MOCVD of ZnO thin films for potential use as compliant layers for GaN on Si

This paper explores the use of nanostructured zinc oxide (ZnO) films as a compliant buffer layer for the growth of gallium nitride (GaN) on silicon substrates. Thin films of ZnO have been deposited on silicon (111) substrates by liquid injection metalorganic chemical vapour deposition (MOCVD) using dimethyl zinc-tetrahydrofuran adduct and oxygen. The use of the adduct complex avoids prereaction between the dialkyl zinc complex and oxygen which has been observed elsewhere. ZnO films deposited by this method were stoichiometric and of high purity, with no detectable carbon contamination. Films were deposited over a temperature range 350-550 degrees C, and exhibited a nanowire-like morphology. Subsequent deposition of GaN layers grown by molecular beam epitaxy (MBE) on the ZnO film resulted in the transformation of the nanowires to gallium oxide, accompanied by virtually complete removal of zinc from the layer. A heteroepitaxially oriented (c-axis) GaN/gallium oxide/silicon structure was produced after the nitride deposition which consisted of characteristic columnar GaN with the GaN[0001]parallel to Si [111]. Selective area electron diffraction of the by-product oxide interlayer showed a polycrystalline-like behaviour that gave rise to a random azimuthal distribution of the GaN grains. (C) 2007 Elsevier B.V. All rights reserved.