Miniband conduction of minority electrons and negative transconductance by quantum reflection in a superlattice transistor

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Abstract
Transport of electrons tunnel injected into a superlattice (SL) is studied. The SL is placed in the base of an n‐p‐n bipolar transistor. By varying the emitter‐base forward bias (VEB), the energy of electrons injected into the base is varied. From the emitter and collector current measurements in the 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 VEB at the onset of miniband conduction and at the suppression of injection into the SL due to enhanced quantum reflection by the SL minigap. The transfer characteristics also reveal a low‐current gain regime of electron transport below the onset of miniband conduction, implying conduction mediated by subminiband gap states.