Hole-electron competition investigated by holographic recording in Bi12TiO20 crystal under applied electric field

Abstract

Hole-electron competition was induced in an undoped Bi12TiO20 crystal using coherent pre-illumination at 532 nm. Photorefractive recording and erasure at 639.7 nm under the action of external electric field E0 were used to theoretically and experimentally investigate the competition within the sample band-gap. The good agreement between theory and experimental data allowed to obtain, in both regimes without and with pre-illumination, the saturation space-charge fields Eq and holes and electrons effective donors concentrations (ND)eff's. The phase shift between the electronic gratings and the hole grating was also computed and revealed a competition behavior between the applied electric field effect of increasing the characteristic lengths of electrons and holes moving in opposite directions in the conduction and valence bands, respectively, and the intensity of decreasing such lengths. The computed holes donor density indicated a strong contribution of the coherent pre-illumination to the hole-electron competition mechanism.