Direct Observation of Lateral Coupling Between Self-Assembled Qauntum Dots

We report on high-resolution photoluminescence (PL) spectroscopic and microscopic study of laterally coupled InAs/GaAs self-assembled quantum dots by using a low-temperature near-field scanning optical microscope. We have observed slightly split PL spectra, which are associated with the bonding (symmetric) and antibonding (antisymmetric) energy states between two coupled quantum dots, closely located each other as confirmed by spatial mapping of the PL intensity. The experime...

We present an optical study of closely-spaced self-assembled InAs/GaAs quantum dots. The energy spectrum and correlations between photons subsequently emitted from a single pair provide not only clear evidence of coupling between the quantum dots but also insight into the coupling mechanism. Our results are in agreement with recent theories predicting that tunneling is largely suppressed between nonidentical quantum dots and that the interaction is instead dominated by dipole...

We report the fabrication and photoluminescence properties of laterally-coupled GaAs/AlGaAs quantum dots. The coupling in the quantum dot molecules is tuned by an external electric field. An intricate behavior, consisting of spectral line crossings and avoided crossings is observed for different molecules. Anticrossing patterns in the photoluminescence spectra provide direct evidence of the lateral coupling between two nearby quantum dots. A simple calculation suggests that t...

We use photoluminescence spectroscopy to investigate the ground state of single self-assembled InGaAs lateral quantum dot molecules. We apply a voltage along the growth direction that allows us to control the total charge occupancy of the quantum dot molecule. Using a combination of computational modeling and experimental analysis, we assign the observed discrete spectral lines to specific charge distributions. We explain the dynamic processes that lead to these charge config...

Tunneling excitations of electrons in dry-etched modulation-doped AlGaAs/GaAs coupled quantum dots (QDs) are probed by resonant inelastic light scattering. A sequence of intra- and intershell excitations are found at energies determined by the interplay between the QD confinement energy $\hbar \omega_0$ and the tunneling gap $\Delta_{SAS}$, the splitting between the symmetric and anti-symmetric delocalized single particle molecular states. The narrow line-widths displayed by ...

We investigate the photoluminescence temperature dependence of individual InAs/InGaAlAs quantum dots emitting in the optical telecommunication bands. The high-density dots are grown on InP substrates and the selection of a smaller dot number is done by the processing of suitable nanometer sized mesas. Using ensembles of only a few dots inside such mesas, their temperature stability, inter-dot charge transfer, as well as, carrier capture and escape mechanisms out of the dots a...

Lateral quantum dot molecules consist of at least two closely-spaced InGaAs quantum dots arranged such that the axis connecting the quantum dots is perpendicular to the growth direction. These quantum dot complexes are called molecules because the small spacing between the quantum dots is expected to lead to the formation of molecular-like delocalized states. We present optical spectroscopy of ensembles and individual lateral quantum dot molecules as a function of electric fi...

Single semiconductor quantum dots have been widely studied within devices that can apply an electric field. In the most common system, the low energy offset between the InGaAs quantum dot and the surrounding GaAs material limits the magnitude of field that can be applied to tens of kVcm^-1, before carriers tunnel out of the dot. The Stark shift experienced by the emission line is typically 1 meV. We report that by embedding the quantum dots in a quantum well heterostructure t...

We report on linewidth analysis of optical transitions in InAs/GaAs coupled quantum dots as a function of bias voltage, temperature, and tunnel coupling strength. A significant line broadening up to 100 $\mu$eV is observed at hole tunneling resonances where the coherent tunnel coupling between spatially direct and indirect exciton states is maximized, corresponding to a phonon-assisted transition rate of 150 ns${}^{-1}$ at 20 K. With increasing temperature, the linewidth show...

We have fabricated superconductor-quantum dot-superconductor (SC-QD-SC) junctions by using SC aluminum electrodes with narrow gaps laterally contacting a single self-assembled InAs QD. The fabricated junctions exhibited clear Coulomb staircases and Coulomb oscillations at 40 mK. Furthermore, clear suppression in conductance was observed for the source-drain voltage $|V_{\rm SD}| < 2\Delta/e$, where $\Delta$ is the SC energy gap of Al. The absence of Josephson current that flo...