Photon Assisted Tunneling in Single and Coupled Quantum Dot Systems
T. Fujisawa and S. Tarucha
We describe photon assisted tunneling (PAT) in single and coupled
quantum dot systems which have a relatively large zero-dimensional
(0D) level separation. A microwave electric field applied across
the tunneling barrier leads to the formation of a sideband
structure. For a single quantum dot system, a PAT current peak is
clearly observed in addition to the Coulomb oscillation peak. For a
weakly-coupled double-dot system, we observe resonant 0D-0D PAT.
The resonant PAT current appears only when two discrete quantum
levels in the neighboring dots are exactly separated by the
microwave photon energy. The PAT current shows a narrower peak than
the main resonant tunneling current in accordance with time-
dependent tunneling theory. The photon stimulated emission
associated with PAT from a higher-lying occupied level to a lower-
lying empty level is obtained at a drain voltage sufficient that
population inversion takes place.
You need the LATEX style file "spy.sty" from Academic Press (http://www.idealibrary.com).
Fig 1. Schematic diagram of the double gate single electron
transistor. A single and a coupled quantum dot are formed by
applying relevant voltages to the Schottky gates.
Fig. 2. Energy diagram of the PAT through a dot in the classical
Coulomb blockade regime (a), and in the quantum dot regime (b).
Fig. 3. A Coulomb oscillation peak and PAT current peaks through
a quantum dot. Each curve is offset by 0.2 pA for clarity.
Fig. 4. (a) Schematic charging diagram of the coupled dot system.
(n, m) corresponds to the number of electrons in the left dot and
in the right dot, respectively. The resonant 0D-0D tunneling peaks
are observed at the vertices, V and V'. The thick lines,
PLR, PRL, etc., indicate the conditions for the resonant 0D-0D PAT.
(b) Energy diagram of the PAT for the condition on the line PLR,
at the point V, and (d) on the line PRL.
Fig. 5. (a) The drain current profile near the condition V' with
and without applying microwave radiation. (b) The contour plot of the current
profile. A part of the charging diagram is also attached on the top
of the plot. The arrows indicate that E = (E_R + E_L)/2 and
e = E_R - E_L are changed.
Fig. 6. (a)The drain current profile with a main
resonance peak at V' and satellite PAT peaks on P'LR
(b) Schematic diagram for the photon absorption and stimulated emission