Kabushiki Kaisha Toshiba

Masao Obara

Tetsuro Nozu

Norio Iizuka

Junko Akagi

Torakiti Kobayashi

An AlGaAs/GaAs heterojunction bipolar transistor in which a base doping concentration is set to be as very high as 5.times.10.sup.19 cm.sup.-3 or more to cause a band gap narrowing effect and to reduce a band gap difference by an amount corresponding to the band gap narrowing effect, an Al composition ratio, i.e., x in an Al.sub.x Ga.sub.1-x As material of an emitter layer is set to be less than 0.25, whereby an emitter resistance can be made small, an operating speed can be made fast and a current gain can be made high. Preferably, the base doping concentration is set to be 1.2.times.10.sup.20 cm.sup.-3 or more so that the operation speed can be made remarkably fast.

Heterojunction bipolar transistor

A heterojunction bipolar transistor comprises n.sup.+ -type GaAs collector contact region, an n-type GaAs collector region, a p.sup.+ -type GaAs base region, an n-type AlGaAs emitter region, and an n.sup.+ -type InGaAs emitter contact region, all of which are formed on a semiinsulative GaAs substrate. A heterojunction is formed by the base region and the emitter region. The emitter region is formed in mesa shape by dry etching. Around this mesa, B.sup.+ ion-implanted high-resistance region is formed. The base-emitter Junction is isolated from the ion-implanted region. The heterojunction bipolar transistor therefore has little on-voltage changes.

Growing community of inventors

Tokyo, Japan

Masao Obara