The growth and characterization of long chains of InAs quantum dot molecules

InAs quantum dot molecules (QDMs) are obtained from quantum dot (QD) overgrowth on nanopropeller templates which are grown by thin-capping-and-regrowth molecular beam epitaxy (MBE) process. The template structure is elongated along [110] crystallographic direction with QDs at the centre. They were used to grow QDMs aligned in that direction. Multi-cycles of thin-capping-and-regrowth with appropriate thin-capping thickness were investigated in order to create long nanopropeller templates. They are used as templates for the growth of long chain quantum dot molecules. By overgrowth of additional QDs in the final cycle of thin-capping-and-regrowth, satellite QDs are created on nanopropeller blades. With proper overgrowth thickness, long chain QDMs are successfully created on long nanopropeller templates. Lateral alignment of long chain QDMs contribute to anisotropic coupling among QDs. They lead to different magnitudes of wave vectors between [110] and [110] directions in the energy band structure of QDs ensembles. Hence, long chain QDMs demonstrate anisotropy of optical property, i.e. polarization dependence of PL spectrum, while as-grown QDs and small-group QDMs do not exhibit this property. The polarization degree of optical property agrees with the length of QDMs and their templates. However high QD density limits the anisotropic property due to increased QD coupling along the [110] direction.