We present a study of amorphous hydrogenated silicon-nitrogen alloys (a-SiN":H, O~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, SiN 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, SiN 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 SiN 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 SiN bond is determined. I. INTRODUCTION Silicon nitride is a material widely used in the ceramic and microelectronic industries. This has prompted a number of studies conducted to obtain silicon nitride by different methods and to determine its structural and electrical properties. It is mostly prepared as thin amorphous films which, in general, are nonstoichiometric and contain H in concentrations between 10 at. % and 40 at. %. Aiyama et al. ' and Misawa et al. have studied the amorphous structure of near-stoichiometric compounds by x-ray and neutron diffraction, finding that the shortrange order strongly resembles that of the crystalline forms. The electronic structure of a-SiN, in the range 0~x (2, has been the subject of a very complete investigation performed by Karcher et al. using x-ray photoelectron spectroscopy (XPS). They thoroughly analyzed the valence bands and obtained some information about the SiN bonding by deconvoluting the Si 2p peak. Densities of electron states of the crystalline and amorphous forms have been calculated by Ren and Ching,

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