Electronic structure of amorphous germanium-nitrogen alloys: a UV photoelectron spectroscopy study

Abstract

The valence band and Ge 3d core-level structure of amorphous germanium-nitrogen alloys (a-Ge 1− x N x ) of various compositions (0 < x < 0.36) have been studied by ultraviolet photoelectron spectroscopy using HeI and HeII 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 Ge 3d core level peaks occurs with increasing x. Analysis of this effect allows 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.