A depletion stop double base phototransistor: A demonstration of a new transistor structure

We introduce a simple but useful concept of depletion stop and demonstrate a transistor structure that makes use of this idea. This depletion stop transistor is grown by molecular beam epitaxy (MBE) on GaAs substrates. The base region is composed of a lightly doped layer near the emitter junction and a heavily doped layer near the collector junction. The edge of the depletion region at the emitter junction is designed to stop at the lightly doped base. When operated as a phototransistor, the depletion stop transistor shows a DC optical gain of 10. Further applications of this idea to the fabrication of a depletion stop double emitter double base transistor and to the Si-based device are also discussed.