OBSERVATION AND INTERPRETATION OF PHOTOCURRENTS IN KTAO3-LI SINGLE-CRYSTALS

Photoconductivity has been observed at T < 80 K in disordered ferroelectric K1-xLixTaO3 (KTL) with 0.016 less than or equal to x less than or equal to 0.05. Under argon laser illumination with energy lower than the KTL band gap width, the photocurrent value in KTL was of the same order as in conventional semiconductors with impurities. The dependence of the photoconductivity on temperature, Li concentration, external electric field, illumination power and history of sample was studied. Using a model which takes into account the displacement of the oxygen atoms next to the off-center position of Li+, an energetic scheme of the local levels in the band gap, which includes shallow oxygen local level and those of involuntary iron ions, is proposed.