Large-Area Growth of Perovskites on γ-Al₂O₃: A Route to Oxide Electronic Materials

Perovskite oxides offer diverse compositions, structures, and properties that can be carefully controlled through epitaxial synthesis methods, presenting vast opportunities in electronic or optoelectronic applications. SrTiO₃ exhibits a fascinating range of electronic phenomena, including quantum electronic transport and superconductivity. Doping SrTiO₃ via Nb substitution holds promise in thermoelectrics and as electrodes for ferroelectric or multiferroic oxides. A key challenge has been in achieving epitaxial synthesis of SrTiO₃ over large areas. Synthesis methods have been constrained by the substrate dimensions traditionally employed for perovskite epitaxy. We have employed solid phase epitaxy to synthesize low-defect-density γ-Al₂O₃ on commercial α-Al₂O₃ substrates, available in large dimensions, underpinning the feasibility of large-area epitaxial synthesis. The (111) surface of cubic γ-Al₂O₃ has a lattice constant twice that of typical pseudocubic perovskites and thus provides an appropriate template for growth of perovskites. Epitaxial growth of Nb-doped SrTiO₃ on γ-Al₂O₃ yields thin films with improved structural and electronic properties compared to those grown on α-Al₂O₃, including electronic conductivity that is two to three orders of magnitude higher. The epitaxial formation of SrTiO₃ (111) on γ-Al₂O₃ (111) heralds a noteworthy instance of nonisomorph epitaxial growth between a perovskite and a spinel, bridging the two predominant oxide material classes.