Coulomb interaction signatures in self-assembled lateral quantum dot molecules

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 configurations through electrical injection and optical generation. Our systemic analysis provides evidence of interdot tunneling of electrons as predicted in previous theoretical work.

Figure 1

(a) The layout of the self-assembled LQDMs in a Schottky diode. This structure applies an electric field strictly along the growth direction. (b) AFM image and (c) cross-sectional profile of single LQDM grown in the same condition as the sample we studied.

Figure 2

(a) PL spectrum of the ground-state transitions in LQDM 1 as a function of vertical voltage. (b) PL spectra of $X^0$ and $X^{+}/X^{+\prime }$ in six different LQDMs. Lines are guides to the eye. Energies are plotted relative to the emission of the $X^0$ state, with the absolute energy of the $X^0$ state indicated by the inset text. (c) Intensities of PL lines $X_R^0$, $X^{+}/X^{+\prime }$, and $X_L^0$ as a function of vertical voltage. (d) Intensity ratios of PL lines as a function of laser power densities under 0.41-V vertical voltage. (e) Theoretical modeling results of the energies and intensities of positive trion emissions in LQDMs based on the energies of neutral exciton emissions.

Figure 3

(a) Full PL spectra of the ground-state transition mapping as a function of vertical voltage measured for LQDM 1. (b) Electrical charging sequence as the applied voltage increases. (c) Comparison between the theoretical (solid and dashed lines in the left half of every column) and experimental (dotted lines in the right half of every column) emission energies from $X^{+}$ to $X^{2-}$. (d) Depiction of the initial and final states of each PL emission line.

Figure 4

(a) Full PL spectra of the ground-state transition mapping as a function of vertical voltage measured for LQDM 2. (b) Electrically charging sequence as the applied voltage increases.