Competitive growth mechanisms of aluminum nitride thin films deposited by off-normal reactive magnetron sputtering

We have recently shown that AlN (0002) (c axis) is tilted abruptly toward the deposition direction as N(2) concentration is increased in N(2)/Ar sputtering gas mixtures. Here, we present a Monte Carlo simulation model to describe the phenomenon of sudden c-axis AlN tilt. The model is based on the assumption that AlN islands with their c axis parallel to substrate normal and AlN islands with tilted c axis coexist at the initial stages of the growth and they can provide the adatoms with different surface mobilities. It is believed that the adatom mobilities are quenched when N(2) concentration reaches a certain amount in the reactive sputtering of AlN. Our model further assumes that adatom mobility differences on different islands result in a growth rate difference of the islands. At the initial stages of the growth, AlN islands with tilted c axis grow taller due to the lower adatom mobility on these islands. As they grow taller, they win the competition and stop the further growth of AlN islands with their c axis parallel to substrate normal due to shadowing effect. Monte Carlo simulations revealed that the shadowing effect combined with different adatom mobilities promotes the sudden c-axis tilt in AlN thin films. (C) 2008 American Institute of Physics.