Reactive close field unbalance magnetron sputter deposition of titanium dioxides for potential photovoltaic applications

In this paper, crystallised TiO2 thin film was produced by reactive Closed Field UnBalanced Magnetron Sputter Ion Plating. Various deposition conditions were studied, including sputtering power, oxygen partial pressure and elemental doping and their effects on the resulting titania structure were characterised. Rutile or anatase titania can be obtained selectively or in combination by properly controlling the deposition conditions, i.e. rutile structure can be obtained using one titanium target with high oxygen flow (20% OEM) and be enhanced by manganese doping, and fully anatase structure can be formed by preheating the sample with an auxiliary heater and heating the sample in the reactive sputtering process. TiO2 has a wide band gap (3.2 eV for anatase and 3.0 eV for rutile) which limits its ability to absorb the light to the ultraviolet region. N and/or Mn doping in the thin titanium dioxide films was used to narrow the band gap of TiO2 to about 2.0 eV with improved electrical properties.