Control of the number of dots in inas quantum dot molecules for quantum computing

Self-assembled lateral InAs quantum dot molecules (QDMs) are grown by solid-source molecular beam epitaxy (MBE) technique using the thin-capping-and-regrowth MBE process. Thin-capping of GaAs on as-grown InAs quantum dots (QDs) at low temperatures leads to nanohole templates. The shape, size and depth of nanoholes are controlled by capping thickness. Subsequent regrowth with 0.6 ML of InAs on the templates result in nano-propeller QDs with different blades' dimensions. We found that the length of the propeller blades is controlled by either the capping temperature or the thickness of capping layer. When the amount of InAs regrowth layer increases from 0.6 to 1.2 and 1.5 ML, QDMs with different shapes are created. The center dots are formed by filling up nanoholes at the beginning phase until the strain relaxation at center becomes minimized. Later on, the rest of InAs regrowth material starts to form satellite dots along the blade of nano-propeller where remaining strain fields are still distributed at the perimeter of nano-propeller blades. The dot uniformity and their dot size of all QDM samples are examined by photoluminescence (PL) measurements at 77 K. Furthermore, the excitation power dependence of PL spectra of all samples is also conducted. The PL results from some case of different QDMs also exhibit the shift of the PL peaks toward higher energies. We believe that the coupling between center dot and satellite dots lead to the extending in their band structures.