Photo-conductivity decay properties of Fe-doped congruent lithium niobate crystals

Photo-conductivity transient processes of Fe:LiNbO3 congruent crystals are investigated by electro-chemical analyzer. The experiments are executed with Fe:LiNbO3 crystals of different Fe concentrations in the conditions of different laser intensities. The results show that the transient photo-conductivity of the Fe-doped lithium niobate crystal is formed through a complex process of electron transport; the decay of photo-conductivity can be fitted to an exponential function and a stretched-exponential function. The dependences of the fitting parameters on laser intensity and iron-doped concentration are measured. The values of amplitudes σ1max, σ2max, time constant τ2 and stretching factor β increase strongly at low intensities, and τ2 and β reach their saturation value for higher intensities; with the increase of the concentration of Fe ions, the values of σ1max, σ2max and τ2 incerease, but β decreases. With experimental results, we propose a charge transfer model which includes the migration of electrons in the conduction band and the jumping of electrons between small-polarons. The model better explains the main features of photo-conductivity decay for Fe-doped congruent lithium niobate crystals.