2, The University of Sydney, Camperdown, New South Wales, Australia
Indium tin oxide (ITO) is the most commonly used transparent conducting oxide (TCO) due to its high carrier mobility (up to ~100 cm2 V−1 s−1) and low absorption of visible-light. However, In-free TCOs have been sought for some time due to the cost and relative scarcity of In. Among these, alloys of ZnO and SnO2 (commonly referred to as ZTO) offer acceptable electron mobility (>10 cm2 V−1 s−1) and high thermodynamic stability . Importantly, the large diameter spherical orbitals of the Zn2+ and Sn4+ cations in ZTO cause the carrier mobility to be insensitive to structural disorder . Amorphous ZTO (a-ZTO), produced with low growth temperatures, therefore exhibits similar carrier mobility to its polycrystalline counterpart.
Here, we investigate the characteristics of a-ZTO deposited energetically using high power impulse magnetron sputtering (HiPIMS) . This technique has proved capable of producing high quality metal oxide layers suitable for electronic devices [3, 4]. Reactive co-deposition from Zn (HiPIMS mode) and Sn (DC magnetron sputtering mode) targets yielded a-ZTO with varying Zn:Sn composition across a 4-inch diameter sapphire substrate. The electrical and optical properties of this film were then studied as a function of composition. As-deposited, the films were amorphous, transparent and semi-insulating. Hydrogen (a known n-type dopant in ZnO and SnO2) was introduced into the a-ZTO by post-deposition annealing (1 h, 500 °C, 100 mTorr H2) and resulted in significantly increased conductivity with no measurable structural alterations. After annealing, Hall effect measurements revealed n-type carrier concentrations of ~1 × 1017 cm−3 and mobilities up to 15 cm2 V−1 s–1. These characteristics proved both stable and suitable for device applications. Results from transistors and memristors based on energetically deposited a-ZTO will be presented. These suggest that HiPIMS can produce dense, high quality a-ZTO suitable for electronic applications.
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