Small-geometry, high-performance, Si-Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors

Si-Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors (HBTs) with very heavily doped bases, fabricated using electron-beam lithography to obtain very small feature sizes, are discussed. Emitter, base, and collector epitaxial layers were grown in situ in a lamp-heated, chemical-vapor-deposition reactor. Transistors with common-emitter current gain of approximately 50 and f/sub t/ of about 28 GHz have been obtained. Analysis indicates that the frequency response is limited by parasitic resistances and capacitances in the simple demonstration structure used, rather than by the intrinsic device characteristics. Simple ring oscillators have been fabricated using HBTs in the inverse-active mode of operation.<
>