ELECTRONIC-STRUCTURE OF AMORPHOUS SI-N COMPOUNDS

We have measured valence-band photoemission spectra and dark conductivity of a-SiN(x):H compounds for compositions between x = 0 and x = 1.35. The photoemission spectra have been measured with Zr Mzeta and Al Kalpha radiation of 151.4 and 1486.6 eV, respectively. At hnu = 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 hnu = 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 approximately 1 is due mainly to the recession of the CBM.