Growth of high-quality ZnO films on Al 2O 3 (0 0 0 1) by plasma-assisted molecular beam epitaxy

Abstract

High-quality epitaxial ZnO films were grown on α-Al 2O 3 substrates using Cr 2O 3 buffer layers by plasma-assisted molecular beam epitaxy (PA MBE). The Cr 2O 3 buffer layer was formed through the oxidation of a thin CrN layer pre-deposited on the (0 0 0 1) Al 2O 3 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¯ 1¯0]ZnO//[1 1¯ 0 0]Cr 2O 3//[0 1 1¯]CrN//[1 1¯ 0 0]Al 2O 3 and [1 1¯ 0 0]ZnO//[1 2¯ 1 0]Cr 2O 3//[1 2¯ 1]CrN//[1 2¯ 1 0]Al 2O 3, respectively. The atomic force microscope (AFM) image of ZnO that had grown on the Cr 2O 3 buffer layer clearly showed steps and terraces on the surface. The Cr 2O 3 buffer layer was found to be very effective in improving crystal quality, as expressed by the narrowing of the ω-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.