Non-steady-state photoelectromotive force in semiconductor photorefractive crystals biased by dc field

Abstract

A microscopic model of the non-steady-state photoelectromotive force excited by a vibrating interference pattern in a bipolar photoconductor under an external dc electric field is elaborated for the case in which the lifetime of one type of carrier is longer than the dielectric relaxation time. It is shown theoretically that when two types of carriers with different relaxation times are used their presence leads to some new effects in non-steady-state photoelectromotive-force behavior. First, the frequency transfer function presents a two-shelf form (i.e., it has two regions in which the signal is frequency independent) instead of the high-pass band filter form usually seen with the monopolar model. Second, for both frequency shelves under an external dc field one can observe anomalous quadratic growth of the photoelectromotive-force signal amplitude without change of its sign. Unusual spatial-frequency dependencies typical for this model are also discussed. The analysis is used to explain effects observed in GaAs in the visible and the near-IR spectral regions for which interband optical absorption is typical, with both types of carriers being efficiently generated.