Investigation of heterostructure-confinement-emitter transistors

In this paper we review our current investigation on heterostructure-confinement-emitter transistors, i.e. heterostructure-emitter bipolar (HEBT) and superlattice-emitter (SET), and then describe further advances in negative-differential-resistance (NDR) devices just utilizing GaAs-based materials. An improved HEBT using an Al_0.5Ga_0.5As as a confinement layer exhibits not only a common-emitter current gain of 180 but also a very small offset voltage of 80 mV when operated under a normal mode, which is much better than for a Al_0.3Ga_0.3As confinement layer. An S-shaped NDR phenomenon is observed when operating under reverse mode. On the other hand, instead of an AlGaAs bulk layer, a five-period AlGaAs/GaAs superlattice is employed as a confinement and tunneling barrier for the SET device. Experimentally, a common-emitter current gain of 65 (maximum of 95 at 300 K) and double N-shaped NDR performance with peak-to-valley ratios (PVRs) of 4 and 2.6 are obtained at 77 K. These discussions are followed by theoretical considerations and experimental analyses. It is found that the new devices studied are of considerable interest for a variety of potential applications that could be realized with greatly reduced circuit complexity.