Persistent Photoconductivity (PPC) in oxygen-ion implanted KNbO3( oriented bulk single crystals; perovskite structure; ferroelectric with a band gap of 3.16 eV) is studied in air at room temperature to prevent the degradation of its crystallinity caused by the phase transition. The residual hydrogens in un-implanted samples are estimated to be 5×1014 cm−2from elastic recoil detection analysis (ERDA). A multiple-energy implantation of oxygen ions into KNbO3is performed using energies of 200, 400, and 600 keV (each ion fluence:1.0×1014 cm−2). The sheet resistance varies from >108 Ω/□ for an un-implanted sample to 1.9×107 Ω/□ for as-implanted one, suggesting the formation of donors due to hydrogen interstitials and oxygen vacancies introduced by the ion implantation. The PPC is clearly observed with ultraviolet and blue LEDs illumination rather than green, red, and infrared, suggesting the release of electrons from the metastable conductive state below the conduction band relating to the charge states of the oxygen vacancy.
Tsuruoka, R., Shinkawa, A., Nishimura, T., Tanuma, C., Kuriyama, K., & Kushida, K. (2016). Persistent photoconductivity in oxygen-ion implanted KNbO3bulk single crystal. Solid State Communications, 248, 120–122. https://doi.org/10.1016/j.ssc.2016.09.020