Miniband Conduction of Minority Electrons in a Superlattice Transistor.

Transport of electrons tunnel-injected into a superlattice (SL) is studied. The SL is placed in the base of a n-p-n bipolar transistor. By varying the emitter-base forward bias (V sub (EB)), the energy of electrons injected into the base is varied. From the emitter and collector current measurements in common - base configuration, it is found that the electron transmission to the collector is strongly dependent on the injection energy, the currents showing a sharp peak and the associated negative transconductance. The measurements show excellent agreement with the calculated values of V sub (EB) at the onset of miniband conduction and at the threshold of suppression of injection into the SL-miniband. The transfer characteristics also reveal a low current gain regime of electron transport below the onset of miniband conduction, implying conduction mediated by sub- miniband gap states.