Persistent Photoconductivity in Strontium Titanate

Persistent photoconductivity was observed in strontium titanate (SrTiO3) single crystals. When exposed to sub-bandgap light (2.9 eV or higher) at room temperature, the free-electron concentration increases by over 2 orders of magnitude. After the light is turned off, the enhanced conductivity persists for several days, with negligible decay. From positron lifetime measurements, the persistent photoconductivity is attributed to the excitation of an electron from a titanium vacancy defect into the conduction band, with a very low recapture rate.