Optical constants and electronic energy-band structure of AgGaSe_2

摘要

The complex dielectric-function spectra, ε(E) = ε_1(E) + iε_2(E), of the AgGaSe_2 chalcopyrite semiconductor have been measured by spectroscopic ellipsometry (SE) for light polarizations perpendicular (E⊥ c) and parallel to the c-axis (E‖ c) in the 1.6-5.3eV photon-energy range at room temperature. The measured ε(E) spectra reveal distinct structures of critical points in the Brillouin zone. Analysis of the numerically derived ε(E) spectra facilitates the precise determination of critical-point energies. By performing the band-structure and dielectric-function calculations, these critical points are successfully assigned to specific points in the Brillouin zone. The dielectric-related optical constants of AgGaSe_2, such as the complex refractive index n~* = n + ik, the absorption coefficient α, and the normal-incidence reflectivity R, are presented.