Patent ID: 7859030
Filing Date: 2010-12-28
Classification: H01L

Abstract:
1. A heterojunction bipolar transistor having a base region made of SiGe mixed crystal, wherein: the base region includes: an intrinsic base region having junctions with a collector region and an emitter region; and an external base region for connecting the intrinsic base region with a base electrode, the intrinsic base region and the external base region are doped with a first impurity of a given conductivity type, and the external base region is doped with the first impurity in a higher concentration than the intrinsic base region, the external base region is further doped with a second impurity, and the concentration of the second impurity in the intrinsic base region is different from the concentration of the second impurity in the external base region, the first impurity is smaller in atomic radius than Si, the second impurity is larger in atomic radius than Si, the second impurity is made of Ge, the first impurity is made of boron, the intrinsic base region is made of SiGe mixed crystal having a composition of Si the external base region is made of SiGe mixed crystal having a composition of Si the Ge concentration of the external base region satisfies where B