Structure and ferroelectric photovoltaic effect modulation in the epitaxial BiFeO3/La0.5Sr0.5CO3 heterostructures

Square-shaped BiFeO₃ (BFO) thin films were prepared on SrTiO₃ (STO) substrates by off-axis magnetron sputtering using La_0.5Sr_0.5CoO₃ (LSCO) as the bottom electrode, and both LSCO and BFO are perovskite structure. The BFO crystalline quality improves and the grain size becomes larger as the thickness H increases, and both have smaller mean square roughness. The effects of BFO thickness H, light intensity I_p and ambient temperature AT on the ferroelectric photovoltaic effect (FPE) for the Pt/BFO/LSCO heterostructures are significant. With the H increase, the open-circuit voltage V_oc and short-circuit current J_sc increase linearly, with V_oc up to 0.44 V. The short-circuit current modulation intensity ΔJ_sc follows the ΔJ_sc-300>ΔJ_sc-200>ΔJ_sc-100 rule. With the I_p increase, Pt/BFO(300 nm)/LSCO’ J_sc increases linearly, and V_oc first increases and then tends to saturation, which satisfies Glass' law. With the AT increases, V_oc is linearly decreasing and J_sc shows the law: decreasing→increasing→decreasing. The polarization-modulated FPE mechanism is investigated by analyzing the Pt/BFO/LSCO energy band structure, which is attributed to the coupling effect between the BFO depolarization field (E_dp) and the built-in electric field at the interface (E_Pt/BFO & E_BFO/LSCO), and the FPE mechanism is shifted from the interface barrier domination to the ferroelectric polarization domination as H increases.