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Highly conducting (ρ = 3.9 × 10−4 Ωcm) and transparent (83%) polycrystalline Si-doped ZnO (SiZO) thin films have been deposited onto borosilicate glass substrates by pulsed laser deposition from (ZnO)1−x(SiO2)x (0 ≤ x ≤ 0.05) ceramic targets prepared using a sol-gel technique. Along with their structural, chemical, and optical properties, the electronic transport within these SiZO samples has been investigated as a function of silicon doping level and temperature. Measurements made between 80 and 350 K reveal an almost temperature-independent carrier concentration consistent with degenerate metallic conduction in all of these samples. The temperature-dependent Hall mobility has been modeled by considering the varying contribution of grain boundary and electron-phonon scattering in samples with different nominal silicon concentrations. [ABSTRACT FROM AUTHOR]

Fluoride in spray pyrolysis precursor solutions for silicon-doped zinc oxide (SiZO) transparent conductor thin films significantly improves their electrical conductivity by enhancing silicon doping efficiency and not, as previously assumed, by fluoride doping. Containing only earth-abundant elements, SiZO thus prepared rivals the best solution-processed indium-doped ZnO in performance. [ABSTRACT FROM AUTHOR]

We report a long-lasting enhancement in electrical properties occurs when zinc oxide (ZnO) thin films prepared by spray pyrolysis in a nitrogen atmosphere are treated with UV prior to the films' first exposure to air (here termed “in situ irradiation”). Carrier mobilities as high as 44.3 cm2 V−1 s−1– the highest values yet reported for any ZnO thin films made by spray pyrolysis – are exhibited by samples deposited at ca. 376 °C. In fact, such mobility values compare favorably with results that have been obtained using more complex, vacuum-based deposition techniques. The results of electrical, chemical, and microstructural characterization as a function of irradiation and deposition temperature indicate that the improved electrical properties stem from a modification of the relative populations of donor and acceptor defects at the grain boundaries of these polycrystalline films, allowing parallels to be drawn to the well-known phenomenon of “persistent” photoconductivity in ZnO. Finally, we consider how these observations about the interaction of ZnO with UV light relate to factors that limit the electrical performance of practical, transparent conducing oxide thin films. [ABSTRACT FROM AUTHOR]

We report a detailed investigation of the charge carrier transport in polycrystalline n-type impurity-doped zinc oxide (ZnO) thin films grown by spray pyrolysis over a wide range of carrier concentrations. Particular attention is devoted to a study of the composition-dependent metal-insulator transition (MIT) in this transparent conducting oxide (TCO). In order to describe the flow of electrons in these impurity-doped thin films over this full range of conditions, it is necessary to consider multiple electronic conduction processes. The first conduction process arises from current carriers thermally excited from impurity states into the (host) ZnO conduction band. The second involves thermally-activated, quantum-mechanical tunnelling within an impurity band located close to the host conduction band. The latter conduction process predominates at low temperatures whilst the former dominates at high temperatures. We find that a MIT occurs at a critical carrier concentration between 2 and 6 × 1019 cm-3. At higher concentrations in this metallic regime, the impurity band merges with the ZnO conduction band. The location of the MIT was determined from low temperature resistivity data and the results are discussed in terms of the Mott and Ioffe-Regel models. In addition, the overriding importance of grain boundaries is highlighted for these polycrystalline thin films; this is a key factor in determining and limiting electronic conduction in these samples, particularly at high temperatures. These results highlight the practical importance of understanding both the MIT and also grain boundary effects in determining the electrical performance of polycrystalline TCO films. [ABSTRACT FROM AUTHOR]