Charge control in laterally coupled double quantum dots

We investigate the electronic and optical properties of InAs double quantum dots grown on GaAs $\left(001\right)$ and laterally aligned along the $\left[110\right]$ crystal direction. The emission spectrum has been investigated as a function of a lateral electric field applied along the quantum dot pair mutual axis. The number of confined electrons can be controlled with the external bias, leading to sharp energy shifts which we use to identify the emission from neutral and charged exciton complexes. Quantum tunneling of these electrons is proposed to explain the reversed ordering of the trion emission lines as compared to that of excitons in our system.

Figure 1

(Color online) (a), (b), and (c) show two AFM images and an optical image of a single QD pair, a 1.5-$\mu$m-wide GaAs channel, and a full MSM device, respectively. (d)–(f) show contour maps of the bias-dependent $\mu$-PL measured in four different nanostructures. The orange (spotted) lines stand for the $\mu$-PL intensity integrated in the corresponding emission ranges.

Figure 2

(Color online) (a) Electric field vs bias dependence calculated using a semianalytical transport model (black solid line). Spectrally integrated $\mu$-PL intensity obtained in the same bias range [orange (spotted) line]. (b) $\mu$-PL contour plot map vs lateral bias measured for QN1. The inset compares the experimental (left-hand side) and theoretical (right-hand side) emission energies for lines P1–P4. (c) Two spectra extracted from the contour plot at the indicated voltages. (d) Excitation power evolution of P1–P4 and corresponding Lorentzian fits (solid lines).

Figure 3

(Color online) (a) $\mu$-PL contour plot map vs lateral bias measured for QN2. (b) Comparison between experimental (left-hand side) and theoretical (right-hand side) energies for $X^0$ and $X^{-}$ emission from QD A and B ($d=30$ nm).

Figure 4

(Color online) Calculated energy of the negative trions (a), electrons (b), and corresponding trion emission line (c) as a function of the interdot distance $d$. The insets indicate the location of electrons and holes in the long $d$ limit. $E_g$ is the gap energy.