Experimental investigation of inclusion of hexagonal GaN phase-domain by varying nitrogen-beam direction to a (111) axis in MBE growth of cubic GaN

摘要

Crystalline quality of cubic phase (c-)GaN epilayers on (0 0 1) GaAs has been systematically investigated by varying nitrogen (N-) beam direction in molecular beam epitaxy. In this study, the N-beam was obliquely incident to the surface normal. The N-beam direction during both buffer layer and epilayer depositions could approximate either c-GaN[l 1 1]A or c-GaN[T 1 1]B. In the c-GaN epilayers grown with different N-beam directions, the c-GaN domain or hexagonal (h-)GaN domain showed the tilt and the mosaicity. From the X-ray rocking curves, the extraordinary c-GaN domains and the h-GaN domains were tilted by influence of oblique incidence of the N-beam. The phase purity of c-GaN domain became high when the N-beam direction was along a c-GaN[l 1 1]A direction during both the buffer layer and the epilayer depositions. In order to understand the difference in crystalline quality with change in the N-beam direction, we took account of stack of the Ga and N precursors on (1 1 1)A (or (1 1 1)B) c-GaN facet. It is considered that the difference of the crystalline quality result from the polarity of the facets.