LPE-Grown InGaAsP/InP heterojunction bipolar phototransistors

InGaAsP/InP heterojunction bipolar phototransistors have been produced for the first time. The fabrication and characterization of these devices will be discussed, and the potential application of quaternary heterojunction bipolar phototransistors as high speed photodetectors in optical fiber systems is explored. The present devices were fabricated by liquid phase epitaxy and consist of an n-InP collector, a p⁺-InGaAsP base (Mg-doped), and an n-InP emitter on an n⁺-InP substrate. Individual devices were formed by etching 200 µm diameter mesas through the three LPE layers; there was no base contact. In spite of the relatively wide base in these initial devices, an optical gain greater than 20 was measured for input powers greater than 1 µW. Pulse response times are below 50 nsec.