Epitaxial growth of (100)-oriented ceria film on c-plane GaN/Al2O3 using YSZ/TiO2 buffer layers by pulse laser molecular beam epitaxy

Ceria (CeO2) films with fluorite structures were grown on c-axial-oriented GaN/Al2O3 substrates with and without YSZ/TiO2 double-bridge layer using pulse laser molecular beam epitaxy, respectively. The growth behavior was in situ monitored by reflection high-energy electron diffraction (RHEED). The epitaxial orientation relationship was confirmed by the x-ray diffraction (XRD) technique. With the introduction of the YSZ/TiO2 double-buffer layer, high-quality a-axial-oriented CeO2 films were successfully grown on GaN substrate. The epitaxial relationships of this heterostructure were CeO2(200)parallel to YSZ(200)parallel to TiO2(200)parallel to GaN(0002) and CeO2[010]parallel to YSZ[010]//TiO2[001]//GaN[11 (2) over bar0]. XRD and RHEED analyses reveal in-plane tensile strain in CeO2 film, which is mainly caused by lattice mismatch. The in-plane alignment of CeO2 film on YSZ/TiO2 bridge layer is attributed to the interface stress between the film and substrate. Furthermore, without the YSZ/TiO2 buffer layer, CeO2 film directly grown on GaN was oriented along the [111] direction. The different out-of-plane orientations of CeO2 films on GaN substrate could be explained by the different in-plane crystallographic symmetries of templates. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3574523]