Patent ID: 6492711
Filing Date: 2002-12-10
Classification: H01L

Abstract:
A heterojunction bipolar transistor comprising a first semiconductor layer made from semiconductor material containing Si as a component; a second semiconductor layer made from semiconductor material containing Si, Ge and C as components having a band gap narrower than the first semiconductor layer and consisting of a top layer, a center layer and a bottom layer; a third semiconductor layer made from Si as a component, and having a band gap wider than the second semiconductor layer stacked in this order onto a substrate; and a heterojunction barrier provided between the first semiconductor layer and the second semiconductor layer,said heterojunction bipolar transistor further comprising: a collector layer formed in the first semiconductor layer and containing a first conductive impurity; a base layer formed in the second semiconductor layer and containing a second conductivity impurity; and an emitter layer formed in the third semiconductor layer and containing a first conductivity impurity, the second semiconductor layer having an average lattice strain of 1.0% or less; wherein the first semiconductor layer is made of Si single crystal; and when the second semiconductor layer has a composition represented by Si1âˆ’xâˆ’yGexCy where x is a Ge content and y is a C content, the composition is in a region surrounded by following four straight lines: straight line {circle around (1)}: y=0.122xâˆ’0.032 straight line {circle around (2)}: y=0.1245x+0.028 straight line {circle around (3)}: y=0.2332xâˆ’0.0233 (C content is 22% or less) straight line {circle around (4)}: y=0.0622x+0.0127 (Ge content is 22% or less) on two-dimensional rectangular coordinates whose horizontal axis and vertical axis indicate the Ge content and the C content, respectively; wherein the center layer of the second semiconductor layer has the Ge content and the C content uniformly; wherein in the top layer of the second semiconductor layer, the C content increases in a direction from the third semiconductor layer to the center layer.