Hot phonon effects in ZnSe

Femtosecond pump-probe differential reflectivity spectroscopy is used to investigate the ultrafast cooling dynamics of hot photoexcited carriers in a high-quality ZnSe epilayer grown on GaAs. Comparison with a theoretical model based on a balance equation approach indicates that the observed reduction in the electron cooling rate with increasing carrier density (for carrier densities greater than ～3×10¹⁷cm^?3) is due to both screening of the Fröhlich interaction and a non-equilibrium hot longitudinal optic-phonon population generated by the cooling electron distribution.