Effect of low temperature thin GaN layer on ZnO film grown on nitridated c-sapphire by molecular beam epitaxy

A low-temperature thin GaN layer was used to wet the grown ZnO buffer layer effectively in the epitaxy of a ZnO film on a nitridated c-sapphire substrate by plasma-assisted molecular beam epitaxy. An atomically smooth Zn-polar ZnO epilayer was achieved with an rms roughness of 0.13 nm in a 3 mum x 3 mum scanned area. Triangular terraces with monolayer steps (0.26 nm) were observed by atomic force microscope. The crystalline quality of the ZnO epilayer was also improved with the full width at half maximum (FWHM) values for (002) and (102) omega-scans of 41 arcsec and 378 arcsec, respectively.