Conducting interfaces between LaAlO3 and thick homoepitaxial SrTiO3 films for transferable templates

Abstract

For the mechanical stability of heterostructure membranes such as LaAlO3 (LAO)/SrTiO3 (STO), which is well-known for two-dimensional electron transport at the interface, a thick template substrate layer is required. However, thick STO films typically suffer from the formation of undesired point defects, mainly due to its cation off-stoichiometry, which results in the insulating interface with LAO. Herein, we report the successful fabrication of a conducting interface between LAO and thick homoepitaxial STO films by pulsed laser deposition. The careful optimization of laser ablation parameters including laser energy density and laser spot size led to stoichiometric 500 nm–thick STO films that have a lattice structure identical to that of bulk single crystals of STO, as confirmed by X-ray diffraction and temperature-dependent Raman spectroscopy. The interface between 4 nm–thick LAO and 500 nm–thick stoichiometric STO films exhibited a metallic behavior at low temperature down to 4 K, implying a low concentration of point defects in the homoepitaxial STO film. Ultimately, a crack-free, millimeter-sized 500 nm–thick STO membrane was successfully fabricated. These results are expected to facilitate the integration of high-quality complex oxide heterostructure membranes with various substrates including silicon, enabling their practical applications.