Monte Carlo simulations of phase separation during growth of semiconductor alloys

Monte Carlo simulations have been used to study the vapor phase growth of semiconductor alloys characterized by solid-phase miscibility gaps. Alloy phase separation occurred by a surface spinodal decomposition mechanism resulting in composition modulations in the plane of the film with a period of 2 to 5 nm. Decomposition was observed mainly within the spinodal region, but composition fluctuations persisted outside the spinodal. The amplitude of the composition modulations increased with increasing alloy interaction parameter but was kinetically limited over most of the parameter space investigated. This was indicated by the increased decomposition observed upon increasing the growth temperature T or decreasing the growth rate R. A strong dependence of decomposition on the surface reconstruction of the growing alloy films was also observed. In particular, stable surface dimers acted as traps for diffusing surface atoms, reducing the diffusion length and strongly limiting decomposition. Methods for minimizing decomposition are discussed.