ELECTRONIC-STRUCTURE OF AMORPHOUS GERMANIUM-NITROGEN ALLOYS - A UV PHOTOELECTRON-SPECTROSCOPY STUDY

The valence band and Ge3d core-level structure of amorphous germanium- nitrogen alloys (a-Ge1-xNx) of various compositions (0 < x < 0.36) hav e been studied by ultraviolet photoelectron spectroscopy using He I an d He II excitation. Two N-related bands centered at about 11 and 5 eV below the Fermi energy are found to evolve in the valence band spectra with increasing x. These are attributed to N2p bonding and lone-pair states, respectively. A systematic shift and broadening of the Ge3d co re level peaks occurs with increasing x. Analysis of this effect allow s for the determination of a N-induced chemical shift per Ge-N bond of 0.30 +/- 0.08 eV. For x > 0.22, a significant recession of the top of the valence band sets in, which is correlated by the sudden increase of the optical gap. An asymmetrical widening of the band gap for x > 0 .22 is deduced.