Optical functions and electronic structure of CuInSe2, CuGaSe2, CuInS2, and CuGaS2

摘要

We report on the complex dielectric tensor components of four chalcopyritesemiconductors in the optical energy range (1.4-5.2 eV, from 0.9 eV forCuInSe2) determined at room temperature by spectroscopic ellipsometry. Ourresults were obtained on single crystals of CuInSe2, CuGaSe2, CuInS2, andCuGaS2. Values of refractive indices n, extinction coefficients k andnormal-incidence reflectivity R in the two different polarizations are givenand compared with earlier data where available. We analyze in detail thestructures of the dielectric function observed in the studied energy region.Critical-point parameters of electronic transitions are obtained from fittingof numerically calculated second-derivative spectra. Experimental energies andpolarizations are discussed on the basis of published band structurecalculations.