Characteristic Lengths of Interlayer Charge-Transfer in Correlated Oxide Heterostructures

Electronic devices in the form of high mobility conducting channel with charge carriers can be regulated through the internal charge transfer or chemical doping. Here, we demonstrate the effect of a crystalline LaFeO₃ buffer layer on amorphous and crystalline LaAlO₃/SrTiO₃ heterostructures with a different characteristic length of interlayer charge transfer. The LaFeO₃ buffer layer acts as an energetically favored electron acceptor in both LaAlO₃/SrTiO₃ systems, resulting in modulation of interfacial carrier density and hence metal-to-insulator transition. Such different critical LaFeO₃ thicknesses are explained in terms of distinct characteristic lengths of the redox-reaction-mediated and polar-catastrophe-dominated charge transfer, controlled by the interfacial atomic contact and Thomas-Fermi screening effect, respectively. Our results not only shed light on the complex interlayer charge transfer across oxide heterostructures but also establish a new route to precisely tailor the charge-transfer process at a functional interface by atomically engineered buffer layers.