JPS6457666A - Heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To obtain a collector-top type heterojunction bipolar transistor having a high current amplification percentage by a method wherein at least the surface located in the vicinity of the boundary of an intrinsic transistor and an external base of the external base region formed outside an intrinsic transistor region is covered by a semiconductor layer having the band gap wider than that of the external base region. CONSTITUTION:At least three layers selected from the first conductivity type semiconductor layers 102 and 103 which become an emitter, the second conductivity type semiconductor layer 104 which becomes a base, and the first conductivity type third semiconductor layers 105 and 106 which become a collector are laminated successively, and the forbidden band width of at least a part of the first semiconductor layers 102 and 103 is formed wider than that of the second semiconductor layer 104. In such a heterojunction bipolar transistor above- mentioned, at least the surface in the vicinity of the boundary of the intrinsic transistor of the external base region 107 formed outside the intrinsic transistor region and external base region 107, is covered by the semiconductive material layer 108 having the band gap wider than that of the external base region 107.