Patent ID: 7301181

Claim:
A heterojunction bipolar transistor comprising: an n-type collector layer made of GaAs; a p-type base layer made of GaAs and formed on said collector layer; an n-type or non-doped first emitter layer formed on said base layer, an n-type second emitter layer formed on said first emitter layer; and a base electrode formed on said base layer so as to contact at least one of said first emitter layer and said second emitter layer, wherein said first emitter layer is made of a semiconductor material including aluminum, and has a thickness ranging from 3 nm to less than 10 nm, wherein said second emitter layer is made of In x Ga 1-x P (0<x<1), wherein said base electrode is formed by thermally diffusing metal on at least one of said first emitter layer and said second emitter layer so that said base electrode contacts said base layer, and wherein said first emitter layer is made of an aluminum oxide.