Effects of an extremely thin buffer on heteroepitaxy with large lattice mismatch

We report on an experimental study of buffer mechanism in plasma-assisted molecular-beam epitaxy of ZnO on ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{(0001)}$ with a MgO buffer. It lowers the surface energy and provides nucleation cores. As a result, lateral epitaxial growth of ZnO becomes favorable from the initial growth stage. The MgO buffer also affects the generation of dislocations in such a way that it reduces their density by introducing dislocation interactions. This study suggests that by employing an appropriate buffer to modify the initial nucleation environment, high quality heteroepitaxy is achievable even with large mismatch.