Activation of Photoelectrochemical Reaction for High Temperature Oxidation Film by Non-stoichiometry Control

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The effect of non-stoichiometry control of oxide on photoelectrochemical characteristics of oxide films formed by high temperature oxidation of metals was investigated. The non-stoichiometry of the oxide films was controlled by a hydrogen reduction treatment and a control of oxygen pressure for preparation of oxide films by the high temperature oxidation of metals. For rutile-TiO_2 film (n-type conduction) formed by the high temperature oxidation of titanium, oxide ion vacancies in the oxide film were introduced by the hydrogen reduction treatment and a lowering of oxygen pressure for the preparation of the films. Photo-anodic current was increased with an increase in the reduction temperature and with the lowering of oxygen pressure for the preparation of film. This suggests that the photo-anodic reaction is activated by the introduction of oxide ion vacancies into the oxide film. For beta-Ta_2O_5 film (n-type conduction) formed by high temperature oxidation of tantalum, the photoanodic current increased with increasing temperature for the hydrogen reduction. It was found from these results that the photo-anodic reaction for oxide semiconductor having n-type conduction was activated by the introduction of oxide ion vacancies into the oxide. For Cu_2O film (p-type conduction) formed by high temperature oxidation of copper, photo-cathodic reaction was activated by a hydrogen reduction at low temperature, by which oxide ion vacancies were induced.Consequently, it has become apparent that the introduction of oxide ion vacancy into oxide film activated the photoelectrochemical reaction for oxide semiconductor electrode without depending on the conduction type.