Heterojunction biopolar transistor and manufacturing method

A heterojunction bipolar transistor comprising:

• a substrate including an active region in the substrate bordered by at least one shallow trench insulation region;
• a base region extending vertically above at least a portion of the active region;
• a base window trench, having sidewalls, extending laterally beyond the active region and vertically to the active region;
• at least one STI trench extending laterally between the active region and at least one of said shallow trench insulation regions, and extending into at least a portion of at least one of said shallow trench insulation regions;
• an emitter region formed on the base region;
• a grain boundary of the monocrystalline portion and a polycrystalline or amorphous portion in the at least one STI trench and 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.