Collinear Polarization of Exciton/Biexciton Photoluminescence from Single Hexagonal GaN Quantum Dots

We report a collinear, strong polarization of exciton and biexciton emission from single GaN quantum dots. Polarization-dependent micro-photoluminescence spectroscopy was performed on single dots. The Stokes polarization vectors of exciton and biexciton lines face in the same direction, with a different linear polarization angle for each dot. A model in which a strong linear polarization is caused by shape anisotropy alone without considering exchange interaction can explain our findings. This is the first experimental observation of collinear polarization for an exciton and a biexciton from the same GaN quantum dot.