Résumé
By performing non-degenerate pump-probe experiments, we study the relaxation dynamics of spin-polarized A and B excitons in wurtzite epitaxial GaN. By analyzing the differential reflection of the two circularly polarized probe components, we extract characteristic times of the different spin relaxation processes. We show that the spin relaxation of the exciton as a whole is negligible in regard to the spin relaxation of the individual carriers. We determined T-e = 15 ps for the electron in the conduction band, T-hh = 5 ps, and T-lh = 1.5 ps for the heavy hole and for the light hole, respectively. The quite long HH relaxation time can be related to the band structure in which the degeneracy between different spin valence bands is lifted.