Invention Journal of Research Technology in Engineering & Management (IJRTEM) www.ijrtem.com ǁ Volume 1 ǁ Issue 9 ǁ
ISSN: 2455-3689
Effect of Sn Doping on Structural and Electrical Properties of ZnO Thin Films Prepared by Chemical Spray Pyrolysis Method Sabah. A. Salman*, Salah. Q. Hazza**, Sura. J. Abbas* *Department of Physics, College of Science, University of Diyala, **Department of Physics, College of Education, Al- Mustansiriyah University, Iraq Publication Date: 2 January 2017
Abstract: Un-doped and tin (Sn) doped ZnO films were deposited on heated glass substrates by chemical spray pyrolysis method (CSP). The effect of Sn concentration on the structural, surface morphological and electrical properties of the SnO2 films was investigated. XRD analyses showed that the obtained films are polycrystalline in nature with hexagonal structure with preferred orientation of (101). Doping with tin (Sn) causes increase in the grain size. Atomic force microscopy images showed that the root mean square of the average surface roughness's varied from (1.48 to 3.58) as dopant concentration increased from 0 to 5 wt.%. The electrical properties of the Sn ZnO films were strongly influenced by doping concentration. The electrical resistance of the films was sharply decreased as dopant concentration increased. Keywords: (ZnO) thin films, Sn Doping, Structural and electrical Properties.
INTRODUCTION Transparent conducting 0xide (TCO) thin films have been extensively investigated since they constitute a major stage of the production of electronic devices such as semiconducting and laser emitting devices ]1[. Zince oxide (ZnO) is a direct band gap semiconductor having an energy gap of (3.37 eV) at room temperature with high exciton binding energy of (60 meV), Which make it a good- candidate has potential applications in various fields such as optoelectronic applications ]2[, Liquid crystal displays, heat mirrors and multilayer photo-thermal conversion systems ]3[ ZnO thin films is also used in the fabrication of solar cells ]4[, catalyses ]5[ and gas sensors ]6[. In the form of thin films, ZnO is a very promising alternative in flat display screens ]7[. ZnO thin films have been deposited on different substrates by using different techniques such as RF magnetron sputtering ]8[, spray pyrolysis method ]9[, electro-deposition process ]10[, pulsed laser deposition (PLD) ]11[,sol-gel process ]12[, and molecular beam epitaxy ]13[. Spray pyrolysis, among these methods, is an excellent method for the deposition of thin films of metallic oxides. The doping is achieved by replacing Zn+2 atoms with atoms of elements of higher valance, such as Al +3, In+3, Ga+3, Sn+4,Ge+4,Pb+4 ]14[. In this work, un-doped and Sn-doped (ZnO) films have been prepared by using spray pyrolysis technique. The effects of Sn doping concentration on the electronic transitions of (ZnO) films have been reported.
EXPERIMENTAL PROCEDURE Chemical spray pyrolysis technique was used to deposit undoped and Sn-doped (ZnO) films on glass substrates at temperature of (400 ºC). The spray solution was prepared by mixing of (0.1M) aqueous solution of Zinc acetate ((CH3COO)2.2H2O) and (0.1M) aqueous solution Tin Chloride (SnCl4.5H2O). Other deposition conditions such as spray nozzle substrate distance (30±1 cm), spray time (10s), spray interval (3min) and pressure of the carrier gas (1.5 bar) were kept constant for each of the prepared films, Thickness of the sample was measured using the weighting method and was found to be around (400±20nm). The X-ray diffraction patterns for the prepared films were obtained in a (Shimadzu XRD-6000) using copper target (CuKα, 1.5416 Å) and Atomic Force Microscopy (AFM) micrographs were recorded by using scanning probe microscope type (SPM- AA3000). The sample resistance measured in RT.
RESULTS AND DISCUSSION The X-ray diffraction patterns of undoped and Sn doped (ZnO) deposited at (400°C) are shown in Figure (1). The highest four diffraction peaks are (100), (101), (002) and (103), which is in agreement with the (JCPDS) standard data with a hexagonal unit cell showing a preferred orientation along (101). Sn doping led to increase in the intensity of the diffraction peaks. As shown in Figure(1) no peaks of Sn, SnO2, or SnS were detected, which indicates that incorporation of Sn ions does not affect the crystal structure of ZnO film, This result is in good agreement with literature data [15]. The values of lattice constants a and c are calculated using equation (1) and the calculated values are given in Table[1], it is seen that the calculated values are in good agreement with the standard values for ZnO wurtzite structure[16,17]:
1 4 h 2 hk k 2 l 2 2 d2 3 a2 c
……… (1)
where ‘d’ is the interplanar spacing and h, k, and l are the Miller indices. | Volume 1 | Issue 9 |
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Effect of SN Doping on Structural and Electrical Properties of ZnO Thin Films Prepared by Chemical Spray Pyrolysis..... The average crystallite size for the all films is calculated for (101) direction by Scherrer’s formula by using the relation [18]: D = kλ / βhkl cosӨ
..…………. (2)
Where βhkl is full width of half maximum, D is the average crystallite size, k is constant and was assumed to be equal to 0.9, λ is wavelength for Cu target for XRD instrument, θ is Bragg’s angle for all peaks, It is observed that the crystallite size of ZnO thin films from the (101) peaks increases when ratio of doping by Sn increases as shown in figure(2). Structural parameters of Sn-doped ZnO thin films shown in Table (1).
Figure(1) X-ray diffraction pattern of the undoped and Sn doped ZnO
Figure(2) Average crystallite size as a function of doping percentage Table (1) Structural parameters of Sn-doped zinc oxide thin films
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Sample
ZnO Pure
ZnO:Sn )1%)
ZnO:Sn (3%)
ZnO:Sn (5%)
Dav(nm) Scherrer
19.7
20.5
20.7
21.5
Lattice constant (a) (JCPDS) )3.2498 Å) Lattice Constant (c) )JCPDS) 5.206 Å)
3.2443
3.249
3.2503
3.2513
5.19998
5.20276
5.20442
5.20638
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Effect of SN Doping on Structural and Electrical Properties of ZnO Thin Films Prepared by Chemical Spray Pyrolysis..... The 3D AFM micrographs of the undoped and Sn doped ZnO thin films are shown in Figure (4). The size of the scanned area was (2*2) Îźm2. AFM results show homogenous and smooth thin films. The average roughness and root mean square (RMS) for all samples estimated from AFM are given in Table (2). The electrical resistance of the films decreased with increasing the doping concentration as shown in figure(4). This increase in conductivity is related to the improvement of crystallinity [19], This result is in good agreement with literature[20].
Figure(3) 3D AFM images of undoped and Sn doped ZnO thin films Table2: The average roughness and root mean square (RMS) for undoped and Sn doped thin films.
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Sample
Surface roughness (nm)
RMS (nm)
ZnO
1.28
1.48
ZnO:Sn (1%)
1.58
1.83
ZnO:Sn (3%)
1.88
2.11
ZnO:Sn (5%)
3.07
3.58
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Effect of SN Doping on Structural and Electrical Properties of ZnO Thin Films Prepared by Chemical Spray Pyrolysis.....
Resistance MΊ
2.5 2
1.5
1
0.5 0 0
1
2
3
4
5
6
Sn percentage % Figure(4) Resistance as a function of doping Sn doped ZnO thin films. CONCLUSIONS Transparent oxide semiconductor thin films of zinc oxide and tin-doped zinc oxide have been successfully prepared on to glass substrate by the chemical spray pyrolysis technique. The Influence of doping on structural , morphological and electrical properties of these films was investigated. The XRD results showed that all films are polycrystalline in nature with hexagonal structure and preferred orientation along (101) plane. The intensity of peaks and crystallite size increased with increasing of doping. AFM results showed that the average roughness and root mean square (RMS) increased with increasing of doping, while the resistance decreased with increasing of Sn concentration.
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Effect of SN Doping on Structural and Electrical Properties of ZnO Thin Films Prepared by Chemical Spray Pyrolysis..... [18] [19] [20]
R. H. Bari and S. B. Patil, "Studies on spray pyrolised nanostructured SnO2 thin films for H2 gas sensing application", International Letters of Chemistry, Physics and Astronomy, 17 (2), (2014)pp. (125-141). A. Bougrine, M.Addou, A. Kachouane, J.C.Bernede, M.Mors, "Effect of tin incorporation on physicochemical properties of ZnO films prepared by spray pyrolysis", Materials Chemistry and Physics 91(2–3), (2005), pp. 247–252. S.Aksoy, "Some physical properties of tin doped ZnO thin films", M.S. Thesis, Graduate School of Sciences, Anadolu University, Eskisehir, Turkey, (2006).
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