Optical constants of ε-GaSe

Abstract

The optical response of ε-GaSe for light polarization perpendicular to the c-axis in the 2.0-5.0-eV photon-energy range has been studied at room temperature by spectroscopic ellipsometry. The measured dielectric-function spectra reveal distinct structures at energies of the E1 (∼3.6 eV) and E3 (∼4.9 eV) critical points (CPs). The experimental data are analyzed on the basis of a simplified model of the interband transitions. The E1 structure is characterized by a two-dimensional (2D) M 0 CP plus 2D discrete exciton, and the E3 structure is assumed to act as a damped harmonic oscillator. Results are in satisfactory agreement with the experiment over the entire range of photon energies.