The Effect of Sub-Oxide Phases on the Transparency of Tin-Doped Gallium Oxide

There have been a number of studies on the fabrication of Sn-doped gallium oxide (Ga₂O₃:Sn) films with both conductive and transparent properties using a variety of deposition methods. However, often, synthesis results in films that are not transparent. In this paper, we examine the mechanisms underlying these results in Ga₂O₃:Sn thin films prepared at various growth temperatures, Sn concentrations, and oxygen partial pressures. With X-ray absorption spectroscopy, transmission electron microscopy and energy dispersive spectroscopy, we find that when films are grown under the oxygen deficient conditions there are Ga sub-oxide and SnO_x phases in the Ga₂O₃:Sn thin film. These Ga sub-oxide phases are only found in non-transparent films, and so we infer that the Ga sub-oxide is responsible for the non-transparency. These observations suggest that to obtain transparent Ga₂O₃:Sn, films deposition or subsequent annealing must be carefully controlled in both temperature and oxygen partial pressure to avoid the formation of Ga sub-oxide phases.