  The optical orientation of the exciton spin in an ensemble of self-organized
cubic GaN/AlN quantum dots is studied by time-resolved photoluminescence. Under
a polarized quasi-resonant excitation, the luminescence linear polarization
exhibits no temporal decay, even at room temperature. This demonstrates the
robustness of the exciton spin polarization in these cubic nitride
nanostructures, with characteristic decay times longer than 10 ns.
