Effects of tin on IR reflectivity, thermal emissivity, Hall mobility and plasma wavelength of sol-gel indium tin oxide films on glass

Sol-gel indium tin oxide films (ITO) of various composition (In:Sn atomic ratio = 90: 10 to 30:70) prepared from salt-based precursors were deposited on bare and SiO2 coated (similar to200 nm thickness) sheet glass substrates. The films were cured in air and then annealed under N-2/HO at similar to500degreesC to obtain ITO films of thickness 250-320 nm. Directional hemispherical reflectance (R-h) and trasmittance (T-h) of the films were measured in the wavelength range 0.25-18 mum. The reflectance of the films at 10 mum (near the peak wavelength of black body radiation) was in the range 0.18-0.55. The thermal emissivity (epsilon(d)) was evaluated from the relation: epsilon(d) = 1 - R-h - T-h (T-h approximate to 0, for sheet glass in the wavelength range 5 - 18 mum) and it was in the range 0.47-0.90. Reflectance (R-h) was also evaluated from measured sheet resistance values (R-square), from the relation R-h =(1 + 2epsilon(0)c(0)R(square))(-2), where epsilon(0) and c(0) are the permittivity of electron in vacuum and velocity of light, respectively. Specific resistivity of the films, measured by van-der Pauw method at ambient temperature was in the range 1.7 +/- 0.3 x 10(-3) to 6.6 +/- 1.2 x 10-3 0 cm. The sheet resistance (R-square) of the films was in the range 68-212 Omega/square. Free electron carrier concentration (N) and Hall mobility (mu) of the films were in the ranges (0.66 +/- 0.18) x 10(20) to (3.7 +/- 1.0) x 10(20) cm(-3) and (4.4 +/- 1.5) to (20 +/- 5) cm(2)/V s, respectively. These values were utilized to evaluate plasma wavelength (lambda(p)) of the conducting films which were in the range 1.72 +/- 0.24-4.07 +/- 0.58 mum. Considerable variations of the above properties were observed with increasing Sn content but minimum thermal emissivity and maximum IR reflectivity were observed in the case of In: Sn = 70:30. (C) 2002 Elsevier Science B.V. All rights reserved.