Quadexciton cascade and fine-structure splitting of the triexciton in a single quantum dot

¹ Faculty of Physics, University of Warsaw - ul. Pasteura 5, 02-093 Warszawa, Poland
² Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA 25, avenue des Martyrs, 38042 Grenoble, France

Received: 12 October 2015
Accepted: 6 January 2016

Abstract

We report on the properties of emission lines associated with the cascaded recombination of a quadexciton in single GaAlAs/AlAs quantum dots, studied by means of polarization-resolved photoluminescence and single-photon correlation experiments. It is found that photons which are emitted in a double-step 4X-3X process preserve their linear polarization, similarly to the case of conserved polarization of correlated photons in the 2X-X cascade. In contrast, an emission of either co-linear or cross-linear pairs of photons is observed for the 3X-2X cascade. Each emission line associated with the quadexciton cascade shows doublet structure in the polarization-resolved photoluminescence experiment. The maximum splitting is seen when the polarization axis is chosen along and perpendicular to the [110] crystallographic direction. This effect is ascribed to the fine-structure splitting of the exciton and triexciton states in the presence of an anisotropic confining potential of a dot. We also show that the splitting in the triexciton state surpasses that in the exciton state by a factor up to eight and their ratio scales with the energy distance between the 3X and X emission lines, thus, very likely, with a lateral size and/or a composition of the dot.