Epitaxial growth of Zn-rich (Mg,Zn)O thin films on MgO substrates with different surface orientations

(Mg,Zn)O films with various growth orientations were prepared on the MgO substrates with different surface structures using oxygen plasma-assisted molecular beam epitaxy. X-ray diffraction (XRD) revealed that the crystallographic orientation of (Mg,Zn)O thin films transforms from the polar c-plane (0001) to a two-fold-symmetry inclined plane and then to the nonpolar m-plane (10-10) as the substrate template changes from MgO(111) to MgO(011) and then to MgO(001). In addition, the surface topography and film roughness were monitored by atomic force microscopy. Interestingly, the electronic structures of the three films exhibited orientation-dependent features, as revealed by synchrotron-based X-ray absorption spectroscopy. In addition, all of the (Mg,Zn)O thin films showed high optical transmittance (over 85%, 400-800 nm) and large energy gaps (around 3.33 eV). Our systematic study of the substrate-influenced film characteristics demonstrates a method of tailoring thin films using the same substrate with different crystallographic orientations.