Nonequilibrium phonon generation in coupled Wannier-Stark ladders from a semiconductor superlattice in a three-terminal device

Abstract

We present an experimental and a theoretical study on the midinfrared electroluminescence associated with transitions between electric-field-induced conduction states, forming Wannier-Stark (WS) ladders, in a strongly coupled GaAs∕AlAs superlattice inserted in a heterostructure bipolar transistorlike device. Electroluminescence shows wide tunability (100–210meV) of the diagonal intra-WS radiative transition, up to the merging with the vertical inter-WS emission, at constant injected emitter current. Intra-WS linewidth analysis suggests electric field homogeneity on the whole superlattice for F⩾160kV∕cm, until intervalley electronic scattering limits the radiative efficiency above 230kV∕cm. In this range, the integral optical intensity is constant, as expected by a transistorlike optoelectronic device. Monte Carlo simulations give a good agreement between experimental and theoretical electroluminescence spectra. Theoretical investigation indicates that intersubband scattering via LO phonon is responsible for the population of the states of the excited ladder. It shows that transitions between WS ladder states are responsible for hot phonon generation at fixed momenta by inter- and intrasubband nonradiative transitions.