Patent ID: 7821037
Filing Date: 2010-10-26
Classification: H01L

Abstract:
1. A heterojunction bipolar transistor, comprising: a subcollector layer of a first conductivity type; a first collector layer formed on the subcollector layer, the first collector layer containing an impurity of the first conductivity type; a third collector layer formed on the first collector layer, the third collector layer containing an impurity of the first conductivity type at a higher concentration than the first collector layer; a second collector layer formed on the third collector layer, the second collector layer containing an impurity of the first conductivity type at a lower concentration than the first collector layer; a base layer of a second conductivity type formed on the second collector layer; an emitter layer of the first conductivity type formed on the base layer, the emitter layer containing a semiconductor with a wider bandgap than the base layer; and an emitter cap layer of the first conductivity type formed on the emitter layer, wherein the first collector layer, the second collector layer and the third collector layer are made of the same semiconductor material.