Effects of sapphire (0001) surface modification by gallium pre-exposure on the growth of high-quality epitaxial ZnO film

ZnO films were grown on (0001) sapphire substrates using rf plasma-assisted molecular beam epitaxy. Distinct rotation domain structures were observed in ZnO films grown on Al-terminated or O-terminated sapphire surfaces. Therefore. the Ga preexposure process was adopted to modify the sapphire (0001) surface just before the buffer layer growth. It was revealed that the sapphire surface modification by Ga pre-exposure had significant effects on the elimination of the rotation domains in the ZnO epilayer. The full width at half maximum (FWHM) of the X-ray diffraction (XRD) rocking curve of the ZnO (002) reflection plane was as narrow as 67 arcsec. Consequently, a high-quality ZnO film with very good optical and electrical properties was obtained.