ZnO and ZnMgO growth on a-plane sapphire by molecular beam epitaxy

The growth of ZnO and ZnMgO alloy on a-plane sapphire substrates using an Epiquest-MBE system with an RF oxygen plasma cell was studied. Prior to growth, thermal treatment at 680/spl deg/C followed by oxygen plasma irradiation at 500/spl deg/C was performed for the improvement of the surface roughness of sapphire substrates. Then, ZnO layers with thickness of 0.6 /spl mu/m were grown in the range of 400-700/spl deg/C. Two factors were found for obtaining high quality layers. One is the use of a low temperature (250/spl deg/C) ZnO buffer layer and successive thermal treatment at high temperature (750/spl deg/C), which suppressed the formation of twin structure of subsequent layers. The other is the choice of growth temperature. The root mean square (RMS) roughness measured by atomic force microscopy (AFM) was minimized to 0.42 nm when growth temperature was 500/spl deg/C.