Hydrogen is the prime suspect for persistent photoconductivity in SrTiO₃

When annealed at 1200°C, strontium titanate (SrTiO₃) exhibits large persistent photoconductivity (PPC) at room temperature. Upon exposure to sub-band-gap light, the resistance drops by 3 orders of magnitude, a change that persists “forever” after the light is turned off. Recently PPC was exploited to write a conductive path on a crystal, using a 405 nm laser. The defect responsible for this remarkable effect has not been identified. In this talk, the results of varying the annealing gas will be discussed. The experiments provide evidence that light causes hydrogen to leave the substitutional oxygen site and form O-H bonds. This liberates electrons, causing PPC.