Hopping model of photogalvanic effect in ferroelectrics

A hopping mechanism of photogalvanic effect (PGE) in ferroelectrics is proposed. PGE arises due to asymmetry of inter-center photoexcitation and recombination of localized electrons. Calculation of the effect is carried out in a model of dipole impurities. The dipole moment of the impurity mixes states of opposite parity of localized electron. This mixing leads to asymmetry of electron wave functions. Therefore matrix elements describing photoexcitation to the excited state of nearest neighbour are different for the left and right neighbours. Magnitude of the matrix elements is determined by exponential tails of the wave functions. The cases of high and low compensation are considered. Estimations of the PGE current and the Glass constant are carried out and it is shown that they are in agreement with experimental values. In case of an isolated crystal static electric field arises. Its value can be very large (E ∼ 104-105 v/cm) because of low mobility of photoelectrons.