First-principle molecular-dynamics simulations of the sticking of Ga and N gas-phase atoms on wurtzite GaN surfaces Original Research Article

GaN is an important material of technological and fundamental interest. The first step to understand the growth of GaN thin films is to study the sticking properties of gas-phase Ga and N atoms on the GaN surface. Using first-principles molecular-dynamics simulations, we find that the Ga gas-phase atom moves very slowly onto the N-terminated GaN(0001) surface, while the N gas-phase atom moves very fast onto the Ga-terminated GaN(0001) surface. The incoming Ga atom is found to recoil at the first descent and then it drops down again toward the atop, H3, or T4 site depending on the initial condition. When the incoming N atom impinges on a Ga adatom or on the bridge site between two Ga adatoms, it is also found to recoil at the first descent. When it drops down again, it traverses to an opening in the Ga adlayer and penetrates down to the 1st N layer beneath. The incoming N atom eventually escapes back to vacuum when it initially impinges on a Ga adatom. When it initially impinges on the bridge site, it can traverse over a large distance and remains on the surface. Our results suggest that the incoming Ga atom is relatively inert, while the incoming N atom is very volatile. Our results also suggest that the sticking coefficient of N be much smaller than that of Ga.