Optical transitions in quantum ring complexes

TL;DR

This paper reports the fabrication and analysis of nanometer-sized quantum ring complexes with variable geometry, revealing quantized electronic states through micro-photoluminescence and theoretical modeling.

Contribution

It introduces a droplet-epitaxial growth method for quantum rings with tunable geometry and provides experimental and theoretical insights into their electronic structure.

Findings

Discrete resonance lines indicate quantized electronic states.

Carrier confinement in inner and outer rings is distinctly observed.

Highly efficient photoluminescence from single quantum structures.

Abstract

Making use of a droplet-epitaxial technique, we realize nanometer-sized quantum ring complexes, consisting of a well-defined inner ring and an outer ring. Electronic structure inherent in the unique quantum system is analyzed using a micro-photoluminescence technique. One advantage of our growth method is that it presents the possibility of varying the ring geometry. Two samples are prepared and studied: a single-wall ring and a concentric double-ring. For both samples, highly efficient photoluminescence emitted from a single quantum structure is detected. The spectra show discrete resonance lines, which reflect the quantized nature of the ring-type electronic states. In the concentric double--ring, the carrier confinement in the inner ring and that in the outer ring are identified distinctly as split lines. The observed spectra are interpreted on the basis of single electron effective mass calculations.