Optical properties of ZnSe and its modeling

Spectral data for a ZnSe film grown on GaAs(100) are obtained at room temperature by spectroscopic ellipsometry (SE) in the photon energy range between 1.5 eV and 6 eV in steps of 5 meV. The optical dielectric function for bulk ZnSe is successfully extracted from the spectral data utilizing a multilayer analysis. The resultant data are better than previous data in that (1) the real part of the dielectric function below the band gap decreases smoothly following closely Marple's data obtained by the beam deviation method, which is more reliable than SE in this energy range, (2) the data reveal four distinctive critical point structures at E(0), E(0) + Delta(0), E(1), and E(1) + Delta(1), as is expected from the band structure, and (3) the maximum value of the imaginary part of the dielectric function in the E(1) region is highest among the reported data. The resultant data are expressed as a function of critical-point parameters and photon energies using our model, which is more generally valid than other models. This enables us to calculate the optical dielectric function not only over the entire photon energy range of the given spectral data, but also below and somewhat above the given spectral range. The excitonic effects apparently present in the spectral data are incorporated in our model. This enables us to determine excitonic parameters. The excitonic binding energy at Eo is found to be 13 meV at room temperature.