Structural dependency of the optical properties of coupled GaAs quantum qots and rings

By using droplet epitaxy, we fabricated asymmetrically-coupled GaAs quantum dot molecules (AQDMs) and symmetrically-coupled GaAs concentric quantum-double rings (SCQRs). The geometrical coupling distances, dot-to-dot for the AQDMs and ring-to-ring for the SCQRs, were 30 nm and 28 nm, respectively. The photoluminescence (PL) measurement was performed with a femtosecond laser as an excitation source to investigate the structure-dependent optical properties of the AQDMs and the SCQRs as functions of the excitation intensity (corresponding to the injection carrier density). The excitation-power-dependent PL showed that the emission peak of the AQDMs was systemically red-shifted with increasing excitation intensity while the emission peak of the SCQRs was blue-shifted. The anomalous behavior in the shift of the emission peak for the AQDMs can be explained by using the inhomogeneous carrier distribution due to the geometrical asymmetry of the coupled QDs.