Control of the crystalline quality of wurtzitic GaN films deposited on γ-LiAlO2 by ion-beam assisted molecular-beam epitaxy

Ion-beam assisted molecular-beam epitaxy was applied to deposit m-plane oriented wurtzitic gallium nitride films on γ-LiAlO2(1 0 0) substrates. The crystalline quality of the films was characterized by high resolution X-ray diffraction and transmission electron microscopy. The results show that in particular the nitrogen ion-to-gallium atom flux ratio is a crucial parameter influencing the growth direction and the crystalline quality of the GaN films on the (1 0 0) plane of γ-LiAlO2. Films deposited in the N-rich regime are exclusively m-plane oriented and exhibit a columnar morphology with a high mosaic spread and a rough surface. Films deposited in the Ga-rich regime are also exclusively m-plane oriented, but in contrast, they are of high crystalline quality and the surfaces are relatively smooth. Furthermore, extremely N-rich deposition conditions were found to lead to the formation of c-plane oriented wurtzitic GaN domains.