Asymmetry of localised states in a single quantum ring: Polarization dependence of excitons and biexcitons

We performed spectroscopic studies of a single GaAs quantum ring with an anisotropy in the rim height. The presence of an asymmetric localised state was suggested by the adiabatic potential. The asymmetry was investigated in terms of the polarization dependence of excitons and biexcitons, where a large energy difference (∼ 0.8 meV) in the exciton emission energy for perpendicular polarizations was observed and the oscillator strengths were also compared using the photoluminescence decay rate. For perpendicular polarizations, the biexciton exhibits twice the energy difference seen for the exciton, a fact that may be attributed to a possible change in the selection rules for the lowered symmetry.