Optical constants of Cu(In 0.7Ga 0.3) 5Se 8 and Cu(In 0.4Ga 0.6) 5Se 8 crystals

Abstract

Variable angle spectroscopic ellipsometry has been applied to characterize the optical constants of bulk Cu(In 0.7Ga 0.3) 5Se 8 and Cu(In 0.4Ga 0.6) 5Se 8 crystals grown by the Bridgman method. The spectra were measured at room temperature over the energy range 0.8–4.4 eV. Adachi’s model was used to calculate the dielectric functions as well as the spectral dependence of complex refractive index, absorption coefficient, and normal-incidence reflectivity. The calculated data are in good agreement with the experimental ones over the entire range of photon energies. The parameters such as strength, threshold energy, and broadening, corresponding to the E 0, E 1A, and E 1B interband transitions, have been determined using the simulated annealing algorithm.