Epitaxial Ba_0.5Sr_0.5TiO₃-GaN heterostructures with abrupt interfaces

Epitaxial heterostructures incorporating the complex ferroelectric oxide Ba_0.5Sr_0.5TiO₃ (BST) and GaN were prepared using a combination of RF magnetron sputtering and metalorganic chemical vapor deposition for the respective layers. The heterostructures were grown on c-plane sapphire substrates and were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM). This analysis showed that at substrate temperatures of 650 °C, BST films grow epitaxially on GaN with a {1 1 1} orientation and that the GaN-BST interface is smooth and abrupt, with disorder confined to grain boundaries and the interface plane. The film morphology is grainy indicating a 3-D growth mode. High-temperature post-deposition annealing studies suggest no interface reactions up to 900 °C. These results demonstrate that complex oxides like BST can be integrated with wide bandgap semiconductors like GaN and open exciting possibilities for new multifunctional devices.