Abstract
New single cyrstals of Gd 2 O 3 and Y 2 O 3 were found to grow epitaxially on GaN in ultra-high vacuum. In-situ reflection high-energy electron diffraction reveals a six-fold symmetry in the in-plane epitaxy of the rare earth oxides. Single-crystal x-ray diffraction measurements find that these single-crystal oxide films are indeed the high temperature hexagonal phases of the sesquioxides, stabilized by the GaN substrate epitaxy. Despite a large mismatch in lattice constant, the fully relaxed oxide films are of excellent structural quality.