Patent ID: 8492794

Claim:
A heterojunction bipolar transistor (HBT) structure comprising an interface between a bottom surface of an emitter comprising a polycrystalline silicon portion and a planar top surface of a single crystalline germanium substrate including an entirety of a base and an entirety of a collector and embedding a shallow trench isolation structure therein, wherein said collector comprises a first single crystalline germanium portion having a doping of a first conductivity type; said base comprises a second single crystalline germanium portion epitaxially aligned to said collector and having a doping of a second conductivity type that is the opposite of said first conductivity type, wherein a horizontal top surface of said base is a portion of said planar top surface; said polycrystalline silicon portion of said emitter has a doping of said first conductivity type and contacts said top surface of said base; and said base has a same thickness throughout said second single crystalline germanium portion.