InAs quantum dot molecules on nanohole/cross-hatch pattern templates

Abstract

This thesis studies the evolution and characteristics of quantum dot molecules (QDMs) on cross hatch patterns (CHPs). QDMs are grown by a partial-capping-and-regrowth technique on CHP templates which are 25-nm In0.2Ga0.8As on GaAs substrates. The morphological and optical properties of the nanostructures are studied by atomic force microscope (AFM) and photoluminescence (PL), respectively. The morphologies of nanostructures on CHPs vary significantly depending on the areas and can be concluded as follows. On Flat areas, the nanostructures develop from nanoholes (NHs) to nanopropellars (NPs) and QDMs which are uniform and similar to those grown on flat GaAs substrates. On [110] misfit dislocation (MD) lines, the strain affects the symmetries of nanostructures, and some of them transform to new types of nanostructures: diamond-shaped NHs, diamond-based QDs, and NPs which resemble a quantum cellular automata (QCA) unit cell. On [1-10] MD lines, partial capping of GaAs creates NHs and stripes of nanomounds; the regrowth of InAs creates diamond-based QDs on the NHs, QDs on the edge of the stripes, and QDs on the ridge of the stripes PL measurements of QDMs on CHPs show that the entire structure strongly emits broad signals in the 0.89-1.6 eV range, indicating high crystalline quality. At high temperature, the effects of carrier migration from small QDs to large QDs are observed. The rich morphologies observed in this works may increase the range of useful optoelectronic materials and devices in the near infrared.