Transparent conducting n-type ZnO:Sc – synthesis, optoelectronic properties and theoretical insight†
A joint theoretical-experimental study has been carried out for Sc-doped ZnO (SZO), one of the lesser-studied n-type transparent conducting oxide materials. Density functional theory has been used to create a computational model of SZO, in order to provide a theoretical basis for experimentally-observed phenomena where growth conditions, dopability and electronic properties are concerned. Meanwhile a range of thin films of SZO have been synthesised via chemical vapour deposition in an attempt to (i) observe experimentally the theoretically predicted properties, thereby providing mutual validation of the studies; (ii) seek the optimum dopant quantity for minimal electrical resistivity, and; (iii) demonstrate that transparent and electrically conductive SZO can be synthesised by chemical vapour deposition means. The films exhibit resistivities as low as ρ = 1.2 × 10−3 Ω cm, with carrier density n = 7.2 × 1020 cm−3 and charge carrier mobility μ = 7.5 cm2 V−1 s−1. Low resistivity of the films was retained after 12 months in storage under ambient conditions, indicating strong atmospheric stability. The films exhibit a high degree of transparency with 88% transmission in the visible range (400–750 nm). A correction to the Tauc method was applied to estimate band gaps of Eoptg = 3.45 ± 0.03 eV in the most conductive SZO sample and Eoptg = 3.34 ± 0.03 eV in nominally undoped ZnO.
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