Dispersion of Principal Refractive Indices of CaGa2S4

Abstract

The wide-gap semiconductor, CaGa2S4, is already regarded as a promising host constituent in phosphor and laser materials. In this work the principal refractive indices of CaGa2S4, which is a biaxial material have been studied by conventional spectroscopic ellipsometry. The ellipsometric measurements have been carried out on (100), (010), and (001) crystal planes, with the aid of the multi-configuration method. The dispersion of the principal refractive indices, nx, ny, and nz, has been determined in a region of transparency of CaGa2S4 at energies below 4.0 eV. The relevance between the anisotropy of the obtained indices and that of the inter-band optical transitions in the absorption region has been vividly exposed by the critical point analysis of the εyy and εzz components of the dielectric function at energies above 4.0 eV. The nature of the optical transitions at and above the energy gap is discussed using available data on the band structure of CaGa2S4.