Non-steady-state photoelectromotive force in bipolar photoconductors with arbitrary level structure

Abstract

Space-charge grating formation and the non-steady-state photoelectromotive force (photoEMF) excited by a vibrating interference pattern are analyzed for the general case of a photorefractive semiconductor with bipolar dark conductivity and photoconductivity. The calculation is performed in the linear approximation of interference pattern contrast with the use of average carrier generation rates, contrasts, and diffusion lengths as phenomenological parameters without any detailed specification of the crystal impurity-level structure. This approach permits classification of possible types of space-charge and photoEMF dependence for bipolar photoconductors and predicts some new phenomena, in particular the disappearance of the resonance maximum in the frequency response and the inversion of sign of the photoEMF signal observed under a high external dc electric field in the case of different contrasts of the carrier generation rates.