Polarity dependence and characterization of high-quality homoepitaxial ZnO layers grown on {0001} ZnO substrates

Abstract

We present our first results for the growth of ZnO layers by Molecular Beam Epitaxy on commercial {0001} ZnO substrates of different polarities. On O-face oriented substrates, a two-dimensional growth mode was achieved as verified by the presence of a streaky Reflection High-Energy Electron Diffraction (RHEED) pattern and a faint (3x3) reconstructed surface. Moreover, a distinct specular spot and reproducible RHEED oscillations were found. On the other hand, the RHEED pattern for the growth on Zn face ZnO substrates was spotty indicating three-dimensional growth, and a lateral coherence length of the layer of only 88 nm was estimated by Williamson-Hall plots. Bound exciton lines in low temperature photoluminescence for a layer on an O-face ZnO substrate were narrow (FWHM: 1.8 meV) compared to the substrate material, while the root mean square roughness measured by Atomic Force Microscopy was 20 nm.