Effects of Grain Boundaries in Metal-insulator Transition of SrTiO3 under UV/Visible Light Irradiations

Transitions from insulator to conductor can be observed in both SrTiO 3 single crystal and polycrystalline, but their detectivities are clearly different. Under UV irradiation (405 nm, 3.06 eV), the detectivity for the single crystal (8.01 x 1011 Jones) is significantly higher than that detected in the polycrystalline (8.94 x 1010 Jones). Interestingly, under irradiation with green laser (532nm, 2.33 eV), higher detectivity in the polycrystalline (4.41 x 1010 Jones) than the single crystal (1.46 x 1010 Jones) is observed, indicating that the enhanced photocurrent or detectivity are governed by the larger amount oxygen vacancies contributed from the grain boundary in the polycrystalline.