OPTICAL-PROPERTIES OF ZNSE

We have studied the optical response of ZnSe in the 1.5-5.3-eV photon-energy range at room temperature by spectroscopic ellipsometry. The measured dielectric-function spectra reveal distinct structures at energies of the E0, E0 + DELTA-0, E1, and E1 + DELTA-1 critical points (CP's). These data are analyzed on the basis of a simplified model of the interband transitions. The E0-(E0 + DELTA-0) structures are characterized by a three-dimensional M0 CP, the E1-(E1 + DELTA-1) structures by a two-dimensional M0 CP, and the E2 structure by a classical Lorentzian oscillator (damped harmonic oscillator). The experimental data could not be explained within the framework of the one-electron approximation, since excitonic effects may profoundly modify the CP singularity structure. The model is thus made to account for the excitonic effects at these CP's; our results are in satisfactory agreement with the experiment over the entire range of photon energies. Dielectric-function-related optical constants of ZnSe, such as the refractive index, the extinction coefficient, and the absorption coefficient, are also presented and analyzed.