Growth of hexagonal gallium nitride films on the (111) surfaces of silicon with zinc oxide buffer layers

Abstract

The growth of gallium nitride films on sapphire substrates has not been straightforward because of the large lattice mismatch between gallium nitride and sapphire. Zinc oxide is structurally the closest material to gallium nitride and therefore is finding use as the substrate for gallium nitride. Single crystal wafers of zinc oxide are hard to obtain and very expensive. However, a thin layer of zinc oxide on a suitable substrate might solve this problem. In this work, highly c-axis oriented zinc oxide buffer layers were grown on Si(111) substrates at temperatures 410-540°C by chemical vapor deposition of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)zinc, Zn(tmhd)2, and the hexagonal GaN films were subsequently deposited on them at 500 °C using the single precursor tris(diethyl-μ-amido-gallium), [(C2H5)2GaNH2]3. The compound Zn(tmhd)2 was found to require oxygen for the deposition of zinc oxide. In the case of gallium nitride, low pressure chemical vapor deposition of tris(diethyl-μ-amido-gallium) worked reasonably well with or without a carrier gas. The buffer layers and the GaN films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and reflection high energy electron diffraction (RHEED).