GaAs/AlxGa1−xAs depletion stop phototransistor grown by molecular beam epitaxy

We introduce a simple but useful concept of depletion stop and demonstrate a phototransistor that makes use of this idea. This depletion stop phototransistor is grown by molecular beam epitaxy 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. A dc optical gain ≳10 has been successfully observed. Further applications of this idea to the fabrication of a depletion stop double emitter double base transistor and to the Si-based devices are also discussed.