Enhanced photoluminescence of colloidal nanocrystals embedded in epitaxially grown semiconductor microstructures

Abstract

Colloidal nanocrystals (NCs) integrated in epitaxially grown semiconductors provide a flexible alternative to Stranski-Krastanow quantum dots for many different optoelectronic applications such as low-threshold lasers or single-photon emitters. We studied the optical properties of various CdSe core-only and core/shell NCs integrated in ZnSe epitaxial-chemical hybrid structures. Depending on the type and environment of the NCs, a blueshift of the photoluminescence energy and a strong reduction of the emission intensity are observed after overgrowth. We demonstrate that these effects are caused by a potential barrier at the interface between NCs and ZnSe. The application of an appropriate postgrowth laser annealing procedure removes this potential barrier and enhances charge transfer from the ZnSe into the NCs. Consequently, we observe a significant increase of the emission intensity and a redshift of the photoluminescence energy of the NCs after annealing. Three-dimensional quantum-mechanical model calculations of the band diagram of the NCs as synthesized in solution, after overgrowth with ZnSe and after laser annealing confirm the presence of this potential barrier and its reduction due to the annealing.