Epitaxial growth of Sb-doped nonpolar a-plane ZnO thin films on r-plane sapphire substrates by RF magnetron sputtering

Abstract

► Sb-doped nonpolar a -plane ZnO layers were epitaxially grown on sapphire substrates. ► Crystallinity and electrical properties were studied upon growth condition and doping concentration. ► The out-of-plane lattice spacing of ZnO films reduces monotonically with increasing Sb doping level. ► The p-type conductivity of ZnO:Sb film is closely correlated with annealing condition and Sb doping level. In this study, the epitaxial growth of Sb-doped nonpolar a -plane ( 1 1 2 ¯ 0 ) ZnO thin films on r -plane ( 1 1 ¯ 0 2 ) sapphire substrates was performed by radio-frequency magnetron sputtering. The influence of the sputter deposition conditions and Sb doping concentration on the microstructural and electrical properties of Sb-doped ZnO epitaxial films was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and the Hall-effect measurement. The measurement of the XRD phi-scan indicated that the epitaxial relationship between the ZnO:Sb layer and sapphire substrate was 1 1 2 ¯ 0 ZnO / / ( 1 1 ¯ 0 2 ) Al 2 O 3 and 1 1 ¯ 0 0 ZnO / / 1 1 2 ¯ 0 Al 2 O 3 . The out-of-plane a -axis lattice parameter of ZnO films was reduced monotonically with the increasing Sb doping level. The cross-sectional transmission electron microscopy (XTEM) observation confirmed the absence of any significant antimony oxide phase segregation across the thickness of the Sb-doped ZnO epitaxial film. However, the epitaxial quality of the films deteriorated as the level of Sb dopant increased. The electrical properties of ZnO:Sb film are closely correlated with post-annealing conditions and Sb doping concentrations.