Study of sol-gel-derived high tin content indium tin oxide (ITO) films on silica-coated soda lime silica glass

Sol-gel indium tin oxide films (ITO) of different thickness (120 +/- 25 - 40 to 560 +/- 25 - 40 nm) and of various compositions (In:Sn = 90:10, 70:30 and 50:50) prepared from In metal and Sri salt were deposited on silica-coated ( - 200 rim thickness) sheet glass substrate by the spinning technique. The films were cured in reducing atmosphere (N-2 + H2O vapour) at 500 +/- 5 degreesC, and these were of bixbyite-type structure with cubic In2O3 phase. Directional hemispherical reflectance (Rh) and transmittance (T-h) of the films were measured in the wavelength range 0.25-18 mum. The Rh in the IR region was found to be maximum ( similar to0.62 at 10 mum) for In:Sn=70:30 resulting in minimum thermal emissivity (epsilon(d) = 0.36). The thermal emissivity (epsilon(d)) was evaluated from the relation, epsilon(d) = 1 - Rh - Th (Th = 0 for sheet glass in the wavelength range 5-18 mum), and it was in the range 0.36-0.85. The achieved sheet resistance of the films was in the range 55-1700 Omega/square. Resistivity of the films of relatively low sheet resistance measured by van der Pauw method at ambient temperature was in the range (1.4 +/- 0.2) x 10(-3) to (3.5 +/- 0.6) x 10(-3) Omega cm, and it was minimum for In:Sn = 70:30 which resulted in maximum carrier concentration. Free electron carrier concentration (N) and Hall mobility (mu) of the films were in the range (1.4 +/- 0.4) x 10(20) to (4.8 +/- 1.3) x 10(20) cm(-3) and (9.5 +/- 2.4) to (13 +/- 3) cm(2)/V s, respectively. The Hall mobility of the films passes through minima with an increase in tin content. (C) 2003 Elsevier B.V. All rights reserved.