BOND DENSITIES AND ELECTRONIC-STRUCTURE OF AMORPHOUS SINX-H

We present a study of amorphous hydrogenated silicon-nitrogen alloys (a-SiNx:H, 0 x<1.5) prepared by the rf reactive sputtering method. By combining results of x-ray photoemission spectroscopy, electron-energy-loss spectroscopy, and optical absorption, all the atom and bond densities and the kind and mean number of nearest neighbors of Si and N atoms are determined. For x<1, Si-N bonds increase at the expense of Si-Si bonds; N atoms are almost fully coordinated by three Si atoms, whereas Si atoms have N, H, and other Si atoms as nearest neighbors. For x>1, Si-N bonds increase at the expense of both Si-Si and Si-H bonds; however, this is not enough to saturate the three N valencies with Si and some N-H and possibly N-N bonds begin to appear. The opening of the optical gap occurs at x 1.1 when the ratio of the densities of Si-Si bonds to Si-N bonds has fallen below 0.10. Near stoichiometry, substantial amounts of Si-Si and N-H bonds are observed. The possibility of segregation into pure silicon and stoichiometric silicon nitride is discussed by analyzing the Si 2p line shape. A linear relationship between the Si 2p chemical shift and the mean number of N-atom nearest neighbors of Si is observed; a charge transfer of 0.35e per Si-N bond is determined. © 1990 The American Physical Society.