Optical functions and electronic structure of CuInSe<inf>2</inf>, CuGaSe<inf>2</inf>, CuInS<inf>2</inf>, and CuGaS<inf>2</inf>

We report on the complex dielectric tensor components of four chalcopyrite semiconductors in an optical energy range (1.4-5.2 eV, from 0.9 eV for CuInSe2) determined at room temperature by spectroscopic ellipsometry. Our results were obtained on single crystals of CuInSe2, CuGaSe2, CuInS2, and CuGaS2. Values of refractive indices n, extinction coefficients k, and normal-incidence reflectivity R in the two different polarizations are given and compared with earlier data where available. We analyze in detail the structures of the dielectric function observed in the studied energy region. Critical-point parameters of electronic transitions are obtained from a fitting of numerically calculated second-derivative spectra d2ε(ω)/dω2. Experimental energies and polarizations are discussed on the basis of published band-structure calculations. © 2001 The American Physical Society.