High mobility tungsten-doped indium oxide (IWO) deposited by room-temperature RF sputtering in pure argon plasma

Transparent conductive oxides (TCOs) are a key element in many applications, such as liquid crystal displays, organic light-emitting diodes and solar cells. In heterojunction solar cells they serve both as antireflective coatings and as conductive layers, so high mobilities along with low electron densities are necessary. Tungsten-doped indium oxide (IWO) grown by radio-frequency sputtering is a promising solution to meet all the above-mentioned requirements. In this work we show how a simple non-reactive room-temperature radio-frequency sputtering deposition followed by a low-temperature thermal annealing treatment allows producing IWO films with mobilities up to 70.9 cm/V⋅s and low carrier concentrations of 2-4 × 1020 cm−3, which result in resistivities as low as 2.5 × 10−4 Ω∙cm. We show that the sputtering damage to passivation can be recovered by a thermal treatment. A work function around 4.2 eV for most IWO films is also evaluated, which is a relevant parameter when applying the IWO as a TCO in solar cells. Possible effects of oxygen depletion in the target during deposition are also discussed.