Studies on properties of sprayed SnO2 thin films as a function of substrate-nozzle distance and substrate temperature

Transparent polycrystalline tin oxide (SnO2) thin films were deposited on commercial microscope glass substrates using spray pyrolysis method. Thin films were deposited at various nozzle-to-substrate distances from 20 to 40 cm in steps of 5 cm and at various substrate temperatures ranging between 380 to 440 degrees C in steps of 20 degrees C. The thin films are found to have a tetragonal rutile structure. Lattice parameters were calculated as a = 4.74 angstrom and c = 3.18 angstrom. The surface morphology of the films were imaged by SEM (Scanning Electron Microscope). The average grain size of the films obtained were 22.3-74.8 nm by using Scherrer's formula. The films were found to exhibit high transmittance >90 % in the visible regions. Absorption coefficient alpha and the thickness of the film t were calculated from interference of transmittance spectra. Refractive index n and extinction coefficient k were determined from transmittance spectrum in the ultraviolet-visible-near infrared regions using envelope methods. The refractive index is found to vary between 1.76-1.92 in the wavelength range of 4001100 nm. The values direct band gaps of the films obtained were 3.99-4.11 eV. The electrical resistivity (rho) of the films obtained were (2.47-7.13).10(-4) Omega cm by using Ohm's law