Optical and spin coherence of excitons in zinc-blende GaN

The carrier recombination processes and the relaxation dynamics of spin-polarized excitons in cubic epitaxial GaN have been investigated by time-resolved photoluminescence and pump-probe spectroscopy experiments. We evidence a very fast exciton spin relaxation tau(S)similar to 0.3 ps that is influenced by both the high defect concentration and the strong electron-hole exchange interaction. Spectral oscillatory features of the transient reflectivity are observed for negative delays that allow us to determine the exciton optical dephasing time T-2.