Deep level transient spectroscopy was carried out to investigate the origin of the deep levels in the band gap of anatase Ti O2. The epitaxial anatase- Ti O2 film grown by metal-organic chemical vapor deposition possessed a deep level whose activation energy was 0.52 eV. In contrast, this deep level at 0.5 eV was not observed in the films grown by sputtering. However, by adding C H4 or H2 to the sputtering gas, the deep level at 0.5 eV was observed in the sputter-grown films. Furthermore, the density of this deep level increased with increasing hydrogen gas, suggesting that this deep level originated from hydrogen doping.
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