Structural and optical investigation of spray-deposited SnO2 thin films

A study of the investigation of tin oxide (SnO2) thin films deposited by spray pyrolysis method was undertaken by analysing the structural and optical properties for different substrate temperatures. X-ray diffraction patterns have revealed that the formation of tetragonal tin oxide nanoparticles was observed and the crystallite size, strain and dislocation density of the samples vary with the substrate temperature. In addition, X-ray photoelectron spectroscopy was used to obtain the composition and electronic structure. From morphological characterization, it is clear that the thin films are uniform without cracks with dense morphology consisting homogenous distribution of crystallites in nanometer dimension. Analysis on optical properties revealed that the direct optical band gap of the SnO2 films lies between 3.88 and 3.98 eV up to the substrate temperature of 450 °C, and it showed a remarkable decrease to 3.73 eV for 500 °C. The envelope method analysis based on the use of the maxima and minima of the interference fringes has been used to define the complex index of refraction and the extinction coefficient. Photoluminescence characteristics of the SnO2 thin films were investigated at room temperature. The all photoluminescence spectra have exhibited six luminescence centres ascribed to the presence of intrinsic defects such as oxygen vacancies and structural defects in the SnO2. Two of them are for room-temperature radiative recombinations of band-acceptor and donor–acceptor pairs observed at 420 and 451 nm, respectively. All of the results have been appreciated for optoelectronic and sensor devices.