ELECTRONIC-STRUCTURE OF SILICON-NITRIDE STUDIED BY BOTH SOFT-X-RAY SPECTROSCOPY AND PHOTOELECTRON-SPECTROSCOPY

The valence and conduction band states of crystalline silicon nitride alpha-Si3N4 have been studied by using two complementary experimental methods. The total valence band distribution has been analyzed by x-ray induced photoelectron spectroscopy. The Si 3p valence states and the Si p conduction states have been probed selectively by x-ray emission and absorption spectroscopies, respectively. The experimental curves have been compared in the same energy scale referred to the Fermi level. Our results show clearly that the N 2ppi states of Si3N4 are located at the top of the valence band while Si 3p states, mixed to N 2p states and, respectively, to N 2s states are located at about E(F) - 8.4 eV and E(F) - 19.6 eV. Our experimental results are in very good agreement with theoretical simulations of the spectra made from recent density of states calculations by Robertson [Philos. Mag. B 63, 47 (1991)] in a tight binding approach.