A Theoretical Investigation of the Metastability of Al on a (100) Zinc Blende Substrate

The structural metastability of Al thin films on a (100) zinc blende substrate is discussed using cohesive energy calculations for bulk form and thin layers with both the pseudopotential perturbation approach and universal empirical potentials. In bulk form, face centered cubic (FCC) Al is more stable than body centered cubic (BCC) Al by 103 meV/atom. The total crystal energy, as a function of the (100) substrate lattice parameter, also indicates that FCC-Al is more stable structure over the lattice parameter range of semiconductor substrates with a zinc blende structure. In the epitaxial state, the stability of (110) FCC-Al equivalent to body centered tetragonal (BCT)-Al is found to be a competing phase. The planar energy difference between BCT- and FCC-Al is very small and is estimated to be 20 meV/atom at the interface between thin films and a substrate.