation of the Si/Ge/sub x/Si/sub 1-x/ heterostructure and As and BF/sub 2/ implantation for emitter and base doping. DC and high frequency electrical characteristics are investigated for Ge concentrations up to 7 at.% and for base widths down to 35 nm. Improvements in electrical characteristics compared to reference Si transistors are demonstrated. Experimental data indicating that these improvements are related to an effective band gap engineering are shown and discussed.