Effect of Antimony and Fluorine Doping on Electrical, Optical and Structural Properties of Tin Oxide Films Prepared by Spray Pyrolysis Method

Undoped, antimony doped and fluorine doped tin oxide films have been prepared by spray pyrolysis technique. The films were deposited on glass substrates at temperatures ranging between 300°C and 370°C by spraying an alcoholic solution of tin tetra chloride $(SnCl_4)$. Dopants used were antimony tri chloride $(SbCl_3)$ for antimony doped tin oxide (ATO) films, and ammonium fluoride $(NH_4F)$ for fluorine doped tin oxide (FTO) films. Among undoped tin oxide films, the least resistivity was found to be $3.1\times 10^{-3} \Omega-cm$ for a molar concentration of 0.75 M. In case of antimony doped films minimum resistivity value was found to be $7.7\times 10^{-4} \Omega-cm$ for a film with (Sb/Sn) = 0.065, deposited at 370°C and in case of fluorine doped films it was found to be $1.67\times 10^{-3}\Omega-cm$ for a doping percentage of 3 at% of fluorine in 0.1 M solution. The corresponding values of the carrier concentrations were found to be $1.8\times 10^{20}/cm^3$ and $9.98\times 10^{20}/cm^3$, respectively. The electrical and optical properties of these films were studied as a function of both doping concentration and substrate temperature. Doping percentage of antimony and fluorine in the spray solution has been optimized for achieving a minimum electrical resistivity. The dependence of electrical properties such as resistivity, carrier concentration and mobility of doped films were analyzed. Influence of antimony dopant on the optical band gap of the films has been reported on the basis of electron conduction mechanism. Air and argon annealing effects on the electrical properties of antimony doped tin oxide films were also studied