Identification of Optical Transitions by Spectroscopic Ellipsometry (SE) on CuIn<sub>3</sub>Se<sub>5</sub> Bulk Compounds

Abstract

Bulk materials were synthesized by the Bridgman technique using the elements Cu, In and Se. These samples were characterized by Energy Dispersive Spectrometry (EDS) to determine the elemental composition, as well as by X-ray diffraction for structure, hot point probe method for type of conductivity, Optical response (Photoconductivity) and Photoluminescence (PL) to determine the band gap value and Spectroscopic Ellipsometry to find energy levels above the gap in the band scheme at room-temperature. They show a nearly perfect stoechiometry and present a p-type conductivity. CuIn 3 Se 5 either has a Stannite structure, an Ordered Defect Chalcopyrite structure (ODC), or an Ordered Vacancy Chalcopyrite structure (OVC). The gap energy obtained for the different samples was 1.23 eV. Energy levels above the gap in the band scheme were determinate by measuring the dielectric function at room temperature for energies lying between 1.5 and 5.5 eV. Many transitions were observed above the gap for different samples. Spectroscopic Ellipsometry gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum.