Birefringence and band structure of CdP2 crystals

Abstract

The spatial dispersion in CdP2 crystals was investigated. The dispersion is positive (nk||с>nk||у) at λ>λ0 and negative (nk||с<nk||у) at λ<λ0. CdP2 crystals are isotropic for wavelength λо=896nm. Indirect transitions in excitonic region Еgx are nonpolarized due to one pair of bands. Minimal direct energy intervals correspond to transitions Г1→Г1 for Е||с and Г2→Г1 for Е⊥с. The temperature coefficient of energy gap sifting in the case of temperature changing between 2 and 4.2K equals to 10.6meV/K and 3.2mev/K for Г1→Г1 and Г2→Г1 band gap correspondingly. Reflectivity spectra were measured for energy interval 1.5–10eV and optical functions (n, k, ε1, ε2, d2ε1/dE2 and d2ε2/dE2) were calculated by using Kramers–Kronig analyses. All features were interpreted as optical transitions on the basis of both theoretical calculations of band structure.