Influence of Oxygen Deficiency on Surface Electronic Properties of Indium Tin Oxide Films

The unique bulk properties of indium tin oxide (ITO) are generally described by a high optical transparency over the visible spectrum and a low electrical resistivity. For some applications in opto-electronic devices, the surface properties of ITO often play an important role to determine the device performance. This work is to study the effect of oxygen deficiency on surface electronic properties of ITO. A set of ITO films with different carrier concentrations was fabricated by radio frequency magnetron sputtering using a hydrogen-argon gas mixture at a low temperature. The surface band bending of ITO films reflects the surface electronic properties and is also influenced by the carrier concentration in the bulk of the ITO films. The work function in highly oxygen deficient ITO films can be changed up to ∼0.3 eV when the hydrogen partial pressure changed from 0–3.2×10⁻³ Pa. It was manifested that barrier height at ITO/N,N′-bis(l-naphthyl)-N,N′-diphenyl-1,l′-biphentl-4,4′-diamine (NPB) interface can be adjusted from 0.56±0.05 eV to 0.87±0.05 eV, induced by oxygen deficiency in ITO films. This work demonstrated a possible approach to engineer the interfacial electronic properties at the ITO/organic interface desired for application in the efficient organic light-emitting diodes.