Study of the electronic structure of a-Si1-yNiy:H alloys by XPS and XES

An investigation is reported of the electronic structure of amorphous films of hydrogenated silicon-nickel alloys, a-Si1-yNiy:H, by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. The former technique provides the binding energy of Si 2p, Ni 2p and Ni 3p core levels in addition to the valence band density of states. The latter yields the partial density of states related to Si 3p and Ni 3d. Changes in the core-level binding energies and in the valence-band structure have been studied as the nickel concentration in the alloys is increased through the semiconductor-to-metal transition. The uppermost valence band changes from Si 3p to Ni 3d character and moves upward in energy, eventually leading to a finite density of (extended) states at the Fermi level. The results are discussed in the light of previous studies on similar films of the optical and electrical properties and with reference to theoretical calculations on crystalline nickel silicides.