Electronic structure of p-type ultraviolet-transparent conducting CUScO2 films

We investigate the electronic structure of CuSCO2 thin films grown on sapphire and mica substrates by pulsed laser deposition. X-ray diffraction and microanalysis confirm that the films have the expected delafossite crystal structure and stoichiometric proportions. The electronic structure is investigated by means of X-ray and ultraviolet photoelectron spectroscopy. Electronic states in the range 0-1350 eV are identified, making reference to theoretical density-of-states calculations up to 80 eV Photoelectron spectra near the Fermi energy confirm the p-character of the films. Optical absorption spectroscopy shows that the films are transparent up to 3.7 eV and exhibit an intense excitonic peak, with a direct gap energy of 4.24 +/- 0.05 eV at room temperature. Ab initio band structure calculations confirm the direct character of CUSCO2 and allow for an assignment of the direct gap to an electronic transition at the L point of the rhombohedral Brillouin zone. (C) 2007 Elsevier B.V. All rights reserved.