The role of hydrogen and oxygen in the persistent photoconductivity of strontium titanate

Annealed strontium titanate (SrTiO3 or STO) single crystals exhibit persistent photoconductivity (PPC) at room temperature. Illumination with sub-gap light reduces the resistance by three orders of magnitude, which persists for weeks or longer. The defects responsible for this remarkable phenomenon have not been identified. In this work, we report on the importance of hydrogen and oxygen during the annealing process that is used to induce PPC. The results from IR spectroscopy and two-point resistance measurements indicate that water vapor at 1200 degrees C yields hydrogen and oxygen-vacancy populations that result in large PPC. Deuterium substitution experiments show evidence for a two-hydrogen center that forms after exposure to light. The results suggest that light causes substitutional hydrogen to leave the oxygen site, forming metastable O-H bonds. This process liberates electrons and causes PPC. Published by AIP Publishing.