Growth kinetics of AlN and GaN films grown by molecular beam epitaxy on R-plane sapphire substrates

This paper reports the growth by molecular beam epitaxy of AlN and GaN thin films on R-plane sapphire substrates. Contrary to previous findings that GaN grows with its (11(2) over bar0) A-plane parallel to the (1 (1) over bar 02) R-plane of sapphire, our results indicate that the crystallographic orientation of the III-nitride films is strongly dependent on the kinetic conditions of growth for the GaN or AlN buffer layers. Thus, group III-rich conditions for growth of either GaN or AlN buffers result in nitride films having (11 (2) over bar0) planes parallel to the sapphire surface, and basal-plane stacking faults parallel to the growth direction. The growth of these buffers under N-rich conditions instead leads to nitride films with (11 (2) over bar6) planes parallel to the sapphire surface, with inclined c-plane stacking faults that often terminate threading dislocations. Moreover, electron microscope observations indicate that slight miscut (similar to 0.5 degrees) of the R-plane sapphire substrate almost completely suppresses the formation of twinning defects in the (11 (2) over bar6) GaN films. (C) 2010 American Institute of Physics. [doi :10.1063/1.3475521]