Dual layer epitaxtial base heterojunction bipolar transistor

Abstract

A Si-SiGe-Si heterojunction bipolar transistor which has a very thin epitaxial base layer. The device possesses an optimum doping profile across a base layer. The emitter region is higher doping concentration of n.sup.+ -type. The base layer of p-type comprises both a monocrystalline SiGe layer having a lightly doped region on a collector side and a heavily doped region, and a lightly doped monocrystalline Si layer on an emitter side. An emitter side Si-SiGe heterojunction exists in the base layer and a collector side Si-SiGe heterojunction exists in the collector region. Those provides a slope negative gradient of a potential profile from the emitter to collector without a potential barrier for carriers, or electrons or holes. The very thin base layer is connected to an aluminium contact through an external base layer and a base contact layer thereby permitting the very thin base layer to be free from a damage by contacting with a metal such as aluminium. In replacement of this, the base layer may be formed thereunder with a base contact layer to cover the damage of the base layer.