Much experimental research has been performed in the equilibrium regime
on individual quantum dots and quantum point contacts (QPCs). The focus of the
research presented here is electron transport in the nonequilibrium regime in coupled
quantum dot and QPC systems fabricated on AlGaAs/GaAs material using the split
gate technique.
Near equilibrium magnetoconductance measurements were performed on a
quantum dot and a QPC. Oscillations were seen in the conductance of the sensor
which corresponded to Aharonov-Bohm oscillations in the quantum dot, to our
knowledge the first such observation. Sudden jumps in the conductance of the QPC
were observed under certain gate biases and under certain magnetic fields. When
the gate biases and magnetic field were held constant and the conductance was
observed over time, switching was observed with the form of a random telegraph
signal (RTS). RTS switching is usually attributed to charging of a single impurity.
However, in this case switching may have been due to tunneling via edge states in
the dot.
Nonequilibrium transport in single quantum dots was investigated. A knee
or kink was observed in the current-voltage characteristics of two dots on different
material. The bias conditions under which the knee occurred point to electron
heating as the physical mechanism for the observed behavior. However, the data
can not be fit accurately over all bias ranges with an energy balance hot electron
model. Modifications to the model are needed to accurately represent the devices
studied here.
Finally, the effect of nonlinear transport through a one dimensional (1D) QPC
on the equilibrium conductance of an adjacent OD quantum dot was explored. This
was the first attempt to observe Coulomb drag between a OD and 1D system. It
was observed that the equilibrium conductance peaks in the quantum dot were
broadened as the current in the QPC increased. This apparent electron heating
effect in the dot can be explained by a simple ballistic phonon model. However,
reasonable phase coherence times can be estimated from peak fitting using a Breit-
Wigner formula which points to a Coulomb interaction. More detailed numerical
calculations should illuminate the dominant scattering processes. / Graduation date: 1999
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33515 |
| Date | 15 March 1999 |
| Creators | Krishnaswamy, Anasuya Erin |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0035 seconds