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

Abstract

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 Sn salt were deposited on silica-coated (∼200 nm thickness) sheet glass substrate by the spinning technique. The films were cured in reducing atmosphere (N 2+H 2O vapour) at 500±5 °C, and these were of bixbyite-type structure with cubic In 2O 3 phase. Directional hemispherical reflectance ( R h) and transmittance ( T h) of the films were measured in the wavelength range 0.25–18 μm. The R h in the IR region was found to be maximum (∼0.62 at 10 μm) for In:Sn=70:30 resulting in minimum thermal emissivity ( ε d=0.36). The thermal emissivity ( ε d) was evaluated from the relation, ε d=1− R h− T h ( T h≈0 for sheet glass in the wavelength range 5–18 μm), and it was in the range 0.36–0.85. The achieved sheet resistance of the films was in the range 55–1700 Ω/□. 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)×10 −3 to (3.5±0.6)×10 −3 Ω cm, and it was minimum for In:Sn=70:30 which resulted in maximum carrier concentration. Free electron carrier concentration ( N) and Hall mobility ( μ) of the films were in the range (1.4±0.4)×10 20 to (4.8±1.3)×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.