Patent ID: 8803156

Claim:
A heterojunction bipolar transistor comprising: a substrate including an active region in the substrate laterally bordered by shallow trench insulation regions; a base region extending vertically above at least a portion of the active region; a base window trench, having sidewalls, extending vertically above the active region and extending laterally between the shallow trench insulation regions; an epitaxial seed layer having a monocrystalline portion and a polycrystalline or amorphous portion; an emitter region formed on the base region; a grain boundary of the monocrystalline portion and the polycrystalline or amorphous portion at a junction between the shallow trench insulation regions and the active region, the grain boundary extending outwardly away from the emitter region toward the sidewalls of the base window trench; and a base contact laterally displaced with respect to the emitter region and separated from said emitter region by a spacer.