Giant enhancement of the non-steady-state photo currents in photoconductive crystals

We report the nonresonant excitation of the non-steady-state photocurrents in an external sinusoidal electric field. We demonstrate that the application of an AC field sufficiently increases the photocurrent amplitude. At the same time the frequency transfer function of the effect maintains the form typical for the diffusion mechanism of photocurrent excitation. The dependencies of the current amplitude and characteristic cut-off frequency versus applied voltage are utilized for the determination of the photocarrier's μτ-product. The advantages of the proposed technique are discussed. The experiments are carried out in the photorefractive n-type Bi12SiO20 crystal. The signal enhancement of 50 dB has been achieved and μτ-product is found to be μτ = (0.8 - 1.2) 10-10 m2/V.