Facile synthesis and characterization of CdS thin films doped by yttrium atoms

Abstract

A facile preparation and structural, optical and electrical characterization of undoped and Y-doped CdS thin films are demonstrated through spray pyrolysis changing doping concentration of yttrium atoms in CdS structure. X-ray diffraction pattern displays that CdS samples have polycrystalline hexagonal phase and as they are doped by various amounts of Y atoms, a fluctuation is observed in the preferential orientation. Scanning electron microscopy results show that compact and smooth surface morphology in addition to a slight reduction in grain size are obtained with increasing Y-doping up to 5%. Transparency of CdS thin films are noticeably enhanced by doping of 1% Y atoms. However, further increase of Y-doping towards 5% causes less transparent CdS films due to deterioration of crystal quality. Tauc analysis indicates presence of two direct bandgaps for each sample owing to spin-orbit splitting of valence band of CdS. CdS films have bandgaps of 2.48 eV (E-g1) and 2.85 eV (E-g2). Whereas E-g1 value decreases to 2.46 for 5% Y-doping, E-g2 value increases to 2.92 eV for the same Y-doping concentration. Photoluminescence data show that an obvious red shift is observed for blue band regardless of Y-doping concentration. 3% Y-doped CdS thin films display the best carrier density of 4.37 x 10(14) cm(-3) and resistivity of 3.78 x 10(3) & omega;.cm, which originate from substitutional incorporation of Y3+ ions at Cd2+ ions. Therefore, it can be stated that Y-doped CdS thin films exhibit better electrical and optical properties that are of vital importance in thin film-based solar cells as a window layer.