Epitaxial properties of Co-doped ZnO thin films grown by plasma assisted molecular beam epitaxy

High quality Co-doped ZnO thin Elms are grown on single crystalline Al2O3(0001) and ZnO(0001) substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450, C. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction (RHEED) and ex-situ high resolution x-ray diffraction (HRXRD). The epitaxial thin Elms are single crystal at Elm thickness smaller than 500nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as CO2+ substituting Zn2+ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin Elms are ferromagnetic with Curie temperatures T-C above room temperature.