Spectroscopic investigation of photovoltaic effect and photoconductivity in undoped and Mg-doped near-stoichiometric LiTaO3 crystals

We investigated the saturation space-charge field by directly measuring photovoltaic current and photoconductivity in series of undoped (61 mol% Li2O in the melt) and Mg-doped (0.5, 1, 1.2,1.4 mol%) near-stoichiometric LiTaO3 crystals, where the two z-planes of crystals were coated with Au and a DC field was applied along the z- axis of the samples in a vacuum chamber. The wavelength (UV/visible) dependence of photovoltaic coefficient, specific photoconductivity, and saturation space-charge field were presented. The saturation space-charge field decreases with increasing the concentration of MgO and decreasing wavelength. The minimum space-charge field is only 40 V/m with the wavelength of 350 nm in the 1.4 mol % Mg-doped LiTaO3 because of huge increase of photoconductivity.