Stoichiometry and Termination Control of LaAlO₃/SrTiO₃ Bilayer Interfaces

Driven by the interest in fundamental physics and potential applications in novel electronic devices, intense effort is devoted to integration of oxide-based 2D electron gases (2DEGs) with other functional materials. As a classic model system, LaAlO₃/SrTiO₃ (LAO/STO) has gained significant attentions. However, due to limitations in synthesis and high demands on the involved thin films, the formation of conductive interfaces between artificially grown STO and LAO thin films is an extreme challenge; oftentimes these interfaces remain insulating or show poor transport properties, which inhibits the development of all-thin-film devices. Here, by adopting high temperature growth to achieve step-flow growth mode and fine-tuning the laser fluence during pulsed laser deposition, high quality homoepitaxial STO thin films with sufficiently low point-defect concentration and controllable surface termination are obtained. Fully metallic 2DEGs are then realized at interfaces between STO thin films and both crystalline and amorphous LAO overlayers. The observed slightly reduced mobility in the bilayer LAO/STO/STO structures as compared with single-layer LAO/STO structures is related to residual defect formation during STO synthesis, yielding a disordered metallic oxide system. The results give prospect of multilayer interfaces potentially accessible in superlattice structures and provide a reliable starting point for back-gated all-thin-film field-effect devices.