Synthesis of conductive and transparent Nb-doped TiO 2 films: Role of the target material and sputtering gas composition (original) (raw)
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Structural and electrical properties of Nb-doped TiO2 films sputtered with plasma emission control
Thin Solid Films, 2014
A technique to deposit Nb-doped films of TiO 2 by radio-frequency magnetron sputtering was investigated. Nb wires are put onto the sputter track of a metallic titanium target and the oxidation state of the target is controlled by the intensity of a Ti line from the plasma emission. The sputtered films are analyzed with X-ray diffraction, RBS (Rutherford back scattering), energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and SEM (scanning electron microscopy). After post-heating at 400°C, all films exhibit the anatase structure. The films are polycrystalline with a Nb/[Nb + Ti] content from 2 to 17 at.%. RBS and SEM indicate that the films consist of two sub-layers with the surface layer containing more Nb and exhibiting a clearer columnar structure. There is an optimum oxidation state of the target in the transition region between metallic and oxidic modes where the lowest resistivity of 7 × 10 −4 Ωcm is achieved. Nb is incorporated as Nb 5+ into the anatase lattice, but in suboptimal films, Ti vacancies (acceptors) may compensate the donor effect of Nb. The oxygen content in the films is higher than for stoichiometric TiO 2 . O interstitials may increase the mass density of the films. The lattice parameter a and the unit cell volume increase with the Nb content in a similar manner as observed for single crystals of TiO 2 :Nb.
Transparent and Conducting TiO2 : Nb Thin Films Prepared by Spray Pyrolysis Technique
American Research Journal of Physics, 2015
To date, only sputtering and pulsed laser deposition (PLD) techniques have been employed successfully to fabricate highly conducting and transparent TiO 2 :Nb (TNO) films. In this article, we demonstrate that transparent and conducting Nb : TiO 2 films can be made by the spray pyrolysis technique. The films were deposited on Corning 7059 glass substrates at 500 15˚C using an alcoholic precursor solution consisting of titanium (iv) isopropoxide and 5 NbCl. The influence of increasing Nb concentration on the electrical, optical and structural properties was investigated. The minimum resistivity, 3.36-3 10 Ω cm, for 2 x x-1 O Nb Ti film (x = 0.15) was obtained after 1 hour post deposition annealing in hydrogen atmosphere at 500˚C. The x-ray diffraction of hydrogen annealed films showed a polycrystalline anatase (004)-oriented phase without any second phases. The optical band gap for undoped and doped films lay in the range 3.38-3.47 eV. Using dispersion analysis, optical constants were determined from spectro-photometric measurements for films on glass.
Influence of Thermal Treatment on Electrical Properties of Transparent TiO 2 :Nb Thin Films
Proc. 39th Int. Spring Seminar on Electronics Technology, Pilsen (Czechia), 2016
This study presents electrical behavior of TiO 2 :Nb thin films with niobium concentration up to 13 at. %. The layers were deposited on Corning 7059 glass substrates by unipolar dc pulse magnetron co-sputtering from TiO 2 and Nb composite target. Manufactured films underwent thermal treatment in the ambient air up to the 873 K. Dependencies between the temperature and electrical conductivity as well as thermoelectric force were determined within the range of 300-578 K. An amorphous TiO 2 :Nb films with optical transparency of about 50% in the visible range and resistivity higher than 8 Ωcm were achieved directly after deposition for the target power density discharge in the range of 4.7-5.8 W/cm 2. During the post process air thermal treatment a rapid resistivity decrease (over 1000) was observed up to final value of 1.5×10-3 Ωcm at 300 K. Moreover the conversion from n-type semiconductivity to metallic conductivity was observed.
Thin Solid Films, 2018
Oxide-based films and nanostructures have emerged as important materials for a wide range of applications such as photovoltaics, optoelectronics, gas sensing and electronics. To develop an appropriate understanding of the properties of these oxides, it is necessary to address the material preparation methods and defect probing issues. This work reports on the synthesis processes of TiO 2 based transparent conductive films, their stoichiometry control and defect identifying, in relation with their electrical and optical properties. Un-doped and TiO 2 :Nb films were deposited by RF co-sputtering from TiO 2 and Nb 2 O 5 targets in Ar plasma. The chemical species present in the plasmas used in deposition process were investigated by optical emission spectroscopy, which was later on correlated with the defects structure of the films. Analysis by X-ray photoelectron spectroscopy shed more light on the nature of the vacancies and on the effect of the latter on the optical and electrical properties of the films. In terms of results, we measured electrical resistivity in the range 10-2-10-3 Ω.cm for the intrinsically and extrinsically doped films (films doped with oxygen vacancies and Nb +5 respectively) while the lowest resistivity was obtained for intrinsically-extrinsically co-doped TiO 2 films (7.4×10-4 Ω.cm). The films transparency was also actively determined by the defects in the lattice and highly transparent films (65-85 % in the visible range) were obtained by controlling the density of defects. The approach adopted in this work for the generation of oxygen vacancies could be useful for other oxide-based films, where the oxygen vacancies-dependent properties are crucial, for room temperature ferromagnetism and photocatalytic applications.
Influence of thermal treatment on electrical properties of transparent TiO2:Nb thin films
2016 39th International Spring Seminar on Electronics Technology (ISSE), 2016
This study presents electrical behavior of TiO2:Nb thin films with niobium concentration up to 13 at. %. The layers were deposited on Corning 7059 glass substrates by unipolar dc pulse magnetron co-sputtering from TiO2 and Nb composite target. Manufactured films underwent thermal treatment in the ambient air up to the 873 K. Dependencies between the temperature and electrical conductivity as well as thermoelectric force were determined within the range of 300-578 K. An amorphous TiO2:Nb films with optical transparency of about 50% in the visible range and resistivity higher than 8 Ωcm were achieved directly after deposition for the target power density discharge in the range of 4.7-5.8 W/cm2. During the post process air thermal treatment a rapid resistivity decrease (over 1000×) was observed up to final value of 1.5×10-3 Qcm at 300 K. Moreover the conversion from n-type semiconductivity to metallic conductivity was observed. Simultaneously the layers exhibited the substantial increase in the transparency and decrease in Seebeck coefficient from -160 μV/K to -35 μV/K. Electrical behavior of the films where examined with the use of NiCrSi/Ag thin films contacts pads according to Kelvin method.
Materials Research Bulletin, 2016
A technique to deposit Nb-doped films of TiO 2 by radio-frequency magnetron sputtering was investigated. Nb wires are put onto the sputter track of a metallic titanium target and the oxidation state of the target is controlled by the intensity of a Ti line from the plasma emission. The sputtered films are analyzed with X-ray diffraction, RBS (Rutherford back scattering), energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and SEM (scanning electron microscopy). After post-heating at 400°C, all films exhibit the anatase structure. The films are polycrystalline with a Nb/[Nb + Ti] content from 2 to 17 at.%. RBS and SEM indicate that the films consist of two sub-layers with the surface layer containing more Nb and exhibiting a clearer columnar structure. There is an optimum oxidation state of the target in the transition region between metallic and oxidic modes where the lowest resistivity of 7 × 10 −4 Ωcm is achieved. Nb is incorporated as Nb 5+ into the anatase lattice, but in suboptimal films, Ti vacancies (acceptors) may compensate the donor effect of Nb. The oxygen content in the films is higher than for stoichiometric TiO 2. O interstitials may increase the mass density of the films. The lattice parameter a and the unit cell volume increase with the Nb content in a similar manner as observed for single crystals of TiO 2 :Nb.
Journal of Materials Science: Materials in Electronics, 2016
Pure and Nb doped TiO 2 (TNO) thin films were deposited onto glass substrates by RF magnetron sputtering technique using a Nb and TiO 2 mixture powder target at room temperature to explore the possibility of producing sputtered TNO films by a low cost process. The effect of Nb doping on the structure, morphology, optical and electrical properties of the prepared films was studied by systematically varying the Nb content from 2 to 6 wto/o. GXRD results show that the deposited films mainly possess rutile phase with the (110) orientation. Raman spectra confirm that the deposited films are predominantly rutile phase. Surface roughness increases with the increase of Nb doping concentration , which may be attributed to the structural changes in the film due to the incorporation of Nb into the TiO 2 lattice. Optical transmittance in the vis ible range reaches 85 % for the undoped films then it decreases as the doping content increases. Doping by nio bium resulted in a slight increase in the optical band gap energy of the films due to the Burstein-Moss effect. The resistivity measurement of TNO films reveals that the Nb doping improves the electrical conductivity of the depos ited films compared to the undoped one. The best value was observed for films deposited at 4 wto/o Nb.
Materials Research, 2019
Niobium doped dititanium trioxide (Ti 2 O 3 :Nb) films were deposited on glass substrates, through grid-assisted magnetron sputtering. The Ti 2 O 3 :Nb films were characterized by X-ray diffraction (XRD), electrical conductivity and optical properties. Film deposition was carried out in two different substrate bias modes: DC and unipolar pulsed. Results show that the negative-pulsed mode improves conductivity and crystallinity. The XRD results show peaks corresponding crystallographic planes of Ti 2 O 3. No niobium oxide Nb x O y peaks were observed, which indicates that niobium oxide if formed, is amorphous, and/or substituted Nb atoms remain in a solid solution within the Ti2O3 structure. It was observed that "as-deposited" Ti 2 O 3 :Nb films (without post annealing) are transparent and electrical conductive, with transmittance that reaches 60% in the visible light wavelength despite the considerable thickness of the film and a miminum resistivity of 2x10-2 Ω.cm which indicates that there is potential for application as Transparent Conductive Oxide (TCO).
The Role of HiPIMS Pulse Length in Reactive Deposition of Transparent Conductive Oxide Nb:TiO2 Films
Materials Research-ibero-american Journal of Materials, 2023
The present paper sets out to investigate the role of voltage pulse length on the properties of Nb:TiO 2 films deposited by High Power Impulse Magnetron Sputtering (HiPIMS). Several characteristics of the films were investigated, namely, resistivity, transmittance, crystallinity and band gap values of Nb:TiO 2 films. Reactive depositions were carried out in Ar/O 2 plasma with 40 µs, 50 µs, 60 µs, and 70 µs pulses. Increasing the pulse length changes the deposition from compound to metal mode. As it gets closer to metal mode, the deposition rate increases by up to one order of magnitude, while the resistivity of the resulting Nb:TiO 2 film becomes as low as 10-4 Ω.cm, without any significant loss in optical transmittance, which remains close to 90% for a wavelength around 450 nm, but reduction in 25% of heat transmission (above 800 nm) were observed. Results indicate the anatase phase for all deposition conditions, and Ti 3+ states increase with the pulse length, which can be explained by the generation of a second band gap. Both the niobium doping and the Ti 3+ states can contribute to increase the conductivity of the Nb:TiO 2 films in the as-deposited condition.
Conducting Nb-doped TiO2 thin films fabricated with an atomic layer deposition technique
Thin Solid Films, 2014
Highly conducting Ti 1 − x Nb x O 2 thin films have been grown on glass substrates from TiCl 4 , Nb(OEt) 5 and H 2 O with an atomic layer deposition (ALD) technique. The films become electrically conducting and crystallize with the anatase structure upon a reductive post-deposition annealing. A highly c-axis oriented Ti 0.75 Nb 0.25 O 2 film exhibits room-temperature resistivity as low as 1.4 × 10 −3 Ω cm. The charge carrier density and electron mobility, as estimated from Seebeck and resistivity measurements, are 0.21-1.1 × 10 21 cm −3 and 4.2-22 cm 2 /Vs, respectively. The electrical properties of the ALD-fabricated Nb-doped anatase films are comparable with those of sputter-deposited polycrystalline films on glass.