Layer-by-layer growth of ZnO epilayer on Al2O3(0001) by using a MgO buffer layer

By introducing a thin MgO buffer, layer-by-layer growth of ZnO epilayers on Al2O3(0001) substrates is achieved by plasma-assisted molecular beam epitaxy. The MgO buffer is very effective on the improvement of surface morphology during the initial growth stage, which eventually leads to an atomically flat surface. As a result, (3x3) surface reconstruction of ZnO is observed and reflection high-energy electron diffraction intensity oscillations are recorded. Structural analysis indicates that the twin defect with a 30 degrees in-plane crystal orientation misaligned is completely eliminated, while the total dislocation density is reduced. Free exciton emissions at 3.3774 eV (X-A) and 3.383 eV (X-B) are observed in photoluminescence at 4.2 K further indicating the high quality of the resulting ZnO epilayers. (C) 2000 American Institute of Physics. [S0003-6951(00)02405-0].