Origin of the tilt of crystalline axis influenced by the N-beam incidence direction in rf-MBE of cubic GaN epilayer on (001) GaAs

We found that the direction of the [001] axis of the c-GaN epilayer grown on (001) GaAs was slightly tilted towards the direction of the N-beam during the epitaxial growth by rf-MBE, where the N-beam was incident obliquely to the surface normal. When the tilt of the c-GaN [001] axis was observed, the typical X-ray rocking FWHM value for (002) c-GaN was about 60 arcmin. This indicates that the large mosaicity is related to the tilt of the c-GaN [001] axis. Because the tilt is easily observed for the c-GaN epilayers grown at high growth rate, this implies that the large amount of N species on the growing surface is the origin of the tilt of c-GaN [001] axis. As for the inclusion of the h-GaN phase domain, we found that the peak shifts for the (1011) h-GaN planes occurred in accordance with the peak shift of (002) c-GaN in reciprocal space mappings.