Thin-capping-and-regrowth molecular beam epitaxial technique for quantum dots and quantum-dot molecules

Abstract

A thin-capping-and-regrowth molecular beam epitaxial technique is proposed and demonstrated to be a suitable approach for the growth of lateral quantum-dot molecules (QDMs). By regrowing on top of nanoholes, previously formed from as-grown quantum dots (QDs) via a thin-capping process, nanopropeller QDs are formed. By repeating the thin-capping-and-regrowth process for several cycles at the regrown thickness of 0.6 ML, nanopropeller QDs are linked along the [11¯0] crystallographic direction, leading to the alignment of QDs. The thin-capping-and-regrowth process is repeated for 1, 3, 5, 7, and 10cycles on different samples for comparison purposes. It is found from ex situ atomic force microscopy that at 7cycles of thin capping and regrowth of QDs, the best alignment of QDs is achieved. This is due to the strain having an optimum condition. The samples that undergo three and five thin-capping-and-regrowth cycles show some randomness of QD formation. When the process is repeated for 10cycles⁠, QDs become randomly distributed, but with a higher dot density than the as-grown sample. The high dot density results in a strong photoluminescence at room temperature. It is also shown that when self-aligned QDs are used as templates, aligned QDMs can be obtained at a regrowth thickness of 1.2 ML.