Cross-sectional structures and conductive properties of ITO–Al<sub>2</sub>O<sub>3</sub> composite thin films prepared by aerosol deposition

Tin-doped indium oxide (ITO) thin films are used extensively, particularly in flat-panel displays and photovoltaic cells, because of their exceptional electrical conductivity and high visible-light transmittance. However, ITO is expensive because one of its components is In, which is a rare metal, making a stable supply of ITO difficult to attain. The objective of the present study was to reduce the use of In in ITO by combining it with Al2O3, which is relatively inexpensive and highly transparent, and exhibits high mechanical strength. The resulting ITO–Al2O3 composite thin films were fabricated by aerosol deposition. The resultant films exhibited a resistivity of 4 × 10−3 Ω cm and a visible-light transmittance of 87 % at a wavelength of 600 nm, which are similar to the values for ITO films deposited by the same AD method. The resistivity remained almost constant with increasing volume fraction of Al2O3 in the composite thin film until the volume fraction reached 66 %, beyond which a notable increase in resistivity was observed. An increase in the gas flow rate resulted in a reduction in resistivity, with a strong correlation observed between the resistivity and the crystallite size determined by the Williamson–Hall method. Elemental analysis of the cross-section of a composite thin film indicated the presence of In and Al. The distribution of In was found to become more widespread and denser with increasing gas flow rate, indicating densification of the film. The visible-light transmittance exhibited a minimal dependence on the Al2O3 volume fraction.