Optical properties of SnO 2 thin films grown by atmospheric pressure chemical vapour deposition oxiding SnCl 4

Abstract

Tin oxide thin films were grown by chemical vapour deposition (CVD) on glass substrates at atmospheric pressure (AP) and temperatures varying between 350 and 520 °C. A vertical home-made reactor was used for the deposition from SnCl 4 vapours with ambient air as oxidizer. Optical transmission measurements of these films were taken in the spectral range 200–2000 nm, and were analysed with the aid of the physical model introduced by Forouhi and Bloomer describing the optical dispersion in amorphous dielectrics ( A. Foroubi and I. Bloomer, Phys. Rev. B, 34 (1986) 7018 ). It was found that the model describes well the optical properties of APCVD SnO 2 thin films. The structure and the composition of the films changed with the deposition temperature and these changes implied modifications in the optical and electrical properties. Hence, the increase in the deposition temperature was found to imply an increase in the energy distance between bonding and antibonding states and a decrease in the energy band gap, as defined by the physical model. Energy states were found to appear within the energy gap as the deposition temperature increased. These states were related to the enhanced film conductivities.