- Email: [email protected]
Investigation of the optical properties of the indium-doped ZnO thin films deposited by a thermionic vacuum arc
Optik 157 (2018) 667–674
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Investigation of the optical properties of the indium-doped ZnO thin films deposited by a thermionic vacuum arc Reza Mohammadigharehbagh a,b , Suat Pat a,∗ , Soner Özen a , H. Hakan Yudar a , S¸adan Korkmaz a a b
Department of Physics, Eskis¸ehir Osmangazi University, Eskis¸ehir 26480, Turkey Department of Physics, Urmia Branch, Islamic Azad University, Urmia, Iran
a r t i c l e
i n f o
Article history: Received 11 May 2017 Received in revised form 17 November 2017 Accepted 18 November 2017 Keyword: Optical properties TVA Thin film XRD FESEM
a b s t r a c t In this paper, the investigation of optical properties of an indium-doped ZnO (IZO) thin films deposited on glass and polyethylene terephthalate (PET) by thermionic vacuum arc technique were done. Also, the surface, structural and electrical properties of deposited films were studied by an atomic force microscopy (AFM), field emission electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet-visible (UV–vis) spectrophotometer, interferometer and Hall effect system. Using a Filmetrics F20 thin film measurement system, the thickness values of the deposited IZO thin films were obtained as to be 110 nm and 190 nm on glass and PET substrates, respectively. All IZO films are in a polycrystalline structure. The estimated mean crystallite size values were recorded as 29.34 nm and 28.17 nm on the glass and PET substrates, respectively. The surface images of the FESEM analysis show growth of granular structure on the surface and the results are in good agreement with AFM results. Using UV–vis spectrophotometer and interferometer, the refractive index, reflectance, transmittance, absorbance and optical band gap of the deposited films were determined. The calculated optical band gap values of the films are obtained as to 3.64 eV and 3.55 eV for glass and PET substrate, respectively. The electrical measurements show that sheet resistance is dependence on the substrate materials. © 2017 Elsevier GmbH. All rights reserved.
1. Introduction Zinc oxide (ZnO) is an II–VI compounds semiconductors. The crystal structure of ZnO is hexagonal wurtzite structure. The doped ZnO materials are alternative material for the transparent conductive oxide (TCO). Hence, it causes attentions for many researchers. It has a large exciton binding energy about 60 meV and direct wide band gap (Eg ∼3.37 eV) [1]. Doped ZnO materials have been deposited using various methods such as RF sputtering [2], chemical vapor deposition [3], sol–gel [4], laser ablation, spray pyrolysis, reactive evaporation [5], pulsed laser deposition [6], chemical bath [7], chemical spray [8], electrostatic spray deposition [9]. Indium-tin oxide (ITO) is one of reported the most popular TCO materials. Due to the wide band gap, inexpensive, low electrical resistivity, high transparency, chemical stability and low roughness value of the indium doped ZnO thin films, it can be a good alternative instead of the well – known ITO thin films in the technological
∗ Corresponding author. E-mail address: [email protected] (S. Pat). https://doi.org/10.1016/j.ijleo.2017.11.102 0030-4026/© 2017 Elsevier GmbH. All rights reserved.
668
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
Table 1 The effective TVA parameters during the deposition process. Samples
ZnO: In/Glass ZnO: In/PET
Discharge current (A) Deposition time (s) Working pressure (Torr) Applied voltage (V) Filament current (A)
0.4 160 9 × 10−5 200 18
applications [10,11]. ZnO material can doped with a various type of dopants such as carbon, fluorine, gallium, aluminium, tin, iron, nickel, antimony and etc [12–15]. In the present paper, we focus on the investigation of optical properties of indium-doped ZnO thin films deposited on glass and PET substrates by thermionic vacuum arc (TVA) technique for the first time. TVA is a rapid deposition technology for the thin film deposition [16,17]. Atomic force microscope (AFM), field emissions scanning electron microscope, X-ray diffractometer, UV–vis spectrophotometer, Filmetrics F20 thin film thickness measurement system and Hall effect measurement system was used to determine the properties of the deposited samples. 2. Experimental details The fundamental principle of the TVA thin film deposition has been explained in the literature in detail [16,17]. First of all, the substrates were cleaned using the ultrasonic bath to remove presence contamination few times with duration of 15 min. Then substrate and desired amount of IZO were placed inside the sample holder and crucible. TVA is an anodic plasma generator, it works in high vacuum condition. TVA has an anode and cathode electrode. As the anode, an electron gun is used. Firstly, materials temperatures were increased by electron impact under the accelerative DC high voltage. In that time, if DC voltage increased to the higher values, a plasma created in the inter-electrodic space. This is called as thermionic vacuum arc plasma. The distance between anode and substrate holder was adjusted to 80 mm. In addition, the distance between anode and cathode kept constant as 4 mm during the experiment. All working parameters of the TVA technique are tabulated in Table 1. 3. Results and discussion An Ambios Q-Scope atomic force microscope (AFM) was used for the surface characteristics of the deposited IZO films. The measurements were done at non – contact mode and room temperature. Scan Atomic V5.1.0 SPM software was used for the surface characteristics of the deposited samples. The applied scan rate and scan angles were 6 Hz and 0◦ . AFM is a more proper and non-destructive device for determination of the surface properties of the coated materials. All surfaces of the deposited layers were scanned in the range of 4 m × 4 m. The two (2D) and three (3D) dimensions surface images are shown in Fig. 1a–d. For the glass substrate, AFM images are shown in Fig. 1a and c. Fig. 1b and d images are belonging to the PET substrate. These images are very similar to each other. The height distribution graphs are plotted in Fig. 1e. Mean values of these graphs are approximately 180 nm and 350 nm. According to these images, the IZO grains on PET substrate are bigger than the value of the glass substrate. The root – mean – square roughness (RMS) of coated films decrease from 105 nm to 70 nm in the case of PET substrates relative to the glass substrate as well. The skewness (Ssk) and kurtosis (Skr) values of deposited films were measured by Scan Atomic V5.1.0 SPM software. These values are implies the symmetry of the peaks and valleys for the deposited films. If the Ssk equal to zero, it causes to symmetrical normal distribution. The Ssk values of negative and positive point out downward and upward orientation respect to the mean line. The kurtosis (Skr) values, Skr value evaluates of surface sharpness. Ssk values were determined as to be 0.49 and 0.77 for glass and PET substrate, respectively. Also, Skr values were calculated as to be 0.82 and 1.26 for glass and PET substrate, respectively. The Zeiss supra 40VP model was used for the field emission scanning electron microscopy (FESEM) images of the IZO films deposited by TVA technique. Obtained images are shown in Fig. 2a and b. According to the images, the ball – like nanocrystalline structures was grown on the substrates. The crystallite sizes the films deposited onto PET surface are bigger than the values for the glass substrate crystalline sizes. Furthermore, FESEM images have uniformity and lack of crack and void for the deposited films. The images were taken in 50kx magnifications. Panalytical Empryan X-ray diffraction (XRD) device were used for the measurement. XRD patterns and assignments of the reflections of the planes are illustrated in Fig. 3. XRD patterns were recorded in the range of 20◦ –80◦ for 2-theta. It is concluded that deposited films are in polycrystal form. For each XRD pattern, a dominant peak is related with the In2 O3 (222). All indexed peaks are in a good agreement with the values which is reported in the literature [12,18] and JCPDS card no 21-1272. In the XRD pattern, only two main PET peaks determined which are assigned to the at the 53.63◦ and 64.54◦ positions [19]. In2 O3 , In and ZnO reflection planes (JCPDS card no 36-1451) are shown in XRD patterns. Especially, indium reflection (In) planes (JCPDS card no 5-642) are also seen in clearly in XRD patterns for the deposited IZO thin film onto PET substrate. It was concluded that substrate materials are play an important role for the microstructural properties of the deposited layers because of the crystalline nature of the PET substrate materials.
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
669
Fig. 1. 2D and 3D images of coated IZO thin films on a, c) glass and b, d) PET substrates and e) height distribution graphs.
Poly-crystalline thin films on amorphous substrates can be deposited by RF magnetron sputtering, plasma chemical vapor deposition, pulsed laser deposition and etc [20–24]. At relatively low temperatures, poly-crystal films cannot deposit on glass substrate. For the higher temperatures or higher plasma energy (in plasma assisted thin film deposition process), poly-crystal films can deposit. Ion energy in plasma or plasma assistant deposition process is an important for the film microstructure properties. The ion energy in TVA deposition is greater than the RF sputter and plasma assistant deposition technology. The ion energy in TVA can adjust up to 500 eV [16]. Classical deposition process in RF sputters has reach to a few ten eV for ion energy. By the means of the higher ion energy, poly-crystalline thin films can be deposit on glass substrate, directly. Using the Filmetrics F20 tool, the thicknesses values of the IZO films were measured as 110 nm and 190 nm for glass and PET, respectively. The presence of In2 O3 phase within the IZO films structure is indicative of the flaw and defect in the
670
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
Fig. 2. FESEM images of IZO thin films deposited on a) glass and b) PET substrates.
Fig. 3. The XRD patterns of the prepared IZO films on the glass and PET substrates.
crystallisation process. For calculation of mean crystallite size of films, the Debye-Scherrer equation is employed [25]. This relation is shown in Eq. (1). k  cos
D=
(1)
Where, k, and  are defined as the shape factor (equal to 1), X-ray wavelength (0.15406 nm) and expansion in the full – width at half maximum (FWHM), respectively. Moreover, is the Bragg diffraction angle. The highest mean crystallite size values evaluated are 29.34 nm and 28.17 nm for glass and PET samples that proved the coating of the surface by nano – particles. The dislocation density (␦) and microstrain () of the prepared thin films evaluated according to the Williamson and Smallman formula ı=
1 D2
(2)
ε=
ˇ cos 4
(3)
and
The lattice strain of the films, ∈ calculated given by the following equation, ∈=
ˇ 4 tan
(4)
which, D is mean crystallite size of the samples and obtained from Eq. (1). In addition, the number of crystallite per unit area (N) also computed for deposited samples respect to the formula explained as: N=
t D3
(5)
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
671
Table 2 The calculated important XRD parameters of the coated IZO thin films on glass and PET substrates. Peak degree (◦ )
Diffraction plane
Phase
Mean Crystallite size (nm)
Dislocation density (␦) (m−2 ) × 1015
Micro -strain () × 10−3
Lattice strain ×10−3
N. C (m−2 ) × 1015
Glass substrate
29.06 33.05 35.67 39.24 42.92 47.33 48.27 57.30
222 101 101 111 332 102 211 110
I2 O3 Indium ZnO Indium In2 O3 ZnO In2 O3 ZnO
22.46 22.39 29.34 22.51 22.63 19.16 22.04 19.09
1.98 1.99 1.16 1.97 1.95 2.72 2.06 2.74
1.57 1.58 1.20 1.57 1.56 1.84 1.60 1.85
6.30 5.60 3.90 4.70 4.30 4.60 3.90 3.90
9.70 9.80 4.35 9.65 9.49 15.6 10.3 15.8
PET substrate
22.44 29.27 31.37 32.84 35.78 39.24 43.02 47.43 48.48 50.89 53.63 54.36 56.46 57.30 60.66 63.18 64.55 65.59 66.96 69.17 70.22 72.95
211 222 100 101 101 111 332 102 211 440 – 112 200 110 622 103 – 444 211 202 201 004
In2 O3 In2 O3 ZnO Indium ZnO Indium In2 O3 ZnO In2 O3 In2 O3 PET Indium Indium ZnO In2 O3 Indium PET In2 O3 Indium Indium ZnO ZnO
10.34 23.70 12.41 24.52 18.14 19.58 22.37 22.56 22.35 27.38 – 22.82 27.19 22.24 22.61 19.22 – 28.17 28.12 19.05 22.63 19.12
9.36 1.78 6.49 1.66 3.04 2.61 2.00 1.96 2.00 1.33 – 1.92 1.35 2.02 1.95 2.71 – 1.26 1.26 2.75 1.95 2.73
3.42 1.49 2.85 1.44 1.95 1.80 1.58 1.57 1.58 1.29 – 1.55 1.30 1.59 1.56 1.84 – 1.25 1.26 1.86 1.56 1.85
0.176 5.90 0.105 5.10 6.30 5.40 4.30 3.90 3.90 3.00 – 3.40 2.70 3.30 3.10 3.50 – 2.30 2.30 3.30 2.70 3.10
172 14.3 99.5 12.9 31.8 25.3 17.0 16.5 17.0 92.5 – 16.0 9.45 17.3 16.4 26.7 – 8.50 8.54 27.5 16.4 27.2
where, t is the thickness of the IZO samples deposited on a substrate. There is a direct relation between estimated microstrain results and mean crystallite size values of films. The obtained microstrain of the films gives rise from dislocations, point flaws such as site disorder, vacancies and other imperfections, which exist within the crystal structure. These values also attributed to the growth condition. The calculated data from the XRD results are shown in Table 2. Optical properties of the deposited IZO films on glass and PET substrates were investigated in the wavelength between 300 and 1000 nm. The absorbance and transmittance graphs were obtained via the UV–vis spectrophotometer (UNICO 4802 double beam). Obtained absorbance and transmittance graphs are shown in Fig. 4a and b, respectively. The reflectance and refractive index of deposited films were obtained via Filmetrics F20 interferometer. These graphs are illustrated in Fig. 4c and d. From the spectra, the mean values of absorbance and transmittance for IZO samples recorded as 0.59 and 63% on a glass substrate as well as 1.31 and 38% on PET substrate, respectively. The obtained refractive index, n values for all samples have consistent with other research present in the literature [26]. It was pointed that refractive index (n) values for all samples decrease by increasing the wavelength, but reduction shape should be carried out in a different way. The optical band gap of deposited IZO films estimated using the well – known Tauc formula [27,28]:
˛h = A h − Eg
n
(6)
where, A, h and ␣ are constant, incident photon energy and optical absorption coefficient of the films, respectively. In addition, Eg represented as optical band gap of the IZO films in the Tauc formula. Indeed, n in the Eq. (6) shows the electronic transitions of materials. The symbol can get four different values (1/2, 2, 3/2 or 3) and related with the direct and indirect allowed as well as direct and indirect forbidden transitions. For our deposited samples, n is equal to ½, which indicates the direct allowed transition because; the straight lines for the band gap calculations are the best in obtained graphs in Fig. 5. For calculation of the optical absorption coefficient, ␣ of the samples, the below equation employed: ˛=
1 1 ln ⁄T d
(7)
where, d and T are the thickness and transmittance value for the deposited samples.The band gap values have been determined by plotting the (␣h)2 in terms of photon energy of the thin films. Obtained band gap graphs are seen in Fig. 5. The intercept of the described red line with h axis was defined the band gap values of the prepared thin films. It is evident that these value obtained as to be 3.20 eV and 3.205 eV for glass and PET substrates, respectively. These obtained results show very good harmony with the related papers [29,30].
672
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
Fig. 4. a) Absorbance, b) transmittance, c) refractive index and d) reflectance of the prepared IZO films.
Fig. 5. The calculated band gap of the IZO thin films on glass and PET substrates.
The electrical characteristics of deposited IZO thin films were determined using a Hall effect measurement (HMS 3000 apparatus) system in order to four – probe van der Pauw technique. All tests were done in the room temperature for whole samples. Before starting the measurement, Ag paste was applied to the four corners of the films. Using a Hall effect measurement system, the sheet resistance (Rs ), resistivity, mobility (), and conductivity () of the prepared films were obtained. The average sheet resistance, Rs of the films were obtained as to be 2.2 × 102 cm2 and 8.2 × 102 cm2 on glass and PET substrates, respectively. For the calculation of the sheet resistance, R = R s Lt/A
(8)
where, L is the length, A is the cross section area and t is the thickness of the deposited layer. The average mobility of the IZO samples obtained as 4.9 × 10−1 cm2 /Vs and 9.7 × 10−2 cm2 /Vs on glass and PET substrates in the measured range, respectively. The measured resistivity of In-doped ZnO films was specified of 4.4 × 10−3 cm and 8.2 × 10−5 cm. The obtained resistivity values are very close to literature values [31,32]. In this case, the conductivity () of the films was determined as 2.2 × 102 cm−1 and 1.2 × 104 cm−1 on glass and PET substrates, respectively. The obtained values for electrical characteristics of the IZO films on different substrates were listed in Table 3. The obtained conductivity and resistivity values have been implied homogeneity and smoothness of the particles without any disorder in the lattice. Also, the values were
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
673
Table 3 The obtained electrical parameters of the deposited IZO thin films on glass and PET substrates. Samples
Glass substrate
Test Current
Carrier Concentration (cm−3 ) × 1022
Mobility (cm2 /V s) × 10−1
Sheet resistance (/square) × 102
Resistivity ( cm) × 10−4
Conductivity (1/ cm) × 103
145 A 150 A 160 A 170 A 180 A 190 A 200 A
0.232 0.936 0.229 0.119 0.177 0.652 0.257 0.492 0.412 163.5 150.3 597.1 291.9 158.3 872.7 905.9 586.3
5.98 1.48 6.05 11.8 7.86 2.15 5.46 4.957 3.502 0.4648 0.5054 0.1273 0.2603 0.4805 0.8715 0.9701 0.7769
2.256 2.255 2.253 2.228 2.250 2.228 2.227 2.245 0.01295 8.216 8.216 8.212 8.213 8.209 8.207 8.211 0.4298
45.18 45.15 45.10 44.62 45.07 44.61 44.59 44.95 0. 2592 0.8216 0.8216 0.8212 0.8213 0.8209 0.8207 0.8211 0.0004298
0.2214 0.2215 0.2217 0.2241 0.2219 0.2241 0.2243 0.2225 0.001287 12.17 12.17 12.18 12.18 12.18 12.18 12.18 0.0006901
Average value Standard Deviation
PET substrate
100 A 110 A 120 A 130 A 140 A 150 A
Average value Standard Deviation
pointed out the lack of segregation of indium at grain boundaries of the prepared films, which paved the way of electron transport mechanism [33–35]. 4. Conclusion Thermionic vacuum arc (TVA) technology is a rapid technology, which produced samples contain low precursor and process impurity according to other physical and chemical vapor deposition technology. So, as a different technology, In doped ZnO thin films has been deposited by TVA. Deposited technology affects the all properties of the deposited films. Thus, In-doped ZnO films were deposited by TVA technology in this research activity. Some of the physical properties of prepared films carried out. In addition, this paper has been reported the potential features of the growth technique for fabrication of smooth, dense, polycrystalline and uniform thin films. XRD patterns indicate that deposited films were formed in the polycrystalline structure. The band gap of the deposited films was calculated as to 3.64 eV and 3.55 eV for glass and PET substrate, respectively. The average sheet resistance values were calculated as to be 2.2 × 102 and 8.2 × 102 ohm/square for deposited on glass and PET substrate, respectively. Carrier concentrations were measured as to be 4.9 × 1021 and 9.0 × 1023 for deposited on glass and PET substrate, respectively. Acknowledgement This research activity was supported by Eskisehir Osmangazi University Scientific Research council (Grant number is: 201619053). References [1] V.K. Jayaraman, Y.M. Kuwabara, A.M. Álvarez, Importance of substrate rotation speed on the growth of homogeneous ZnO thin films by reactive sputtering, Mater. Lett. 169 (2016) 1–4. [2] V. S¸enay, S. Pat, S¸. Korkmaz, T. Aydo˘gmus¸, S. Elmas, S. Özen, N. Ekem, M.Z. Balba˘g, ZnO thin film synthesis by reactive radio frequency magnetron sputtering, Appl. Surf. Sci. 318 (2014) 2–5. [3] M. Nolan, J. Hamilton, S. O’Brien, G. Bruno, L. Pereira, E. Fortunato, R. Martins, I. Povey, M. Pemble, The characterisation of aerosol assisted CVD conducting, photocatalytic indium doped zinc oxide films, J. Photochem. Photobiol. A: Chem. 219 (2011) 10–15. [4] Y. Li, L. Xu, X. Li, X. Shen, A. Wang, Effect of aging time of ZnO sol on the structural and optical properties of ZnO thin films prepared by sol–gel method, Appl. Surf. Sci. 256 (2010) 4543–4547. [5] X.-j. Wang, Q.-s. Lei, W. Xu, W.-l. Zhou, J. Yu, Preparation of ZnO: Al thin film on transparent TPT substrate at room temperature by RF magnetron sputtering technique, Mater. Lett. 63 (2009) 1371–1373. [6] O. Jayakumar, A. Tyagi, Effect of oxygen pressure on room-temperature ferromagnetism of Al co-doped Mn doped ZnO thin films prepared by pulsed laser deposition, Int. J. Nanotechnol. 7 (2010) 1047–1053. [7] E. Pál, V. Hornok, A. Oszkó, I. Dékány, Hydrothermal synthesis of prism-like and flower-like ZnO and indium-doped ZnO structures, Colloids Surf. A 340 (2009) 1–9. [8] Q. Xiu-Juan, H. Si-Hui-Zhi, Z. Lin, Z. Hua-Tong, S. Shi-Tao, Fabrication of transparent conductive Al-doped ZnO thin films by aerosol-assisted chemical vapour deposition, J. Inorg. Mater. 26 (2011) 607–612. [9] D.H. Chi, N.T. Binh, N.N. Long, Band-edge photoluminescence in nanocrystalline ZnO: In films prepared by electrostatic spray deposition, Appl. Surf. Sci. 252 (2006) 2770–2775. [10] S. Benramache, B. Benhaoua, H. Bentrah, Preparation of transparent, conductive ZnO: Co and ZnO: In thin films by ultrasonic spray method, J. Nanostruct. Chem. 3 (2013) 54. [11] M. Caglar, S. Ilican, Y. Caglar, Influence of dopant concentration on the optical properties of ZnO: in films by sol–gel method, Thin Solid Films 517 (2009) 5023–5028. [12] R. Mohammadigharehbagh, S. Özen, H.H. Yudar, V. S¸enay, S. Pat, S¸. Korkmaz, Investigation on the physical properties of C-doped ZnO thin films deposited by the thermionic vacuum arc, Eur. Phys. J. Plus 132 (2017) 28.
674
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
[13] S. Fabbiyola, V. Sailaja, L.J. Kennedy, M. Bououdina, J.J. Vijaya, Optical and magnetic properties of Ni-doped ZnO nanoparticles, J. Alloys Compd. 694 (2017) 522–531. [14] P. Ariyakkani, L. Suganya, B. Sundaresan, Investigation of the structural, optical and magnetic properties of Fe doped ZnO thin films coated on glass by sol-gel spin coating method, J. Alloys Compd. 695 (2017) 3467–3475. [15] R. Nasser, W.B.H. Othmen, H. Elhouichet, M. Férid, Preparation, characterization of Sb-doped ZnO nanocrystals and their excellent solar light driven photocatalytic activity, Appl. Surf. Sci. 393 (2017) 486–495. [16] S. Pat, N. Ekem, T. Akan, O. Kusmus, S. Demirkol, R. Vladoiu, C.P. Lungu, G. Musa, Study on thermionic vacuum arc–a novel and advanced technology for surface coating, J. Optoelectron. Adv. Mater. 7 (5) (2005) 2495–2499. [17] S. Pat, M.Z. Balba˘g, S¸. Korkmaz, Mechanical properties of deposited carbon thin films on sapphire substrates using atomic force microscopy (AFM), Ceram. Int. 40 (7) (2014) 10159–10162. [18] L. Qin, P. Dutta, S. Sawyer, Photoresponse of indium oxide particulate-based thin films fabricated using milled nanorods grown by the self-catalytic vapor–liquid–solid process, Semicond. Sci. Technol. 27 (2012) 045005. [19] S. Pat, S. Özen, V. S¸enay, S¸. Korkmaz, Comparisons of surface and optical properties of the heavily carbon-doped GaN nanocrystalline films deposited by thermionic vacuum arc method, Vacuum 133 (2016) 38–42. [20] C.H. Wei, C.M. Chang, Polycrystalline TiO2 thin films with different thicknesses deposited on unheated substrates using RF magnetron sputtering, Mater. Trans. 52 (3) (2011) 554–559. [21] K.L. Ekinci, J.M. Valles, Formation of polycrystalline structure in metallic films in the early stages of Zone I growth, Acta Mater. 46 (13) (1998) 4549–4557. [22] J.I. Woo, H.J. Lim, J. Jang, Polycrystalline silicon thin film transistors deposited at low substrate temperature by remote plasma chemical vapor deposition using SiF4/H2, Appl. Phys. Lett. 65 (13) (1994) 1644–1646. [23] A. Taabouche, A. Bouabellou, F. Kermiche, F. Hanini, S. Menakh, Y. Bouachiba, T. Kerdja, C. Benazzouz, M. Bouafia, S. Amara, Effect of substrates on the properties of ZnO thin films grown by pulsed laser deposition, Adv. Mater. Phys. Chem. 3 (04) (2013) 209–213. [24] T. Pisarkiewicz, H. Jankowski, E. Schabowska-Osiowska, L.J. Maksymowicz, Fabrication of thin film polycrystalline CIS photovoltaic heterostructure, Optoelectron. Rev. (4) (2003) 297–304. [25] B. Cullity, Structure of polycrystalline aggregates Elements of X-ray Diffraction, vol. 2, Addison-Wesley, 2017. [26] G. Xie, L. Fanga, L. Peng, G. Liu, H. Ruan, F. Wu, C. Kong, Effect of In-doping on the optical constants of ZnO thin films, Phys. Procedia 32 (2012) 651–657. [27] J. Tauc, R. Grigorovici, A. Vancu, Optical properties and electronic structure of amorphous germanium, Physica Status Solidi (b) 15 (1966) 627–637. [28] S¸. Korkmaz, B. Gec¸ici, S.D. Korkmaz, R. Mohammadigharehbagh, S. Pat, S. Özen, V. S¸enay, H.H. Yudar, Morphology, composition, structure and optical properties of CuO/Cu 2 O thin films prepared by RF sputtering method, Vacuum 131 (2016) 142–146. [29] S. Benramache, O. Belahssen, H.B. Temam, Effect of band gap energy on the electrical conductivity in doped ZnO thin film, J. Semicond. 35 (2014) 073001. [30] R. Biswal, A. Maldonado, J. Vega-Pérez, D.R. Acosta, M. De La Luz Olvera, Indium doped zinc oxide thin films deposited by ultrasonic chemical spray technique, starting from zinc acetylacetonate and indium chloride, Materials 7 (2014) 5038–5046. [31] V. Craciun, C. Martin, G. Socol, D. Tanner, H. Swart, N. Becherescu, D. Craciun, Optical properties of amorphous indium zinc oxide thin films synthesized by pulsed laser deposition, Appl. Surf. Sci. 306 (2014) 52–55. [32] Y.S. Rim, S.M. Kim, K.H. Kim, Properties of indium-zinc-oxide thin films prepared by facing targets sputtering at room temperature, J. Korean Phys. Soc. 54 (2009) 1267–1272. [33] P. Nunes, F.M. Braz Fernandes, R.J.C. Silva, E. Fortunato, R. Martins, Structural characterisation of zinc oxide thin films produced by spray pyrolysis, in: Key Engineering Materials, Trans Tech Publ, 2002, pp. 599–602. [34] B. Joseph, P. Manoj, V. Vaidyan, Studies on preparation and characterization of indium doped zinc oxide films by chemical spray deposition, Bull. Mater. Sci. 28 (2005) 487–493. [35] Y. Caglar, M. Zor, M. Caglar, S. Ilican, Influence of the indium incorporation on the structural and electrical properties of zinc oxide films, J. Optoelectron. Adv. Mater. 8 (2006) 1867–1873.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Investigation of the optical properties of the indium-doped ZnO thin films deposited by a thermionic vacuum arc Reza Mohammadigharehbagh a,b , Suat Pat a,∗ , Soner Özen a , H. Hakan Yudar a , S¸adan Korkmaz a a b
Department of Physics, Eskis¸ehir Osmangazi University, Eskis¸ehir 26480, Turkey Department of Physics, Urmia Branch, Islamic Azad University, Urmia, Iran
a r t i c l e
i n f o
Article history: Received 11 May 2017 Received in revised form 17 November 2017 Accepted 18 November 2017 Keyword: Optical properties TVA Thin film XRD FESEM
a b s t r a c t In this paper, the investigation of optical properties of an indium-doped ZnO (IZO) thin films deposited on glass and polyethylene terephthalate (PET) by thermionic vacuum arc technique were done. Also, the surface, structural and electrical properties of deposited films were studied by an atomic force microscopy (AFM), field emission electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet-visible (UV–vis) spectrophotometer, interferometer and Hall effect system. Using a Filmetrics F20 thin film measurement system, the thickness values of the deposited IZO thin films were obtained as to be 110 nm and 190 nm on glass and PET substrates, respectively. All IZO films are in a polycrystalline structure. The estimated mean crystallite size values were recorded as 29.34 nm and 28.17 nm on the glass and PET substrates, respectively. The surface images of the FESEM analysis show growth of granular structure on the surface and the results are in good agreement with AFM results. Using UV–vis spectrophotometer and interferometer, the refractive index, reflectance, transmittance, absorbance and optical band gap of the deposited films were determined. The calculated optical band gap values of the films are obtained as to 3.64 eV and 3.55 eV for glass and PET substrate, respectively. The electrical measurements show that sheet resistance is dependence on the substrate materials. © 2017 Elsevier GmbH. All rights reserved.
1. Introduction Zinc oxide (ZnO) is an II–VI compounds semiconductors. The crystal structure of ZnO is hexagonal wurtzite structure. The doped ZnO materials are alternative material for the transparent conductive oxide (TCO). Hence, it causes attentions for many researchers. It has a large exciton binding energy about 60 meV and direct wide band gap (Eg ∼3.37 eV) [1]. Doped ZnO materials have been deposited using various methods such as RF sputtering [2], chemical vapor deposition [3], sol–gel [4], laser ablation, spray pyrolysis, reactive evaporation [5], pulsed laser deposition [6], chemical bath [7], chemical spray [8], electrostatic spray deposition [9]. Indium-tin oxide (ITO) is one of reported the most popular TCO materials. Due to the wide band gap, inexpensive, low electrical resistivity, high transparency, chemical stability and low roughness value of the indium doped ZnO thin films, it can be a good alternative instead of the well – known ITO thin films in the technological
∗ Corresponding author. E-mail address: [email protected] (S. Pat). https://doi.org/10.1016/j.ijleo.2017.11.102 0030-4026/© 2017 Elsevier GmbH. All rights reserved.
668
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
Table 1 The effective TVA parameters during the deposition process. Samples
ZnO: In/Glass ZnO: In/PET
Discharge current (A) Deposition time (s) Working pressure (Torr) Applied voltage (V) Filament current (A)
0.4 160 9 × 10−5 200 18
applications [10,11]. ZnO material can doped with a various type of dopants such as carbon, fluorine, gallium, aluminium, tin, iron, nickel, antimony and etc [12–15]. In the present paper, we focus on the investigation of optical properties of indium-doped ZnO thin films deposited on glass and PET substrates by thermionic vacuum arc (TVA) technique for the first time. TVA is a rapid deposition technology for the thin film deposition [16,17]. Atomic force microscope (AFM), field emissions scanning electron microscope, X-ray diffractometer, UV–vis spectrophotometer, Filmetrics F20 thin film thickness measurement system and Hall effect measurement system was used to determine the properties of the deposited samples. 2. Experimental details The fundamental principle of the TVA thin film deposition has been explained in the literature in detail [16,17]. First of all, the substrates were cleaned using the ultrasonic bath to remove presence contamination few times with duration of 15 min. Then substrate and desired amount of IZO were placed inside the sample holder and crucible. TVA is an anodic plasma generator, it works in high vacuum condition. TVA has an anode and cathode electrode. As the anode, an electron gun is used. Firstly, materials temperatures were increased by electron impact under the accelerative DC high voltage. In that time, if DC voltage increased to the higher values, a plasma created in the inter-electrodic space. This is called as thermionic vacuum arc plasma. The distance between anode and substrate holder was adjusted to 80 mm. In addition, the distance between anode and cathode kept constant as 4 mm during the experiment. All working parameters of the TVA technique are tabulated in Table 1. 3. Results and discussion An Ambios Q-Scope atomic force microscope (AFM) was used for the surface characteristics of the deposited IZO films. The measurements were done at non – contact mode and room temperature. Scan Atomic V5.1.0 SPM software was used for the surface characteristics of the deposited samples. The applied scan rate and scan angles were 6 Hz and 0◦ . AFM is a more proper and non-destructive device for determination of the surface properties of the coated materials. All surfaces of the deposited layers were scanned in the range of 4 m × 4 m. The two (2D) and three (3D) dimensions surface images are shown in Fig. 1a–d. For the glass substrate, AFM images are shown in Fig. 1a and c. Fig. 1b and d images are belonging to the PET substrate. These images are very similar to each other. The height distribution graphs are plotted in Fig. 1e. Mean values of these graphs are approximately 180 nm and 350 nm. According to these images, the IZO grains on PET substrate are bigger than the value of the glass substrate. The root – mean – square roughness (RMS) of coated films decrease from 105 nm to 70 nm in the case of PET substrates relative to the glass substrate as well. The skewness (Ssk) and kurtosis (Skr) values of deposited films were measured by Scan Atomic V5.1.0 SPM software. These values are implies the symmetry of the peaks and valleys for the deposited films. If the Ssk equal to zero, it causes to symmetrical normal distribution. The Ssk values of negative and positive point out downward and upward orientation respect to the mean line. The kurtosis (Skr) values, Skr value evaluates of surface sharpness. Ssk values were determined as to be 0.49 and 0.77 for glass and PET substrate, respectively. Also, Skr values were calculated as to be 0.82 and 1.26 for glass and PET substrate, respectively. The Zeiss supra 40VP model was used for the field emission scanning electron microscopy (FESEM) images of the IZO films deposited by TVA technique. Obtained images are shown in Fig. 2a and b. According to the images, the ball – like nanocrystalline structures was grown on the substrates. The crystallite sizes the films deposited onto PET surface are bigger than the values for the glass substrate crystalline sizes. Furthermore, FESEM images have uniformity and lack of crack and void for the deposited films. The images were taken in 50kx magnifications. Panalytical Empryan X-ray diffraction (XRD) device were used for the measurement. XRD patterns and assignments of the reflections of the planes are illustrated in Fig. 3. XRD patterns were recorded in the range of 20◦ –80◦ for 2-theta. It is concluded that deposited films are in polycrystal form. For each XRD pattern, a dominant peak is related with the In2 O3 (222). All indexed peaks are in a good agreement with the values which is reported in the literature [12,18] and JCPDS card no 21-1272. In the XRD pattern, only two main PET peaks determined which are assigned to the at the 53.63◦ and 64.54◦ positions [19]. In2 O3 , In and ZnO reflection planes (JCPDS card no 36-1451) are shown in XRD patterns. Especially, indium reflection (In) planes (JCPDS card no 5-642) are also seen in clearly in XRD patterns for the deposited IZO thin film onto PET substrate. It was concluded that substrate materials are play an important role for the microstructural properties of the deposited layers because of the crystalline nature of the PET substrate materials.
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
669
Fig. 1. 2D and 3D images of coated IZO thin films on a, c) glass and b, d) PET substrates and e) height distribution graphs.
Poly-crystalline thin films on amorphous substrates can be deposited by RF magnetron sputtering, plasma chemical vapor deposition, pulsed laser deposition and etc [20–24]. At relatively low temperatures, poly-crystal films cannot deposit on glass substrate. For the higher temperatures or higher plasma energy (in plasma assisted thin film deposition process), poly-crystal films can deposit. Ion energy in plasma or plasma assistant deposition process is an important for the film microstructure properties. The ion energy in TVA deposition is greater than the RF sputter and plasma assistant deposition technology. The ion energy in TVA can adjust up to 500 eV [16]. Classical deposition process in RF sputters has reach to a few ten eV for ion energy. By the means of the higher ion energy, poly-crystalline thin films can be deposit on glass substrate, directly. Using the Filmetrics F20 tool, the thicknesses values of the IZO films were measured as 110 nm and 190 nm for glass and PET, respectively. The presence of In2 O3 phase within the IZO films structure is indicative of the flaw and defect in the
670
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
Fig. 2. FESEM images of IZO thin films deposited on a) glass and b) PET substrates.
Fig. 3. The XRD patterns of the prepared IZO films on the glass and PET substrates.
crystallisation process. For calculation of mean crystallite size of films, the Debye-Scherrer equation is employed [25]. This relation is shown in Eq. (1). k  cos
D=
(1)
Where, k, and  are defined as the shape factor (equal to 1), X-ray wavelength (0.15406 nm) and expansion in the full – width at half maximum (FWHM), respectively. Moreover, is the Bragg diffraction angle. The highest mean crystallite size values evaluated are 29.34 nm and 28.17 nm for glass and PET samples that proved the coating of the surface by nano – particles. The dislocation density (␦) and microstrain () of the prepared thin films evaluated according to the Williamson and Smallman formula ı=
1 D2
(2)
ε=
ˇ cos 4
(3)
and
The lattice strain of the films, ∈ calculated given by the following equation, ∈=
ˇ 4 tan
(4)
which, D is mean crystallite size of the samples and obtained from Eq. (1). In addition, the number of crystallite per unit area (N) also computed for deposited samples respect to the formula explained as: N=
t D3
(5)
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
671
Table 2 The calculated important XRD parameters of the coated IZO thin films on glass and PET substrates. Peak degree (◦ )
Diffraction plane
Phase
Mean Crystallite size (nm)
Dislocation density (␦) (m−2 ) × 1015
Micro -strain () × 10−3
Lattice strain ×10−3
N. C (m−2 ) × 1015
Glass substrate
29.06 33.05 35.67 39.24 42.92 47.33 48.27 57.30
222 101 101 111 332 102 211 110
I2 O3 Indium ZnO Indium In2 O3 ZnO In2 O3 ZnO
22.46 22.39 29.34 22.51 22.63 19.16 22.04 19.09
1.98 1.99 1.16 1.97 1.95 2.72 2.06 2.74
1.57 1.58 1.20 1.57 1.56 1.84 1.60 1.85
6.30 5.60 3.90 4.70 4.30 4.60 3.90 3.90
9.70 9.80 4.35 9.65 9.49 15.6 10.3 15.8
PET substrate
22.44 29.27 31.37 32.84 35.78 39.24 43.02 47.43 48.48 50.89 53.63 54.36 56.46 57.30 60.66 63.18 64.55 65.59 66.96 69.17 70.22 72.95
211 222 100 101 101 111 332 102 211 440 – 112 200 110 622 103 – 444 211 202 201 004
In2 O3 In2 O3 ZnO Indium ZnO Indium In2 O3 ZnO In2 O3 In2 O3 PET Indium Indium ZnO In2 O3 Indium PET In2 O3 Indium Indium ZnO ZnO
10.34 23.70 12.41 24.52 18.14 19.58 22.37 22.56 22.35 27.38 – 22.82 27.19 22.24 22.61 19.22 – 28.17 28.12 19.05 22.63 19.12
9.36 1.78 6.49 1.66 3.04 2.61 2.00 1.96 2.00 1.33 – 1.92 1.35 2.02 1.95 2.71 – 1.26 1.26 2.75 1.95 2.73
3.42 1.49 2.85 1.44 1.95 1.80 1.58 1.57 1.58 1.29 – 1.55 1.30 1.59 1.56 1.84 – 1.25 1.26 1.86 1.56 1.85
0.176 5.90 0.105 5.10 6.30 5.40 4.30 3.90 3.90 3.00 – 3.40 2.70 3.30 3.10 3.50 – 2.30 2.30 3.30 2.70 3.10
172 14.3 99.5 12.9 31.8 25.3 17.0 16.5 17.0 92.5 – 16.0 9.45 17.3 16.4 26.7 – 8.50 8.54 27.5 16.4 27.2
where, t is the thickness of the IZO samples deposited on a substrate. There is a direct relation between estimated microstrain results and mean crystallite size values of films. The obtained microstrain of the films gives rise from dislocations, point flaws such as site disorder, vacancies and other imperfections, which exist within the crystal structure. These values also attributed to the growth condition. The calculated data from the XRD results are shown in Table 2. Optical properties of the deposited IZO films on glass and PET substrates were investigated in the wavelength between 300 and 1000 nm. The absorbance and transmittance graphs were obtained via the UV–vis spectrophotometer (UNICO 4802 double beam). Obtained absorbance and transmittance graphs are shown in Fig. 4a and b, respectively. The reflectance and refractive index of deposited films were obtained via Filmetrics F20 interferometer. These graphs are illustrated in Fig. 4c and d. From the spectra, the mean values of absorbance and transmittance for IZO samples recorded as 0.59 and 63% on a glass substrate as well as 1.31 and 38% on PET substrate, respectively. The obtained refractive index, n values for all samples have consistent with other research present in the literature [26]. It was pointed that refractive index (n) values for all samples decrease by increasing the wavelength, but reduction shape should be carried out in a different way. The optical band gap of deposited IZO films estimated using the well – known Tauc formula [27,28]:
˛h = A h − Eg
n
(6)
where, A, h and ␣ are constant, incident photon energy and optical absorption coefficient of the films, respectively. In addition, Eg represented as optical band gap of the IZO films in the Tauc formula. Indeed, n in the Eq. (6) shows the electronic transitions of materials. The symbol can get four different values (1/2, 2, 3/2 or 3) and related with the direct and indirect allowed as well as direct and indirect forbidden transitions. For our deposited samples, n is equal to ½, which indicates the direct allowed transition because; the straight lines for the band gap calculations are the best in obtained graphs in Fig. 5. For calculation of the optical absorption coefficient, ␣ of the samples, the below equation employed: ˛=
1 1 ln ⁄T d
(7)
where, d and T are the thickness and transmittance value for the deposited samples.The band gap values have been determined by plotting the (␣h)2 in terms of photon energy of the thin films. Obtained band gap graphs are seen in Fig. 5. The intercept of the described red line with h axis was defined the band gap values of the prepared thin films. It is evident that these value obtained as to be 3.20 eV and 3.205 eV for glass and PET substrates, respectively. These obtained results show very good harmony with the related papers [29,30].
672
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
Fig. 4. a) Absorbance, b) transmittance, c) refractive index and d) reflectance of the prepared IZO films.
Fig. 5. The calculated band gap of the IZO thin films on glass and PET substrates.
The electrical characteristics of deposited IZO thin films were determined using a Hall effect measurement (HMS 3000 apparatus) system in order to four – probe van der Pauw technique. All tests were done in the room temperature for whole samples. Before starting the measurement, Ag paste was applied to the four corners of the films. Using a Hall effect measurement system, the sheet resistance (Rs ), resistivity, mobility (), and conductivity () of the prepared films were obtained. The average sheet resistance, Rs of the films were obtained as to be 2.2 × 102 cm2 and 8.2 × 102 cm2 on glass and PET substrates, respectively. For the calculation of the sheet resistance, R = R s Lt/A
(8)
where, L is the length, A is the cross section area and t is the thickness of the deposited layer. The average mobility of the IZO samples obtained as 4.9 × 10−1 cm2 /Vs and 9.7 × 10−2 cm2 /Vs on glass and PET substrates in the measured range, respectively. The measured resistivity of In-doped ZnO films was specified of 4.4 × 10−3 cm and 8.2 × 10−5 cm. The obtained resistivity values are very close to literature values [31,32]. In this case, the conductivity () of the films was determined as 2.2 × 102 cm−1 and 1.2 × 104 cm−1 on glass and PET substrates, respectively. The obtained values for electrical characteristics of the IZO films on different substrates were listed in Table 3. The obtained conductivity and resistivity values have been implied homogeneity and smoothness of the particles without any disorder in the lattice. Also, the values were
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
673
Table 3 The obtained electrical parameters of the deposited IZO thin films on glass and PET substrates. Samples
Glass substrate
Test Current
Carrier Concentration (cm−3 ) × 1022
Mobility (cm2 /V s) × 10−1
Sheet resistance (/square) × 102
Resistivity ( cm) × 10−4
Conductivity (1/ cm) × 103
145 A 150 A 160 A 170 A 180 A 190 A 200 A
0.232 0.936 0.229 0.119 0.177 0.652 0.257 0.492 0.412 163.5 150.3 597.1 291.9 158.3 872.7 905.9 586.3
5.98 1.48 6.05 11.8 7.86 2.15 5.46 4.957 3.502 0.4648 0.5054 0.1273 0.2603 0.4805 0.8715 0.9701 0.7769
2.256 2.255 2.253 2.228 2.250 2.228 2.227 2.245 0.01295 8.216 8.216 8.212 8.213 8.209 8.207 8.211 0.4298
45.18 45.15 45.10 44.62 45.07 44.61 44.59 44.95 0. 2592 0.8216 0.8216 0.8212 0.8213 0.8209 0.8207 0.8211 0.0004298
0.2214 0.2215 0.2217 0.2241 0.2219 0.2241 0.2243 0.2225 0.001287 12.17 12.17 12.18 12.18 12.18 12.18 12.18 0.0006901
Average value Standard Deviation
PET substrate
100 A 110 A 120 A 130 A 140 A 150 A
Average value Standard Deviation
pointed out the lack of segregation of indium at grain boundaries of the prepared films, which paved the way of electron transport mechanism [33–35]. 4. Conclusion Thermionic vacuum arc (TVA) technology is a rapid technology, which produced samples contain low precursor and process impurity according to other physical and chemical vapor deposition technology. So, as a different technology, In doped ZnO thin films has been deposited by TVA. Deposited technology affects the all properties of the deposited films. Thus, In-doped ZnO films were deposited by TVA technology in this research activity. Some of the physical properties of prepared films carried out. In addition, this paper has been reported the potential features of the growth technique for fabrication of smooth, dense, polycrystalline and uniform thin films. XRD patterns indicate that deposited films were formed in the polycrystalline structure. The band gap of the deposited films was calculated as to 3.64 eV and 3.55 eV for glass and PET substrate, respectively. The average sheet resistance values were calculated as to be 2.2 × 102 and 8.2 × 102 ohm/square for deposited on glass and PET substrate, respectively. Carrier concentrations were measured as to be 4.9 × 1021 and 9.0 × 1023 for deposited on glass and PET substrate, respectively. Acknowledgement This research activity was supported by Eskisehir Osmangazi University Scientific Research council (Grant number is: 201619053). References [1] V.K. Jayaraman, Y.M. Kuwabara, A.M. Álvarez, Importance of substrate rotation speed on the growth of homogeneous ZnO thin films by reactive sputtering, Mater. Lett. 169 (2016) 1–4. [2] V. S¸enay, S. Pat, S¸. Korkmaz, T. Aydo˘gmus¸, S. Elmas, S. Özen, N. Ekem, M.Z. Balba˘g, ZnO thin film synthesis by reactive radio frequency magnetron sputtering, Appl. Surf. Sci. 318 (2014) 2–5. [3] M. Nolan, J. Hamilton, S. O’Brien, G. Bruno, L. Pereira, E. Fortunato, R. Martins, I. Povey, M. Pemble, The characterisation of aerosol assisted CVD conducting, photocatalytic indium doped zinc oxide films, J. Photochem. Photobiol. A: Chem. 219 (2011) 10–15. [4] Y. Li, L. Xu, X. Li, X. Shen, A. Wang, Effect of aging time of ZnO sol on the structural and optical properties of ZnO thin films prepared by sol–gel method, Appl. Surf. Sci. 256 (2010) 4543–4547. [5] X.-j. Wang, Q.-s. Lei, W. Xu, W.-l. Zhou, J. Yu, Preparation of ZnO: Al thin film on transparent TPT substrate at room temperature by RF magnetron sputtering technique, Mater. Lett. 63 (2009) 1371–1373. [6] O. Jayakumar, A. Tyagi, Effect of oxygen pressure on room-temperature ferromagnetism of Al co-doped Mn doped ZnO thin films prepared by pulsed laser deposition, Int. J. Nanotechnol. 7 (2010) 1047–1053. [7] E. Pál, V. Hornok, A. Oszkó, I. Dékány, Hydrothermal synthesis of prism-like and flower-like ZnO and indium-doped ZnO structures, Colloids Surf. A 340 (2009) 1–9. [8] Q. Xiu-Juan, H. Si-Hui-Zhi, Z. Lin, Z. Hua-Tong, S. Shi-Tao, Fabrication of transparent conductive Al-doped ZnO thin films by aerosol-assisted chemical vapour deposition, J. Inorg. Mater. 26 (2011) 607–612. [9] D.H. Chi, N.T. Binh, N.N. Long, Band-edge photoluminescence in nanocrystalline ZnO: In films prepared by electrostatic spray deposition, Appl. Surf. Sci. 252 (2006) 2770–2775. [10] S. Benramache, B. Benhaoua, H. Bentrah, Preparation of transparent, conductive ZnO: Co and ZnO: In thin films by ultrasonic spray method, J. Nanostruct. Chem. 3 (2013) 54. [11] M. Caglar, S. Ilican, Y. Caglar, Influence of dopant concentration on the optical properties of ZnO: in films by sol–gel method, Thin Solid Films 517 (2009) 5023–5028. [12] R. Mohammadigharehbagh, S. Özen, H.H. Yudar, V. S¸enay, S. Pat, S¸. Korkmaz, Investigation on the physical properties of C-doped ZnO thin films deposited by the thermionic vacuum arc, Eur. Phys. J. Plus 132 (2017) 28.
674
R. Mohammadigharehbagh et al. / Optik 157 (2018) 667–674
[13] S. Fabbiyola, V. Sailaja, L.J. Kennedy, M. Bououdina, J.J. Vijaya, Optical and magnetic properties of Ni-doped ZnO nanoparticles, J. Alloys Compd. 694 (2017) 522–531. [14] P. Ariyakkani, L. Suganya, B. Sundaresan, Investigation of the structural, optical and magnetic properties of Fe doped ZnO thin films coated on glass by sol-gel spin coating method, J. Alloys Compd. 695 (2017) 3467–3475. [15] R. Nasser, W.B.H. Othmen, H. Elhouichet, M. Férid, Preparation, characterization of Sb-doped ZnO nanocrystals and their excellent solar light driven photocatalytic activity, Appl. Surf. Sci. 393 (2017) 486–495. [16] S. Pat, N. Ekem, T. Akan, O. Kusmus, S. Demirkol, R. Vladoiu, C.P. Lungu, G. Musa, Study on thermionic vacuum arc–a novel and advanced technology for surface coating, J. Optoelectron. Adv. Mater. 7 (5) (2005) 2495–2499. [17] S. Pat, M.Z. Balba˘g, S¸. Korkmaz, Mechanical properties of deposited carbon thin films on sapphire substrates using atomic force microscopy (AFM), Ceram. Int. 40 (7) (2014) 10159–10162. [18] L. Qin, P. Dutta, S. Sawyer, Photoresponse of indium oxide particulate-based thin films fabricated using milled nanorods grown by the self-catalytic vapor–liquid–solid process, Semicond. Sci. Technol. 27 (2012) 045005. [19] S. Pat, S. Özen, V. S¸enay, S¸. Korkmaz, Comparisons of surface and optical properties of the heavily carbon-doped GaN nanocrystalline films deposited by thermionic vacuum arc method, Vacuum 133 (2016) 38–42. [20] C.H. Wei, C.M. Chang, Polycrystalline TiO2 thin films with different thicknesses deposited on unheated substrates using RF magnetron sputtering, Mater. Trans. 52 (3) (2011) 554–559. [21] K.L. Ekinci, J.M. Valles, Formation of polycrystalline structure in metallic films in the early stages of Zone I growth, Acta Mater. 46 (13) (1998) 4549–4557. [22] J.I. Woo, H.J. Lim, J. Jang, Polycrystalline silicon thin film transistors deposited at low substrate temperature by remote plasma chemical vapor deposition using SiF4/H2, Appl. Phys. Lett. 65 (13) (1994) 1644–1646. [23] A. Taabouche, A. Bouabellou, F. Kermiche, F. Hanini, S. Menakh, Y. Bouachiba, T. Kerdja, C. Benazzouz, M. Bouafia, S. Amara, Effect of substrates on the properties of ZnO thin films grown by pulsed laser deposition, Adv. Mater. Phys. Chem. 3 (04) (2013) 209–213. [24] T. Pisarkiewicz, H. Jankowski, E. Schabowska-Osiowska, L.J. Maksymowicz, Fabrication of thin film polycrystalline CIS photovoltaic heterostructure, Optoelectron. Rev. (4) (2003) 297–304. [25] B. Cullity, Structure of polycrystalline aggregates Elements of X-ray Diffraction, vol. 2, Addison-Wesley, 2017. [26] G. Xie, L. Fanga, L. Peng, G. Liu, H. Ruan, F. Wu, C. Kong, Effect of In-doping on the optical constants of ZnO thin films, Phys. Procedia 32 (2012) 651–657. [27] J. Tauc, R. Grigorovici, A. Vancu, Optical properties and electronic structure of amorphous germanium, Physica Status Solidi (b) 15 (1966) 627–637. [28] S¸. Korkmaz, B. Gec¸ici, S.D. Korkmaz, R. Mohammadigharehbagh, S. Pat, S. Özen, V. S¸enay, H.H. Yudar, Morphology, composition, structure and optical properties of CuO/Cu 2 O thin films prepared by RF sputtering method, Vacuum 131 (2016) 142–146. [29] S. Benramache, O. Belahssen, H.B. Temam, Effect of band gap energy on the electrical conductivity in doped ZnO thin film, J. Semicond. 35 (2014) 073001. [30] R. Biswal, A. Maldonado, J. Vega-Pérez, D.R. Acosta, M. De La Luz Olvera, Indium doped zinc oxide thin films deposited by ultrasonic chemical spray technique, starting from zinc acetylacetonate and indium chloride, Materials 7 (2014) 5038–5046. [31] V. Craciun, C. Martin, G. Socol, D. Tanner, H. Swart, N. Becherescu, D. Craciun, Optical properties of amorphous indium zinc oxide thin films synthesized by pulsed laser deposition, Appl. Surf. Sci. 306 (2014) 52–55. [32] Y.S. Rim, S.M. Kim, K.H. Kim, Properties of indium-zinc-oxide thin films prepared by facing targets sputtering at room temperature, J. Korean Phys. Soc. 54 (2009) 1267–1272. [33] P. Nunes, F.M. Braz Fernandes, R.J.C. Silva, E. Fortunato, R. Martins, Structural characterisation of zinc oxide thin films produced by spray pyrolysis, in: Key Engineering Materials, Trans Tech Publ, 2002, pp. 599–602. [34] B. Joseph, P. Manoj, V. Vaidyan, Studies on preparation and characterization of indium doped zinc oxide films by chemical spray deposition, Bull. Mater. Sci. 28 (2005) 487–493. [35] Y. Caglar, M. Zor, M. Caglar, S. Ilican, Influence of the indium incorporation on the structural and electrical properties of zinc oxide films, J. Optoelectron. Adv. Mater. 8 (2006) 1867–1873.