Influence of the Oxygen Substoichiometry and of the Hydrogen Incorporation on the Electronic Band Structure of Amorphous Tungsten Oxide Films

The influence of the oxygen substoichiometry and of the hydrogen incorporation on the electronic structure of amorphous tungsten oxide films was investigated. It was found that both of them cause the appearance of intermediate bands (IBs) within the energy gap; approximately 3 and 1 eV below the edge of the conduction band (CB), respectively. The hydrogen is incorporated into the W-O network bonding either to the oxygen or to the tungsten ions. In the former case, the electronic structure of the material retains the characteristics of amorphous stoichiometric tungsten oxide with, additionally, the two IBs. In the latter case, the electronic structure of tungsten oxide is seriously perturbed because in addition to the IBs the Is orbitals of the hydrogen also contribute to the formation of the edges of valence and CBs causing the delocalization of electrons. Carriers donated by the incorporated hydrogen ions are excited in the CB, causing plasma oscillations and red shifting photoluminescence.