Effect of the Oxygen Sub-Stoichiometry and of Hydrogen Insertion on the Formation of Intermediate Bands within the Gap of Disordered Molybdenum Oxide Films

Abstract

The electronic structure of disordered-amorphous molybdenum oxide films was investigated near the band gap by optical absorption and photoluminescence (PL) measurements. It was found that, in nearly stoichiometric films, the 3.2 eV wide gap is free of states and a PL band at 3.7 eV was attributed to electronic transitions between the Mo 4d bonding–antibonding orbitals. In sub-stoichiometric films, electronic states appear within the gap giving rise to additional PL emission within the range 3–3.25 eV. The band gap remains at 3.2 eV, and intermediate bands (IB) are formed within the gap for oxygen-deficient hydrogenated samples. A substantial increase of the PL intensity within the range 2.75–3.75 eV was observed, attributed to the IBs and the increase of the density of Mo 4d antibonding states within the conduction band (CB). The band gap decreases to 2.7 eV in sub-stoichiometric and hydrogenated samples, while the rest of the elctronic structure remains unchanged as for hydrogenated samples also giving e...