Epitaxial growth of non-polar a-plane AlN films by low temperature sputtering using ZnO buffer layers

This article presents an investigation on the epitaxial growth of non-polar a-plane AlN thin films by low temperature sputtering using ZnO buffer layers. Prior to the deposition of the AlN films, epitaxial growth of a-plane ZnO thin films on r-plane sapphire substrates was performed by a metalorganic chemical vapor deposition (MOCVD). The effect of MOCVD growth conditions on surface morphology and crystallinity of ZnO epi-layer was examined to optimize the growth process of buffer layer. The resulting ZnO epi-layers were used as buffer layers to grow non-polar AlN by low temperature sputtering. The measurements of XRD 2theta/omega- and phi-scans indicate that the epitaxial relationship among AlN, ZnO and sapphire substrate is 112¯0AlN//112¯0ZnO//11¯02Al2O3 and 11¯00AlN//11¯00ZnO//112¯0Al2O3. Cross-sectional transmission electron microscopy (XTEM) revealed that no reactive intermediate layers formed at the interfacial region between AlN film and ZnO buffer layer. The a-plane ZnO layers can be used as lattice matched templates for epitaxial growth of non-polar AlN by low temperature sputtering.