First-principles and experimental characterization of the electronic and opticalproperties of CaS and CaO

Poncé, Samuel [UCL] Bertrand, Bruno Smet , P.F. Poelman, D. Mikami, M. Gonze, Xavier [UCL]

Doped alkaline-earth chalcogenides are interesting photoluminescen tmaterials for opto-electronic appli- cations. It is crucial to have an extended knowledge about the undoped bulk CaS and CaO since all the excited state properties of the doped material heavily dep end on it. In this work we investigate the struc- tural parameters, electronic band structures, macroscopic dielectric constants and absorption spectra for CaS and CaO compounds. Their quasi-particle band structure in the GW approximation yields a value of 4.28 eV and 6.02 eV for the indirect theoretical particle gap of CaS and CaO, respectively .The imaginary part of the macroscopic dielectric function e(x) is computed including excitonic effects through the Bethe–Salpeter equ ation. The onset of absorption is within 0.1 eV of the experimental one and the calcu- lated spectrum shows a qualitative agreement with experimen t. Our computed exciton binding energies are 0.27 eV and 0.40 eV for CaS and CaO, respectively.