Invited paper: Excitonic optical nonlinearities in ZnSe epitaxial films

Excitonic optical nonlinearities in epitaxial ZnSe thin films have been measured at 150 and 300K. The measured nonlinear response, Δn/N = 1.8×10⁻¹⁹ cm³ at 300K, is comparable to that observed in bulk GaAs and GaAs/AlGaAs multiple quantum well systems. Analysis of these results using our partly-phenomenological plasma theory indicates that the mechanisms responsible for this nonlinearity at room temperature are exciton screening and density-dependent broadening. At 150K, exciton screening makes the major contribution to the nonlinearity. Using femtosecond laser techniques, we have determined that the nonlinearity turns off in times on the order of 50-100 ps. These excitonic nonlinearities are, therefore, both large in magnitude and extremely rapid.