Photoconductivity in In2O3 nanoscale thin films: Interrelation with chemisorbed-type conductometric response towards oxygen

A systematic experimental study of the spectral and transient characteristics of the photoconductivity near the fundamental optical absorption edge of both nanocrystalline and epitaxial In2O3 thin films was carried out. Transient characteristics of conductivity under step changes of oxidizing conditions caused by surrounding atmosphere changing (air ↔ N2) and (air ↔ O3) have been analyzed and the main regularities were identified. Experiments were performed at operation temperatures from 150 to 400 °C, which correspond to the reproducible conductivity responses to oxidizing and reducing atmospheres. During step changing of the oxidizing properties of surrounding atmosphere, kinetic experiments revealed practically identical transient patterns in both photoconductivity and dark conductivity. An anomalous large magnitude of photocurrent within mm-scale length In2O3 samples was found. Spectral dependencies of photocurrent have revealed some features near photon energy 2.9 eV that is about 0.5 eV smaller than the fundamental optical band gap of In2O3. The appearance of a peak near 2.9 eV under ozone exposure, and subsequent disappearance of this peak under hydrogen exposure were noted. The mechanism of photoconductivity in nanoscale In2O3 films and the role of chemisorbed oxygen in analyzed effects were discussed and semi-quantitative model was proposed.