Light-induced Charge Transport In LiNbO₃:Fe Crystals

Lithium niobate (LiNbO3, LN) crystal possess the photorefractive effect, but its sensitivity is small. LiNbO3crystal grown with doping iron has excellent photorefractive properties. These excellent properties make it the most promising volume holographic storage photorefractive materials.Study of photorefractive effect mechanism is the important premise of photorefractive materials for practical device. To the study progress on Light-induced charge transport, two kinds of charge transport model have been set up. One is the two-center band transport model, another is the jump model. These two models are able to explain some photorefractive phenomena separately, but the charge migration patterns that they described are quite different. What is the model which close to real photo-induced charge transfer process? To solve this problem, this thesis is to Study of the microscopic process of charge transfer of Fe-doped congruent lithium niobate crystals, by measuring the transient photoconductivity decay characteristics.In this thesis, we study Light-induced charge transport of Fe:LiNbO3using photoconductive instantaneous decay method. We must choose appropriate pulse laser, and measuring instruments frequency based on sample’s absorption character and conductance value range. experiments are performed on samples with different iron concentration in different intensity pulsed light irradiation. Through the analysis of the experimental data. We obtained the dark decay characteristics of photoconductive. Derived from the theory of photoinduced charge transfer process, we establish the photoinduced charge transfer model.The experimental results show that using photoconductive instantaneous decay method can distinguish hop transmission electron and the electrons transmission in the conduction band. From the experimental results, the decay of photo-conductivity can be fitted with a exponential function and a stretched-exponential function. With experimental results, we proposed a charge transfer model which includes the migration of electrons in the conduction band and jumping of electrons between small-polarons. The model better explains the main features of photo-conductivity decay for Fe-doped congruent lithium niobate crystals.