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. Using interlayer interaction through the internal charge transfer to control functional heterostructures with atomic-scale design has become one of the most effective interface-engineering strategies nowadays. Here, we demonstrate the effect of a crystalline LaFeO3 buffer layer on amorphous and crystalline LaAlO3/SrTiO3 heterostructures with 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. For the amorphous and crystalline LaAlO3/SrTiO3 heterostructures, the corresponding metal-to-insulator transition is found when the LaFeO3 buffer layer thickness crosses 3 and 6 unit cells, respectively. 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.