Applications of transition-emitter superlattice to bipolar transistors

A novel bipolar transistor with a superlatticed transition emitter has been fabricated and demonstrated at room tem­perature. The use of the i-Al_0.5Ga_0.5As/n⁺-GaAs superlattice allows electrons to transport and prevents holes from injecting, which improves the emitter injection efficiency. Since the AlGaAs layers in the superlattice are undoped, the problems of DX centers and persistent photoconductivity (PPC) effect can be reduced signhcantly. Furthermore, from the experimental results, the potential spike at the emitter-base interface is so small that it can be neglected. An extremely small collector offset voltage of 55 mV and the common-emitter current gain of about 65 have been simultaneously ob­tained at room temperature in the nonoptimized device. Consequently, the proposed device indeed exhibits good poten­tial for digital circuit applications.