X-ray reflectivity characterization of ZnO/Al2O3 multilayers prepared by atomic layer deposition

Specular X-ray reflectivity (XRR) has been employed in the characterization of a novel series of ZnO/Al2O3 multilayer materials prepared by atomic layer deposition in a custom-built hot-wall reactor. All multilayers studied are approximately 1200 Angstrom thick and consist of 1-128 ZnO/Al2O3 bilayer subunits. Reflectivity data are treated both qualitatively and quantitatively by computer-aided simulation and modeling. Surface roughness is observed to increase dramatically with increasing ZnO layer thickness. ZnO density is determined to be within 5% of bulk values, while the Al2O3 layers exhibit densities less than 80% of that expected for crystalline alumina. Thickness parameters determined by computer simulation correspond to deposition rates of 1.71 and 1.28 Angstrom/reaction cycle for ZnO and Al2O3, respectively. XRR-determined thickness and density parameters are in clear quantitative agreement with analyses of single-component films by other techniques. Conventional and grazing-incidence X-ray diffraction show the ZnO layers to be polycrystalline above a critical layer thickness of approximately 10 Angstrom. The Al2O3 layers are amorphous.