Ge ion implantation in Si for the fabrication of Si/GexSi1 - X heterojunction transistors

Epitaxial Si/GexSi1 - x heterojunctions were formed by high dose Ge ion implantation in Si followed by solid phase epitaxy. This technique was adopted for fabricating Si/GexSi1 - x heterojunction n-p-n bipolar transistors (HBT). We used a standard self-aligned, double polycrystalline silicon process for Si with the addition of the high dose Ge implantation. The transistors are characterized by a 60 nm wide neutral base with a Ge concentration peak of ,âà 8 at.% at the base-collector junction. The devices show very good static electrical characteristics, and compared with Si homojunction transistors with similar values of current gain and Early voltage, show base resistances more than two times lower. In addition to the HBTs, also the feasibility of GexSi1 - x metal-oxide-semiconductor field-effect transistors (MOSFET) by ion implantation has been explored by investigating the GexSi1 - x oxidation process.