Evolution of Various Nanostructures and Preservation of Self-Assembled InAs Quantum Dots During GaAs Capping

The fabrication of nanostructures such as quantum rods (QRDs), quantum dot pairs (QDPs), bridged QDPs, and dimpled QDs (DQDs) is achieved by an application of a shallow GaAs layer using solid source molecular beam epitaxy (MBE). More specifically, the shape transition and evolution process as well as the preservation of original dome shape of self-assembled InAs quantum dots (QDs) are studied during the thin capping of GaAs layers in terms of morphology and optical property. As QDs are required to be capped for their applications and optical characterizations, it is critical to understand the mechanism during the capping process. QDs go through a significant shape transition and eventually evolve into various nanostructures at temperatures between 500°C and 400°C, while the original dome shape can be maintained at temperatures below 360°C. The shape evolutions are mainly driven by diffusion process induced by redistribution of surface chemical potential and strain matrix. Photoluminescence (PL) results show a blue-shift with increasing capping temperature for a fixed capping thickness, which adequately matches with morphological evolution.