  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
di erence (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 di erence seen for the exciton, a fact that
may be attributed to a possible change in the selection rules for the lowered
symmetry.
