Heterojunction bipolar Transistor.

摘要

A heterojunction bipolar transistor includes an emitter layer (11) of a first conductivity type, a base layer (12) of a second conductivity type adjacent to the emitter layer, a collector buffer layer (13) of the first conductivity type, and a collector layer (14, 15) arranged between the collector buffer layer and the base layer. The collector layer includes a first collector layer (14) formed at the side of the base layer and a second collector layer (15) arranged at the side of the collector buffer layer. The first collector layer is a semiconductor layer having an impurity concentration lower than that of the base layer. The second collector layer is a semiconductor layer of the second conductivity type having an impurity concentration higher than that of the first collector layer.