Peak Position of Photoluminescence of Si Nanocrystals versus Thickness of SiO_x Thin Films

Peak position of photoluminescence (PL) of Si nanocrystals was found to change in an exponential decay form with the increasing thickness of SiO_x (0 < x < 2) thin films. The results were interpreted in terms of a model modified from the theory of Zacharias-Streitenberger Phys. Rev. B 62 (2000) 8391 from an energetic viewpoint. It was inferred from our model that under certain conditions regarding the energies of interfaces between the substrate and Si clusters and between the matrix and the Si clusters, the farer the Si cluster away from the substrate, the larger the nc-Si size until saturation is reached. This conclusion explains our PL observations according to the quantum confinement effect.