SIMULATION STUDIES OF PHOTON-ASSISTED QUANTUM TRANSPORT

Direct numerical simulations were performed to investigate conditions for the strong effects of photon-assisted quantum transport. Transmiss ion probabilities of incident electrons as Gaussian wave packets were calculated for single- and double-barrier structures irradiated by ele ctromagnetic fields that were focused within a finite region xi(ac). W hen the period of the ac electromagnetic field is short compared with the time tau(xi ac), which is the traversal time of the electrons in t he region of the applied ac field, the transmission probability can be affected by photon emission and photon absorption. The magnitude of t hese effects strongly depends on the width xi(ac) and the bound-state character of the electrons. These dependences can be understood from t he selection rule, which results from the momentum conservation of the electron and photon system. Consequently, we have shown that photon-a ssisted transport over a single barrier is difficult to achieve in two -dimensional electron-gas devices due to the relatively long screening length. We have demonstrated, however, that the photon-assisted proce ss is significantly enhanced in double-barrier devices due to quasibou nd-to-extended-state transitions.