Near-field optical observation of electric-field-induced fluorescence switching in laterally coupled quantum dots

We report on direct observation of spatial and optical luminescence switching (on and off condition) due to collapse of the coupling conditions of quantum dots (QDs) pair. In particular, one could observe that the relative intensities between two adjacent luminescence peaks and spatial images of individual QDs located closely nearby in a high-density self-assembled QD structure underwent a reversible change with respect to an external electric field.

Figure 1

(Color online) (a) AFM image of InGaAs QDs without GaAs capping layer (left) and the enlarged area of closely located QDs (right). (b) The lateral size distribution (red dots) and Gaussian fitting (broken red line) of QDs obtained from (a) while compared with the high-resolution PL spectrum (solid line). (c) Scanning electron micrographic image of the etched axicon lens probe.

Figure 2

(Color online) (a) PL spectra that show the reverse intensity change and energy shift of the PL peaks A and B with increasing the electric field unlike PL peaks C–G. (b) PL spectra that show the continuously intensity decreasing and unchange of energy with increasing the electric field. (c) Photon energy shift of PL peaks A–G under applying electric field of (a).

Figure 3

(Color online) [(a)–(e)] Fitted PL peaks of Fig. 2a for obtaining intensity change in the PL peaks A (blue line) and B (red line) under the electric field variation without intensity supporting of background signal. (f) The intensity variation in A (blue dot) and B (red dot) of (a)–(e) as a function of applied electric field. (g) The corresponding spatial PL-intensity images for the respective PL energies of (1)–(10) in Fig. 2a. The crosses in (2), (4) and (7), (9) represent the center of the PL intensity images of (6), (8), (10) and (1), (3), (5), respectively. (h) The corresponding spatial profiles of (5) and (6) in the $x$ and $y$ directions of (g) are presented, respectively.

Figure 4

(Color online) (a) Calculated contour plot of the potential of the induced lateral electric field between QDs located closely nearby. The vertical electric field along the $z$ direction is also shown. (b) Vector plot of the laterally induced electric-field components in the center area of two QDs. (c) Cross-sectional profile of the electric field along the $x$ axis of (b) with respect to the distance between QDs A and B at 2, 4, and 6 nm growth direction. Here the positive (negative) electric field denotes the field direction in the positive (negative) $x$ direction of (a) and (b). (d) Sketch of the lateral QD potential structure for the coupled condition as well as the collapse condition with respect to the critical external electric field $\left(E_C\right)$.