A reversible positive and negative photoconductivity behavior modulated by polarization effect

Negative photoconductive devices exhibit a significant reduction in conductivity under illumination, enabling high-contrast optical modulation and promising great potential in optics. In this study, an ITO/BFCO/TiO2/FTO device was simply fabricated through a synergistic application of sol-gel and magnetron sputtering techniques. Interestingly, the ferroelectric polarization can be reversibly modulated by a low bias voltage in the ITO/BFCO/TiO2/FTO device, thereby exhibiting bipolar voltage dependent reversible behavior of positive and negative photoconductivity. This mechanism has been discussed, where the combined effect of illumination and applied voltage induces internal polarization reversal in Bi2FeCrO6, leading to a transition in the resistance state from low to high. This transition results in an elevation of the energy band, thereby impeding the migration of charge carriers. Additionally, femtosecond laser transient absorption spectroscopy reveals redshift in the initial absorption peak, indicating changes in the band structure induced by illumination, crucial for understanding carrier dynamics in a non-equilibrium state.