Density functional theory analysis of SiO2-oxynitride interfaces

Two different interface models for crystalline oxynitride on SiO
₂
are proposed and investigated. The two models are proposed to model oxynitride gate stacks on Si substrate with SiO
₂
as the interlayer film. State-free insulating interfaces were obtained by expanding the bulk oxynitride cell by approximately 12% and 1% to match the lattice constant of SiO
₂
along the [100] and [010] axis respectively. The results that were obtained demonstrate state-free insulating interfaces for the two models with, however, valence band offsets of 0.1eV and 1.45 eV respectively. The significant decrease in the valence band offsets is attributed mainly to the significant expansion of the oxynitride's lattice constant to lattice-match (001)SiO
₂
, as well as, to the high concentration of nitrogen atoms in the interface.