Optical Spectroscopy of Laterally Spaced InAs/GaAs Quantum Dot Molecules
Date
2010
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
Over the past decade, potential device applications have fueled an extensive
effort to fabricate lateral arrays of quantum dots (QDs) with
specific dot densities, spacings and size distributions. An essential element
for the further development of QD devices with new functionalities
is the introduction of controllable quantum coupling between
two or more QDs in such an array. Tunable quantum coupling between
vertically stacked InAs QDs has been demonstrated, with the
coupling mediated by coherent tunneling and tunable with a static
electric field. While these studies have revealed that the spatial arrangement
of QDs can lead to remarkable effects, it will be impossible
to scale vertical coupling to a large number of QDs. Investigations
of lateral quantum coupling have been slower to develop, however,
because special growth protocols are required and the ability to independently
tune the luminescence energy of separate QDs is lost.
Spectroscopy of single pairs of laterally separated QDs is required to
resolve the signatures of quantum coupling from inhomogeneously
broadened ensemble spectra. Laterally-coupled quantum dots require
modified sample preparation methods to isolate single pairs of QDs
and apply electric fields that tune the relative energies of the two dots.
The electric field must be applied along the surface of the sample, perpendicular
to the growth direction. To apply this lateral field, we use
interdigitated electrodes patterned onto the sample surface with photolithography
and metal deposition. Electrical connections are made
to each of the interdigitated top contacts as well as to an ohmic back
contact. This three-terminal arrangement makes it possible to independently
control both the relative energies of the dots and the charging
of the QDs. We present photoluminescence spectra of laterally
coupled QDs whose coupling and charge states are tuned with this
three-terminal arrangement. We further discuss the implications and
opportunities for control of quantum coupling in laterally-scalable architectures.