Growth parameter-property phase diagram for pulsed laser deposited transparent oxide conductor anatase Nb:TiO2
TL;DR: In this article, the structural and electrical properties of Nb:TiO2 thin films by varying the substrate temperature (TS) and oxygen partial pressure (PO2) were investigated.
Abstract: The authors performed a systematic study of the structural and electrical properties of Nb:TiO2 thin films by varying the substrate temperature (TS) and oxygen partial pressure (PO2). Niobium is found to incorporate easily and substitutionally into titanium lattice site as indicated by its low activation energy. By increasing TS, the carrier concentration (n) increases in the same way that niobium substitution fraction (s) increases, and the mobility increases as the structural quality is improved. With increasing PO2, n decreases dramatically though s does not change considerably. This may indicate that a large number of p-type native defects form, which “kill” the electrons produced by the Nb donors.
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TL;DR: In this paper, the development and properties of titanium dioxide (TiO 2 )-based transparent conducting oxides (TCO), which exhibit properties comparable to those of In 2-x Sn x O 3 (ITO), are reviewed.
Abstract: The development and properties of titanium dioxide (TiO 2 )-based transparent conducting oxides (TCO), which exhibit properties comparable to those of In 2-x Sn x O 3 (ITO), are reviewed in this article. An epitaxial thin film of anatase Ti 0.94 Nb 0.06 O 2 exhibited a resistivity (p) of 2.3 x 10 -4 Ω cm and internal transmittance of ~95% in the visible light region. Furthermore, we prepared polycrystalline films with p of 6.4 x 10 -4 Ω cm at room temperature on glass substrates by using sputtering. We focus on characteristics unique to TiO 2 -based TCO, such as a high refractive index, high transmittance in infrared, and high stability in reducing atmospheres. Possible applications of TiO 2 -based TCOs, as well as the mechanism of the transparent conducting properties found in this d-electron-based TCO, are discussed in this review.
142 citations
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TL;DR: Crystalline niobium-doped titania nanoparticles were synthesized via solvothermal procedures using tert-butyl alcohol as a novel reaction medium, and their assembly into mesoporous films was investigated.
Abstract: Crystalline niobium-doped titania nanoparticles were synthesized via solvothermal procedures using tert-butyl alcohol as a novel reaction medium, and their assembly into mesoporous films was investigated. The solvothermal procedure enables the preparation of crystalline doped and undoped nonagglomerated titania nanoparticles, whose size can be controlled from 4 to 15 nm by changing the reaction temperature and time. The anatase lattice of these particles can incorporate more than 20 mol % of Nb ions. The nanoparticles can be easily dispersed at high concentrations in THF to form stable colloidal suspensions and can be assembled into uniform porous mesostructures directed by the commercial Pluronic block copolymer F127. The resulting mesoporous films show a regular mesostructure with a d spacing of about 17 nm, a uniform pore size of about 10 nm with crystalline walls, a high porosity of 43%, and a large surface area of 190 m2 cm−3. Substitutional doping with niobium ions drastically increases the electric...
125 citations
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TL;DR: In this article, the authors investigated the electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means of first-principles band calculations and photoemission measurements.
Abstract: We have investigated electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means of first-principles band calculations and photoemission measurements. The band calculations revealed that Nb 4d orbitals are strongly hybridized with Ti 3d ones to form a d-nature conduction band, without impurity states in the in-gap region, resulting in high carrier density exceeding 1021 cm-3 and excellent optical transparency in the visible region. Furthermore, we confirmed that the results of valence band and core-level photoemission measurements are consistent with prediction by the present band calculations.
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TL;DR: In this article, the effect of Ag thickness on optical and electrical properties and the mechanism of conduction have been discussed, and the critical thickness of Ag mid-layer to form a continuous conducting layer is 9.5 nm and the multilayer has been optimized to obtain a sheet resistance of 5.7 Ω/sq and an average optical transmittance of 90% at 590 nm.
Abstract: Multilayer structures of TiO2/Ag/TiO2 have been deposited onto flexible substrates by room temperature sputtering to develop indium-free transparent composite electrodes. The effect of Ag thicknesses on optical and electrical properties and the mechanism of conduction have been discussed. The critical thickness (tc) of Ag mid-layer to form a continuous conducting layer is 9.5 nm and the multilayer has been optimized to obtain a sheet resistance of 5.7 Ω/sq and an average optical transmittance of 90% at 590 nm. The Haacke figure of merit (FOM) for tc has one of the highest FOMs with 61.4 × 10−3 Ω−1/sq.
83 citations
References
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TL;DR: Water photolysis is investigated by exploiting the fact that water is transparent to visible light and cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm.
Abstract: ALTHOUGH the possibility of water photolysis has been investigated by many workers, a useful method has only now been developed. Because water is transparent to visible light it cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm (ref. 1).
24,267 citations
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TL;DR: The observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8% is reported, indicating the existence of ferromagnetic long-range ordering.
Abstract: Dilute magnetic semiconductors and wide gap oxide semiconductors are appealing materials for magnetooptical devices. From a combinatorial screening approach looking at the solid solubility of transition metals in titanium dioxides and of their magnetic properties, we report on the observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8%. Magnetic microscopy images reveal a magnetic domain structure in the films, indicating the existence of ferromagnetic long-range ordering. The materials remain ferromagnetic above room temperature with a magnetic moment of 0.32 Bohr magnetons per cobalt atom. The film is conductive and exhibits a positive magnetoresistance of 60% at 2 kelvin.
2,238 citations
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TL;DR: The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper.
Abstract: The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper. The important TCO semiconductors are impurity-doped ZnO, In2O3 and SnO2 as well as multicomponent oxides consisting of combinations of ZnO, In2O3 and SnO2, including some ternary compounds existing in their systems. Development of these and other TCO semiconductors is important because the expanding need for transparent electrodes for optoelectronic device applications is jeopardizing the availability of indium-tin-oxide (ITO), whose main constituent, indium, is a very expensive and scarce material. Al- and Ga-doped ZnO (AZO and GZO) semiconductors are promising as alternatives to ITO for thin-film transparent electrode applications. In particular, AZO thin films, with a low resistivity of the order of 10−5 Ω cm and source materials that are inexpensive and non-toxic, are the best candidates. However, further development of the deposition techniques, such as magnetron sputtering or vacuum arc plasma evaporation, as well as of the targets is required to enable the preparation of AZO and GZO films on large area substrates with a high deposition rate.
1,834 citations
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TL;DR: In this article, the metastable phase anatase has been shown to have a wider optical absorption gap than rutile thin films, which is consistent with the high mobility, bandlike conduction observed in anatase crystals.
Abstract: Electrical and optical spectroscopic studies of TiO2 anatase thin filmsdeposited by sputtering show that the metastable phase anatase differs in electronic properties from the well‐known, stable phase rutile. Resistivity and Hall‐effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self‐trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.
1,456 citations