Contrasting the experimental properties of hydrogen in SnO2, In2O3, and TiO2

IR spectroscopy has been used to investigate the properties of H and D in single crystals of the transparent conducting oxides, SnO2, and In2O3. H introduces several O-H stretching lines and also the broad absorption arising from free carriers. IR spectroscopy has been used to identify the sources of n-type conductivity, its thermal stability, and the reactions of H-containing defects. The properties of OH and OD centers in TiO2, while studied for decades, reveal new surprises and properties that are in sharp contrast to the shallow, H-related donors seen in SnO2 and In2O3. Recent theory and EPR experiments find that electrons in TiO2 become self-trapped at Ti sites to form small polarons. The OD center in TiO2 shows a multiline vibrational spectrum with an unusual temperature dependence that can be explained by a small polaron model with the donor electron self-trapped at different Ti sites near the OD oscillator. (C) 2014 AIP Publishing LLC.