Y. Isawa et al., EFFECT OF SPATIALLY VARYING POTENTIAL ON PHOTON-ASSISTED TUNNELING INQUANTUM DOTS, Journal of the Physical Society of Japan, 66(1), 1997, pp. 11-14
A formula for photon-assisted tunnelling (PAT) in semiconductor quantu
m dots is derived for a case of low transmission rates through tunnell
ing barriers, by using the generalized perturbation method developed b
y Keldysh. We describe a new process giving rise to a de current even
in the absence of bias voltage in which the dot is excited uniformly b
y an ac signal including microwaves, and both the occupied and the uno
ccupied quantized states participate in the electrical conduction. In
addition, the de current flows through the left and the right barriers
via different levels. An electron tunnels into the dot from the barri
er in which the higher energy level pumped by absorbing a spatially un
iform ac signal has a higher transfer rate and another one occupied in
the lower level tunnels out through the barrier in which the lower en
ergy level has a higher transfer rate. This is in marked contrast to a
de current without bias voltage, which has been explained in terms of
the process making use of a single quantized state in an asymmetrical
ly excited quantum dot. In order to open a new channel, it is necessar
y to prepare a particular level configuration, which is realized, for
instance, by spatially varying the potential.