Microstructural and optical properties of Ta-doped ZnO films prepared by radio frequency magnetron sputtering
Introduction
Zinc oxide (ZnO) has drawn many attention due to its excellent physical properties such as large exciton binding energy (60 meV), excellent transparency in the visible range, wide direct band gap (∼3.37 eV), and high piezoelectric constant. It has potential applications in gas sensors, UV lasers, surface acoustic wave devices, and film bulk acoustic resonators. The properties of ZnO can be improved and the range of its applications can be expanded by doping different foreign elements into ZnO. ZnO doped with group III elements such as Al, Ga, and In shows enhanced conductivity and can be used as a transparent conducting oxide (TCO) [1], [2], [3], [4], [5]. ZnO doped by transition elements such as Co, Mn and Fe exhibits ferromagnetic (FM) behavior and can be used as a dilute magnetic semiconductor (DMS) in spintronics devices [6], [7], [8], [9], [10]. Furthermore, p-type ZnO is produced by doping ZnO with N, P or Sb elements [11], [12], [13] for use in the blue and ultraviolet solid-state light emitters and detectors. Additionally, the use of doped ZnO can improve the gas sensor selectivity due to the specific interactions between the molecules to be detected and the ions in the sensing materials [14], [15], [16].
The efficiency of the dopant element is related to its electronegativity as well as to the difference between its ionic radius and the ionic radius of Zn [17]. Ta is an efficient doping element for ZnO due to the high valence difference between Ta+5 (or Ta+4, Ta3+) ions and substituted Zn+2 ions. Therefore, a very small amount of Ta dopant can provide enough free carriers and reduce the ion scattering effect [18]. Moreover, the ionic radii of Ta5+ (0.064 nm), Ta4+ (0.068 nm), and Ta3+ (0.072 nm) are close to the radius of Zn2+ (0.074 nm); thus, it is theoretically possible for Ta to substitute for Zn in the ZnO lattice. However, there are only a few reports in the literature on Ta-doped ZnO films [17], [18], [19], and to the best of our knowledge, many properties of Ta-doped ZnO film, for example luminescence, have not yet been studied systematically.
In this study, we prepared Ta-doped ZnO films with various Ta contents by RF magnetron sputtering. The composition, morphology, microstructure, optical and photoluminescence properties of Ta-doped ZnO films were investigated.
Section snippets
Preparation of Ta doped ZnO films
Ta-doped ZnO films have been deposited on Si and glass substrates by radio frequency magnetron sputtering. ZnO ceramic (purity: 99.99%, diameter: 6 cm, thickness: 3 mm) was used as the sputtering target. High purity (99.99%) Ta metallic wires, with a diameter of 1.5 mm and a length of 6 cm, were hung above the ZnO target and served as the dopant source. The doping amount was controlled by changing the number of Ta wires. The number of Ta wires varied from 1 to 5 and the corresponding samples were
Results and discussions
The prepared films were analyzed by EDS to identify their compositions with the results shown in Fig. 1(a). Only three elements (Zn, O and Ta) are found in the films. Fig. 1(b) shows the atomic percent contents of the three elements in Ta-doped ZnO films. Ta atomic percent is 0 at% for S0, 0.34 at% for S1, 0.97 at% for S2, 2.02 at% for S3, 3.32 at% for S4, and 5.02 at% for S5. Zn fraction decreases from 46.20 at% to 37.14 at% and the O atom fraction slightly increases from 53.80 at% to 57.84 at% as the
Conclusion
Un-doped and Ta-doped ZnO films have been prepared by radio frequency magnetron sputtering. Ta content in the ZnO films measured by EDS is in the range of 0–5.02 at%. The surface morphology, microstructure, optical and photoluminescence properties of the prepared films were studied. The results show that the grain size, film thickness and surface roughness of the prepared films decrease with increasing Ta doping concentration from 0 at% to 3.32 at%. The smallest RMS roughness is 0.56 nm for the ZnO
Acknowledgments
This study was supported by the National Natural Science Foundation of China (Nos. 61504096, 61401306, 61301045 and 61306010), the Natural Science Foundation of Tianjin City (Nos. 13JCZDJC36000 and 15JCYBJC24000), the Excellent Young Teachers Program of Tianjin, and the Youth Top-notch Talents Program of Tianjin.
References (40)
- et al.
Optimisation of ZnO: Al films by change of sputter gas pressure for solar cell application
Appl. Surf. Sci.
(2002) - et al.
Transparent conducting ZnO: Al, In and Sn thin films deposited by the sol-gel method
Thin Solid Films
(2003) - et al.
Optical and electrical characteristics of aluminum-doped ZnO thin films prepared by solgel technique
J. Cryst. Growth
(1998) - et al.
Influence of the deposition pressure on the properties of transparent and conductive ZnO: Ga thin-film produced by r.f. sputtering at room temperature
Thin Solid Films
(2003) - et al.
Low resistivity transparent conducting Al-doped ZnO films prepared by pulsed laser deposition
Thin Solid Films
(2003) - et al.
Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films
Mater. Sci. Eng. R
(2008) - et al.
Pulsed laser reactive deposition of p-type ZnO film enhanced by an electron cyclotron resonance source
J. Cryst. Growth
(2001) - et al.
Nano-crystalline Cu-doped ZnO thin film gas sensor for CO
Sens. Actuators B – Chem.
(2006) - et al.
Sensing characteristics of tin-doped ZnO thin films as NO2 gas sensor
Sens. Actuators B – Chem.
(2005) - et al.
Gas sensitivity of ZnO based thick film sensor to NH3 at room temperature
Sens. Actuators B – Chem.
(1999)
Effects of thermal treatment on the characteristics of boron and tantalum-doped ZnO thin films deposited by the electrospraying method at atmospheric pressure
Surf. Coat. Technol.
Preparation, microstructure and photoelectrical properties of Tantalum-doped zinc oxide transparent conducting films
J. Alloy. Compd.
Effects of doping concentration and annealing temperature on properties of highly-oriented al-doped ZnO films
J. Cryst. Growth
Structural, optical, spectroscopic and electrical properties of Mo-doped ZnO thin films grown by radio frequency magnetron sputtering
Thin Solid Films
Structural, optical and visible light photocatalytic properties of nanocrystalline Nd doped ZnO thin films prepared by spin coating method
Ceram. Int.
Effects of Na content on structural and optical properties of Na-doped ZnO thin films prepared by sol–gel method
J. Alloy. Compd.
Optical and gas sensing properties of Al-doped ZnO transparent conducting films prepared by sol-gel method under different heat treatments
Ceram. Int.
Enhancing the electrical parameters of ZnO films deposited using a low-cost chemical spray technique through Ta doping
J. Alloy. Compd.
Fabrication of tantalum oxide layers onto titanium substrates for improved corrosion resistance and cytocompatibility
Surf. Coat. Technol.
Electrooxidation of methanol and ethanol in acidic medium using a platinum electrode modified with lanthanum-doped tantalum oxide film
Electrochim. Acta
Cited by (27)
Investigations on electronic properties and optical properties of Zn<inf>9-x</inf>Ag<inf>x</inf>O/G based on first-principles
2022, Materials Science in Semiconductor ProcessingA first-principles study on electronic and optical properties for Zn<inf>31-x</inf>Al<inf>x</inf>MgO
2021, Physica B: Condensed MatterO<sup>2-</sup> enhancement and recombination delay through Ta+gC<inf>3</inf>N<inf>4</inf> addition with ZnO for effective photocatalytic dye decomposition
2020, Surfaces and InterfacesCitation Excerpt :In this context, tantalum (Ta) (one of the compatible doping metal) [11] - and graphitic carbon nitride (g-C3N4) are added with ZnO in this study. The ionic radius of Ta5+ (0.064 nm) is close to that of Zn2+ (0.074 nm) and it is reported that Ta is one of the best dopants for improving the photocatalytic ability of ZnO when compared with the other transition metals [12]. Similarly, g-C3N4 is one of the carbonaceous materials having smaller band gap which can extend the absorption of the photocatalytic system to the visible range to certain extent and separate the charge carriers effectively thanks to its conjugated π structure [13,14].
Excess free-electrons activated photocatalytic ability of ZnO films through co-doping of higher oxidation state transition metals Ta and Mo
2020, Inorganic Chemistry CommunicationsCitation Excerpt :The peaks located at 234.6 eV and 237.4 eV correspond to the 3d3/2 and 3d5/2 spin orbits of Mo6+ ions. The energy difference of 2.8 eV confirms the presence of Mo6+ ionic state and substitution in the Zn lattice sites [22]. The high resolution spectra of O1s is shown in Fig. 3(b).
Mechanism of Cs<inf>0.33</inf>Ta<inf>x</inf>W<inf>1-x</inf>O<inf>3</inf> in improving the optical property
2020, Materials Chemistry and Physics