Optical and electrical properties of sol deposited fluorine-doped tin oxide (SnO ₂:F) thin films

Transparent, conducting thin films of fluorine doped tin oxide (SnO2:F) having various thickness were deposited by wet chemical technique using tin chloride (SnCl ₂ ·2H ₂O) and hydrogen fluoride (HF) as tin and fluorine containing precursors respectively, onto soda-lime glass substrate. Pure SnO ₂ is either an insulator or intrinsic semiconductor showing very high resistivity. Resistivity of SnO2 was reduced by fluorine (F) doping and annealing. The films thus obtained were subjected to microstructural, X-ray diffraction (XRD), optical and Fourier Transform Infrared Spectroscopy (FTIR) studies. XRD indicated tetragonal SnO ₂ crystallite. All the F doped films had transmittance >70% in the visible range. The bandgap was found to decrease from 3.79 eV to 3.72 eV with increase in thickness. The refractive indexes of the films were between 1.70 and 1.74. The electrical measurement of SnO2:F films having different thickness suggested a n-type conductivity, with the Hall mobility varying between 2.78 and 7.13 cm ²/V · s, whereas the carrier concentration varied from 6.75×10 ²⁰ cm ³ to 2097×10 ²⁰ cm ^-3. The sheet resistance of the samples decreased from 64 to 20 Ω/cm with increasing thickness.