RESONANT-TUNNELING IN TIME-PERIODICALLY MODULATED SEMICONDUCTOR NANOSTRUCTURES

We consider a semiconductor (AlGaAs/GaAs/AlGaAs) double-barrier resona nt tunneling nanostructure (DBRTS), in which the bottom of the potenti al well is modulated by an external periodic potential V(t) = V-mod co s Omega t. We examine the resonance response to both mono-energetic an d spatially localized incident electrons, extending previous results i n three ways. First, we study numerically the resonant characteristics in the transmission probabilities as functions of both the electron's energy and the frequency of the external field. We find that new low- frequency resonant peaks appear in the frequency dependence of the tra nsmission probabilities and discuss the origin and possible experiment al observation of these peaks. Second, we develop an analytic perturba tion theory (valid for small values of the parameter lambda = V-mod/h Omega) describing the processes of absorption and emission of single q uanta of the modulation field and show that this perturbative treatmen t agrees well with the results of numerical calculations in the approp riate regions, up to and including the regime in which the one-quantum processes saturate. Third, for localized (Gaussian) incident wave pac kets, we show numerically that temporal modulations of the potential w ell in the DBRTS can induce spatial modulations in the transmitted and reflected wave packets. We develop a simple qualitative picture that explains our results. Finally, we estimate characteristic values of th e parameters relevant for possible observation of these effects in lab oratory experiments.