Crystallization of amorphous superlattices in the limit of ultrathin films with oxide interfaces

Annealing of amorphous Si/SiO2 or Ge/SiO2 multilayers produces nanocrystals embedded between oxide interfaces. It is found that the crystallization temperature is strongly enhanced by the presence of the oxide interfaces and follows an exponential law. The crystallization temperature increases rapidly with decreasing Si layer thickness, and a nonstoichiometric interface decreases the crystallization temperature compared to a stoichiometric interface of the same thickness. A model is presented that takes into account the interface energies, the thickness of the layer, the melting point of the system, and the crystallization temperature of the thick amorphous layer. The evidence for a critical crystallization radius and the influence of deviations from a perfect stoichiometric interface are discussed.