Epitaxial Ba0.5Sr0.5TiO3-GaN heterostructures with abrupt interfaces

Epitaxial heterostructures incorporating the complex ferroelectric oxide Ba0.5Sr0.5TiO3 (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 degrees C, BST films grow epitaxially on GaN with a {111} 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 degrees 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. (C) 2008 Elsevier B.V. All rights reserved.