Picosecond photoinduced reflectivity studies of GaN prepared by lateral epitaxial overgrowth

The pump-probe technique has been used to perform room temperature studies of the photoinduced changes in the reflectivity DeltaR associated with exci ton and carrier dynamics in GaN prepared by lateral epitaxial overgrowth. F or resonant excitation of cold excitons, the DeltaR decay possesses a 720 p s component attributed to the free exciton lifetime in this high quality ma terial. For electrons with small excess energy (< 50 meV), the strong incre ase in the <Delta>R decay rate with decreasing excitation density suggests that screening of the Coulomb interaction may play an important role in the processes of carrier relaxation and exciton formation. The faster decay ti mes at a given carrier density observed for hot (> 100 meV) electron relaxa tion are attributed to electron-hole scattering in conjunction with the scr eened electron-LO phonon interaction.