Analysis of dispersive optical constant of as deposited and annealed SnO2 thin films
Films of SnO2 were prepared by the spray pyrolysis technique onto glass substrate heated up to 500°C. Optical absorption measurements in the wavelength range 300-900 nm were studied and confirmed that annealing films at 550oC for different annealing time has a significant effect on the optical properties of the films. The optical constants confirmthat SnO2 films have an indirect band gap that decreased from3.3 to 3.1eV as the annealing time increases to 3hrs. The dispersion of the refractive index was analyzed using the concept of a single oscillator. The values of the single oscillator energy Eo were 6.6, 6.57, 6.48 and 6.18eV, while the dispersion energy Ed valueswere 94, 82, 77, and 70 for the as deposited and the annealed films for 1, 2, and 3hrs respectively. The increase in the density of localized states Eu from595 to 667meVcauses an expanding in theUrbach tail and consequently decreases the energy gap.