Optical properties of chalcopyrite CuAlxIn1−xSe2 alloys

Abstract

We report pseudodielectric functions 〈ε〉 of the quaternary semiconductor alloys CuAlxIn1−xSe2. Measurements were done in polycrystalline samples from 0.7 to 5.1 eV at room temperature by spectral ellipsometry. Accurate values of refractive indices n and extinction coefficients k representative of the bulk materials are reported. The dependence on composition of the reflectivity at normal incidence R(x) at the He–Ne laser wavelength λ=1.523 μm provides an optical method to determine the composition of these alloys. The structures observed in 〈ε〉 are analyzed by fitting the numerically differentiated spectra of d2〈ε〉(ω)/dω2 to analytic line shapes. The obtained energies are related to given interband transitions by taking into account the electronic band structures of the ternary end-point compounds.