  An unusual growth mechanism of metastable zincblende AlN thin film by
diffusion of nitrogen atoms into Al lattice is established. Using
first-principles density functional theory, we studied the possibility of
thermodynamic stability of AlN as a zincblende phase due to epitaxial strains
and interface effect, which fails to explain the formation of zincblende AlN.
We then compared the formation energetics of rocksalt and zincblende AlN in fcc
Al through direct diffusion of nitrogen atoms to Al octahedral and tetrahedral
interstitials. The formation of zincblende AlN thin film is determined to be a
kinetically driven process, not a thermodynamically driven process.
