Analysis of photoemission in amorphousSiOxandSiNxalloys in terms of a charge-transfer model

Shifts of the Si 2p, O 1s, and N 1s core-level spectra with the O or N content x for amorphous (a-) ${\mathrm{SiO}}_{\mathit{x}}$ and ${\mathrm{SiN}}_{\mathit{x}}$ films were examined by means of the effective-charge-analysis (ECA) model, in which the averaged partial charge ${\mathit{P}}_{\mathit{M}}$(x) (M=Si, O, or N) on a given atom is expressed as a function of x, by using Sanderson’s electronegativity results and the random-bonding model (RBM). The effective Si 2p binding energy ${\mathit{E}}_{\mathit{B}}$(Si 2p) was found to be linearly related to ${\mathit{P}}_{\mathrm{Si}}$(x) per single bond, ${\mathit{E}}_{\mathit{B}}$(Si 2p)=10.2${\mathit{P}}_{\mathrm{Si}}$(x)+99.3, independent of sample type. This equation predicts that addition of a unit of positive charge onto a Si atom shifts the Si 2p core level downward by 2.55 eV. Furthermore, the ECA model showed that spacing of the Si 2p lines due to five Si(${\mathrm{Si}}_{4\mathrm{-}\mathit{n}}$ ${\mathit{M}}_{\mathit{n}}$) (M=O or N) bonding units based on the RBM decreases with increasing n, in contrast to an assumption made by many workers. The evaluated negative partial charge, ${\mathit{P}}_{\mathrm{O}}$(x) or ${\mathit{P}}_{\mathrm{N}}$(x), on an O or N atom is found to decrease with increasing x, and the observed ${\mathit{E}}_{\mathit{B}}$(O 1s) and ${\mathit{E}}_{\mathit{B}}$(N 1s) are also linearly related to ${\mathit{P}}_{\mathrm{O}}$(x) and ${\mathit{P}}_{\mathrm{N}}$(x), respectively. Both the O 1s and N 1s core levels were shown to shift downward by around 1.2 eV as a unit negative charge is subtracted from the O and N atom.