Electronic structure of amorphous Si-N compounds

We have measured valence-band photoemission spectra and dark conductivity of a-SiNₓ:H compounds for compositions between x=0 and x=1.35. The photoemission spectra have been measured with Zr M{ζ} and Al K{α} radiation of 151.4 and 1486.6 eV, respectively. At h{ν}=151.4 eV the spectra resemble directly the total density-of-states (DOS) of the system; the most important change with x is the shift of spectral weight from near the valence-band maximum (VBM) toward the center of the band, indicating the change from a band of Si-Si bonding states to a band of Si-N bonding states. At h{ν}=1486.6 eV the spectra are dominated by the contribution of the Si-3s partial DOS; this contribution is located at the bottom of the band and shifts toward higher binding energies with increasing x. We compare our results at x=0.36 and x=1.35 with those of two recent calculations. Combining results of the dark-conductivity measurements and the photoemission spectra with a previous determination of the optical gaps we make a plot of the VBM, Fermi-level position, and conduction-band minimum (CBM) versus x. It is shown that the sudden opening of the gap at x{~}1 is due mainly to the recession of the CBM.