Hydrogen in the Semiconducting Oxides Tin Oxide and Titanium Oxide Studied by FTIR Spectroscopy.

摘要

In this study, hydrogen-containing defects in two semiconducting metal oxides, SnO2 and TiO2, have been investigated by FTIR spectroscopy. Transparent conducting oxides are unusual but highly useful materials that combine transparency in the visible range with electrical conductivity. With these unique properties, applications utilizing these materials have been continuously growing in several fields, such as display technology, solar cells, and optoelectronics.;Defects or impurities in the crystal structure of transparent conducting oxides affect the properties of these materials. Although hydrogen is the simplest atom, as an impurity, it plays remarkable roles in the electrical and optical properties of metal oxides. For example, recent research has suggested that hydrogen centers are responsible for the n-type conductivity in many metal oxides, in contrast to the traditionally accepted idea that native defects, such as oxygen vacancies and cation interstitials, are the source of conductivity. In order to utilize transparent conducting oxides to their highest potential, the conductivity needs to be controlled and engineered. However, a modern understanding of the conductivity of transparent conducting oxides and the role played by hydrogen is still at an early stage. In this study, IR spectroscopy experiments have been performed to probe the structures and reaction of hydrogen related centers and their relationship to changes in the conductivity of SnO 2 and TiO2.;In SnO2, the relationship between H and the free carriers it introduces has been investigated. The thermal stability of the free carrier absorption and its relationship to the thermal stabilities of the O-H lines have been examined. Distinctive polarization properties of several O-H centers have been used to test microscopic defect models. Temperature dependent interactions between electrically active and inactive defects have been identified by annealing studies.;Studies of TiO2 have focused on the fundamental O-D center and the strong dependence of its vibrational spectrum on temperature. The behavior of three closely spaced O-D lines have been studied by IR spectroscopy and theory and explained with a small polaron model.