Low-Density Quantum Dot Molecules by Selective Etching Using in Droplet as a Mask

We demonstrate low-density quantum dot molecules (QDMs) by selective etching using In droplets as a mask. Selective etching is performed with InGaAs QDMs buried underneath GaAs capping layer, on which In droplets are formed by droplet epitaxy using molecular beam epitaxy. During the chemical etching, the droplets act as a mask and QDMs underneath the droplets that only survive. Photoluminescence measurement from the selectively etched QDMs in mesa structures shows a much reduced intensity, which indicates low-density QDMs. This technique provides a simple and flexible method to attain low-density QDMs. The density can be easily modified by the control of the size and density of In droplets, which is suitable for single QDM spectroscopy and for their device applications.