Incorporation of transparent conducting oxide characteristics and oxygen analysis in vacuum annealed indium oxide films

Indium oxide films prepared by thermal oxidation of In metal films acquire high electrical conductivity and optical transmission on annealing in vacuum. These films, by virtue of their high figure of merit (1.3 × 103 Ω−1 cm−1), can function as transparent conducting oxides. Deposition of smooth In metal films is essential for realizing good figure of merit in oxide films. Roughness existing in metallic films persists in oxide films and impairs their properties, in particular, optical transmission. Analyses by Rutherford backscattering spectrometry and 16O(α,α)16O resonant scattering suggest that vacuum annealing brings about a subtle oxygen deficiency in films and also causes a reduction in their thicknesses. The deficiency of oxygen results from the loss of lattice oxygen and desorption of chemisorbed oxygen, and is responsible for the enhanced electrical conductivity of the films. The reduction in thickness, on the other hand, occurs due to the volatilization of In2O formed under the reducing environment of vacuum. X-ray photoelectron spectroscopy studies show that vacuum annealing renders films reactive towards oxygen bearing species. These films, as a result, tend to regain the nominal oxide composition on prolonged storage in ambient air, however, their TCO properties remain largely unaffected. The nature of oxygen absorbed in the process is seemingly different from that in air-annealed oxide films.