Optical characterization of CuIn_3Se_5, CuGa_3Se_5 and CuGa_5Se_8 crystals by spectroscopic ellipsometry

摘要

The ellipsometric spectra of CuIn_3Se_5, CuGa_3Se_5 and CuGa_5Se_8 ordered vacancy compounds (OVC) have been studied in the spectral range from 0.8 to 4.4 eV. The structures observed in the measured spectra were analyzed by fitting the second derivative of the experimental spectrum to analytical line shapes. The energies corresponding to different electronic transitions were determined. The lowest direct gap (E_0) is characterized by 3-dimensional critical points, while higher energy structures are characterized by 2D critical points. Optical constants related to dielectric function, such as the complex refractive index n~* (ω), extinction coefficient k(ω), absorption coefficient α(ω), and normal-incidence reflectivity R(ω), of studied OVC were determined.