Effect of solvent ratio on the properties of highly oriented sprayed fluorine-doped tin oxide thin films

摘要

Transparent conducting thin films of F:SnO_2 have been deposited onto preheated glass substrates by a spray pyrolysis technique using pentahydrate stannic chloride (SnCl_4·5H_2O) and ammonium fluoride (NH_4F) as precursors and mixture of water and propane-2-ol as solvent. The concentration of SnCl_4·5H_2O and NH_4F is kept fixed and the ratio of water and propane-2-ol solvent in the spraying solution is varied. A fine spray of the source solution using air as a carrier gas has grown films of thickness up to 995 nm. Optical absorption, X-ray diffraction, Van der Pauw technique for measurement of a sheet resistance and Hall effect measurements at room temperature for determination of carrier density and conductivity have been used. The as-deposited films are of polycrystalline SnO_2 with a tetragonal crystal structure and are preferentially having orientation along the (200) direction with texture coefficient as high as 6.16. The average grain size for the as-deposited sample is found to be of the order of 44 nm. The films have moderate optical transmission (up to 70-85% at 550 nm). The figure of merit (φ) values vary from 1.95 · 10~(-3) to 35.68 · 10~(-3) Ω~(-1). The films are heavily doped, degenerate and exhibit n-type electrical conductivity. The lowest sheet resistance (R_s) for the optimized sample is 5.1 Ω. The films have a resistivity of 5.43 · 10~(-4) Ω cm and mobility around 7.38 cm~2 V~(-1) s~(-1).