Sharp Kabushiki Kaisha Corporation

Koken Yoshikawa

John Kevin Twynam

Toshiaki Kinosada

Motoji Yagura

Hiroya Sato

Masanori Kominami

An ohmic electrode structure is produced by developing an In.sub.x Ga.sub.1-x As layer epitaxially on a compound semiconductor (n-Ga As), and providing a barrier layer composed of a tungsten nitride (high melting point metallic nitride) by sputtering. Then, electrode patterning is performed on the top of the tungsten nitride barrier layer by the photo-resist technique. After the process, unnecessary portion of the tungsten nitride barrier layer is removed by the reactive ion etching (RIE). On the top of this a Ti layer, a Pt layer and an Au layer are deposited in layers in that order by the lift-off technique to form a metal layer. Here, molybdenum nitride or titanium nitride may be used in place of tungsten nitride.

Ohmic electrode structure for In.sub.x Ga.sub.1-x As layer

A hetero-junction bipolar transistor includes: a substrate; a first conductive type collector layer disposed on the substrate; a second conductive type base layer having an external base region; and a first conductive type emitter layer having a bandgap larger than the bandgap of the base layer disposed in this order, wherein the emitter layer includes a first emitter layer, an etching stop layer, and a second emitter layer disposed in this order starting from the substrate side; a base electrode is formed on the etching stop layer or the first emitter layer disposed on the external base region; a region of the first emitter layer on the base layer has a thickness such that the region is substantially depleted at all voltages applied when the transistor is normally operated; the second emitter layer has an electron affinity equal to or smaller than an electron affinity of the first emitter layer; and the etching stop layer has an electron affinity larger than the electron affinity of the first emitter layer, and has a thickness of approximately 3 nm.

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Ikoma, Japan

Koken Yoshikawa