Room Temperature Persistent Photoconductivity of KTaO3

Persistent photoconductivity is a phenomenon in which the conductivity of a material increases upon light exposure and remains without the source of exciting illumination. Potassium tantalate, KTaO₃ (KTO), a cubic perovskite semiconductor with a wide bandgap of 3.6 eV has attracted interest due to its potential applications in electronic and storage devices. In this work, KTO crystals were annealed in a hydrogen-rich, oxygen-poor environment created by sealing them in a silica ampoule with hydrogen gas and tantalum wire, which introduced oxygen vacancies. IR spectroscopy showed a transmission threshold at 340 nm, free carrier absorption, and a reduction of the hydrogen peaks post anneal treatment. Upon exposure to a 340 nm light-emitting diode (LED), the crystals exhibited PPC, as indicated by Hall effect measurements, which showed an increase in n-type conductivity by three orders of magnitude lasting for several weeks. The PPC effect can be reversed via open-air anneal and re-induced by repeating the irradiation.

UV-Vis-NIR spectroscopy demonstrated that different onset energies between free carrier absorption and photochromism suggest distinct defects responsible for each phenomenon.

Positron annihilation spectroscopy revealed an increase in the defect open volume after illumination, offering new insights into the PPC mechanism.