Growth of high-quality ZnO films on Al2O3 (0001) by plasma-assisted molecular beam epitaxy

High-quality epitaxial ZnO films were grown on alpha-Al2O3 substrates using Cr2O3 buffer layers by plasma-assisted molecular beam epitaxy (PA MBE). The Cr2O3 buffer layer was formed through the oxidation of a thin CrN layer pre-deposited on the (0 0 0 1) Al2O3 substrate, using an O-plasma treatment. From the reflection high-energy electron diffraction (RHEED) and grazing incident X-ray diffraction (GIXRD) analyses, the epitaxial relationship between sequential layers was determined to be [2 (1) over bar (1) over bar 0]ZnO// [1 (1) over bar 0 0]Cr2O3//[0 1 (1) over bar ]CrN//[1 (1) over bar 0 0]Al2O3 and [1 (1) over bar 0 0]ZnO//[1 (2) over bar 1 0]Cr2O3//[1 (2) over bar 1]CrN//[1 (2) over bar 1 0]Al2O3, respectively. The atomic force microscope (AFM) image of ZnO that had grown on the Cr2O3 buffer layer clearly showed steps and terraces on the surface. The Cr2O3 buffer layer was found to be very effective in improving crystal quality, as expressed by the narrowing of the omega-rocking curve full-width at half-maximum of the (0 0 0 2) ZnO diffraction peak (85 arcsec) and the smooth surface morphology (root-mean-square=0.47 nm) of the ZnO films. (c) 2008 Elsevier B.V. All rights reserved.