Symmetry and passivation dependence of the optical properties of nanocrystalline silicon structures

The electronic and optical properties of Si-based quantum wells (QW's) are studied ab initio by means of the linear-muffin-tin-orbital (LMTO) method in order to investigate their dependence on the symmetry of the lattice and on the passivating species that saturates the Si dangling bonds. We find that the symmetry of the lattice changes the nature of the gap that is indirect in the Si-H(111) saturated QW's and becomes direct in the Si-H(001) saturated QW's. The saturating species play instead an important role in the formation of interface states that can occupy or leave free the band gap so improving or making worse the optical properties of the material. Studying the Si-SiO2(001) superlattice we found that oxygen related defects play an important role in the determination of the optoelectronic properties of the material. (C) 2000 Elsevier Science S.A. All rights reserved