Origin of Negative Photoconductivity at the Interface of Ba_0.8Sr_0.2TiO₃/LaMnO₃/Ba_0.8Sr_0.2TiO₃ Heterostructures

The study of Ba_0.8Sr_0.2TiO₃/LaMnO₃/Ba_0.8Sr_0.2TiO₃ heterostructures on a MgO substrate with Ba_0.8Sr_0.2TiO₃ ferroelectric films revealed the occurrence of a metallic character of the temperature behavior of the resistance at a temperature less than 175 K. This behavior is associated with an increased charge concentration at the interface due to a discontinuity in the ferroelectric polarization at the interface between the films. At these temperatures, the effect of negative photoconductivity is observed under uniform illumination with the light of a selected spectral composition event on the surface of the ferroelectric film. The combined exposure to green and infrared light led to an addition of the effects. As a result, a cumulative effect was observed. The effect of metallic conductivity is due to the discontinuity of ferroelectric polarization. Therefore, we explain that the partial screening of the ferroelectric polarization by photogenerated charge carriers causes a reduction in the carrier concentration at the interface. Measurements in the Kelvin mode of atomic force microscopy showed that illumination influences the surface charge concentration in a similar way; this observation confirms our hypothesis.