Extrinsic and intrinsic charge transfer at interfaces of membrane-based oxide heterostructures

Engineering complex oxide heterostructure and their interfaces revealed plethora of emergent electronic and magnetic properties. The advances in free-standing oxides and subsequent integration with semiconductors has further revolutionized the scope of building modern electronic architecture. However, delaminating atomically defined epitaxial oxide film and controlling their unique defect structure and charge transfer mechanism at interface on such architectures remains an open challenge. Here, we report a comprehensive study by growth control of the surface termination of SrTiO₃(STO) thin films and subsequent transfer of TiO₂ terminated STO lamella on Silicon (Si) via sacrificial layer route. This approach yields atomically smooth, step-terraced membrane-based substrates on silicon support. These serve as an ideal template for the growth of LaAlO₃/SrTiO₃ heterostructures, to study the charge transfer mechanism. We probe the interfacial charge trasnsfer mechanism via X-ray photoelctron spectroscopy (XPS). We show that Ti⁴⁺ /Ti³⁺ state reveals distinct signature of growth induced oxygen vacancy and intrinsic electronic charge transfer. Specifically, we trigger a cross-over from redox-driven extrinsic charge transfer to intrinsic electronic charge transfer by systematic variation of growth and annealing conditions. To disentangle extrinsic doping via growth-induced oxygen vacancy formation from intrinsic doping via intrinsic electronic charge transfer we study the thermodynamic redox response of the heterostructure. We employ in-situ x-ray photoemission spectroscopy and thereby correlate the interplay of confinement-phenomena, redox-chemistry & growth kinetics. These results show that controlling intrinsic and extrinsic charge transfer may allow to tailor and fine tune charge carriers and their confinement in freestanding oxide heterointerfaces, making them suitable for oxide electronics on Si and designing heterostructure beyond conventional epitaxy.