Ab initio study for adsorption and desorption behavior at step edges of GaN (0001) surface

The adsorption and desorption behavior of adatoms at step edges of GaN(0001) surface is investigated on the basis of ab initio calculations. Our calculations of single layer step edges along the [11(-)00] direction reveal that the structure of step edge depends on the growth condition. Furthermore, the adsorption behavior of Ga and N adatoms close to the step edges is found to be dependent on these structures. Under moderately Ga-rich and N-rich conditions, Ga adatoms are preferentially incorporated at the step edge with low adsorption energy (- 3.7 eV) and the Ehrlich-Schwoebel barrier (ESB) is recognized. On the other hand, the ESB for Ga adatoms is negligibly small under Ga-rich condition. These results suggest that island formation preferentially occurs away from single layer steps under Ga-rich condition, reasonably consistent with experimental results.