COHERENT RESONANT-TUNNELING IN AC FIELDS

We have analyzed the tunneling transmission probability and electronic current density through resonant heterostructures in the presence of an external electromagnetic field. In this work, we compare two differ ent models for a double barrier: In the first case the effect of the e xternal field is taken into account by spatially dependent ac voltages and in the second one the electromagnetic field is described in terms of a photon field that irradiates homogeneously the whole sample. Whi le in the first description the tunneling takes place mainly through p hotosidebands, in the case of homogeneous illumination the main effect ive tunneling channels correspond to the coupling between different el ectronic states due to photon absorption and emission. The difference of tunneling mechanisms between these configurations is strongly refle cted in the transmission and current density which present very differ ent features in both cases. In order to analyze these effects we have obtained, within the transfer Hamiltonian framework, a general express ion for the transition probability for coherent resonant tunneling in terms of the Green's function of the system.