Correlation between microstructure and electrical, optical properties of thermal annealed ITO thin films

Indium tin oxide (ITO) thin films with the thickness of 300 nm were deposited on quartz substrates via electron beam evaporation. Five samples were post-annealed in air atmosphere for 10 min at five selected temperature points from 200 to 600 °C, respectively. X-ray diffractometer, Hall measurement system and UV–Vis spectrophotometer were adopted to characterize the ITO thin films. Influence of thermal annealing in air atmosphere on microstructure was investigated. Furthermore, the correlation between microstructure and electrical, optical properties of ITO thin films was discussed in detail. All of the ITO thin films had a polycrystalline structure and a preferred orientation of (222), no matter annealed or not. The intensity ratio of I₍₂₂₂₎/I₍₄₄₀₎ initially increased and then decreased, it reached the maximum of 7.37 after annealed at 400 °C for 10 min. The lattice expansion evidently reduced after annealed at 300 °C or even higher temperature. The variation of mean grain size was minor during thermal annealing process regardless of annealing temperature. The carrier concentration is predominant in electrical conductivity, and it is dependent on the activation of donors and the density of oxygen vacancies. Hall mobility is strongly dependent on the mean grain size, lattice distortion and defect density. The optical transmittance is influenced by the density of oxygen vacancies and the consistency of grain orientations.