Effect of erbium on the structural, morphological, and optical properties of SnO₂ thin films deposited by spray pyrolysis

In the present work numerous compositions of Er-doped SnO₂ thin films were made at 425 °C on a quartz glass substrate using spray pyrolysis method. The powder X-ray diffraction and X-ray photoelectron spectroscopy analysis confirms the tetragonal phase and surface chemical composition of as made Sn_1-xEr_xO₂ (x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05) thin films. The grain size and RMS roughness of the films were estimated from the AFM measurements and the film surface has a saw-tooth-like morphology. The transmission spectra of the films are fallen in the visible range having between 60% and 80% transmittance with different Er concentration. The optical direct, indirect band gap and phonon energy values have been estimated. The photoluminescence measurements under excitation at 325 nm show three distinct emission peaks, a broad hump positioned at 390 nm, two sharp peaks at 420 nm related to tin interstitials, and a sharp peak at 700 nm related to oxygen vacancies. The Er³⁺ in SnO₂ increased the oxygen vacancies to maintain charge balance and as a result the intensity of emission peaks increases with Er content.