The Role of HiPIMS Pulse Length in Reactive Deposition of Transparent Conductive Oxide Nb:TiO₂ Films

The present paper sets out to investigate the role of voltage pulse length on the properties of Nb:TiO₂ films deposited by High Power Impulse Magnetron Sputtering (HiPIMS). Several characteristics of the films were investigated, namely, resistivity, transmittance, crystallinity and band gap values of Nb:TiO₂ films. Reactive depositions were carried out in Ar/O₂ plasma with 40 µs, 50 µs, 60 µs, and 70 µs pulses. Increasing the pulse length changes the deposition from compound to metal mode. As it gets closer to metal mode, the deposition rate increases by up to one order of magnitude, while the resistivity of the resulting Nb:TiO₂ film becomes as low as 10^-4 Ω.cm, without any significant loss in optical transmittance, which remains close to 90% for a wavelength around 450 nm, but reduction in 25% of heat transmission (above 800 nm) were observed. Results indicate the anatase phase for all deposition conditions, and Ti³⁺ states increase with the pulse length, which can be explained by the generation of a second band gap. Both the niobium doping and the Ti³⁺ states can contribute to increase the conductivity of the Nb:TiO₂ films in the as-deposited condition.

Keywords:
Titanium dioxide; Niobium; Resistivity; Optical properties; HiPIMS