Paper EM-ThM6
Effects of Hydrogen Ambient and Film Thickness on ZnO:Al Electrical Properties

Thursday, October 18, 2007, 9:40 am, Room 612

Transparent conducting oxide (TCO) thin films are a vital part of flat-panel displays, electrochromic windows, and photovoltaic cells. ZnO-based TCOs may allow cost advantages compared to indium-containing TCOs such as indium tin oxide (ITO) or indium zinc oxide (IZO). Undoped ZnO and ZnO:Al (0.1, 0.2, 0.5, 1, and 2 wt.% Al₂O₃) films were deposited by RF magnetron sputtering. Controlled incorporation of H₂ in the Ar sputtering ambient, for films grown at substrate temperatures up to 200°C, results in mobilities exceeding 50 cm²V^-1s^-1 when using targets containing 0.1 and 0.2 wt.% Al₂O₃. Because high conductivity is achieved through high mobility at lower carrier concentration, these films demonstrate decreased infrared absorption compared to films containing the commonly used 2 wt.% Al₂O₃. ZnO:Al films grown in H₂ partial pressure (ZnO:Al:H) show no detectable changes in electrical properties during temperature-dependent Hall measurements conducted up to 170°C. Reduction in ZnO:Al mobility and carrier concentration with decreasing film thickness has been reported in the past, but mechanisms for these changes remain uncertain. Our studies show that ZnO:Al:H electrical properties are suboptimal if film thickness is less than ~300 nm. In attempts to improve the electrical properties of these thinner films, depositions were performed at room temperature with and without a 60-nm undoped ZnO nucleation layer. Results show that mobility values indeed benefit from this nucleation layer for film thicknesses less than 350 nm. However, films grown without the nucleation layer reached higher mobility values at thicknesses greater than 350 nm. This abstract is subject to government rights.