Analysis of the electrical impedance spectroscopy measurements of ZnTe:Ni thin film deposited by R–F sputtering

Journal Pre-proof Analysis of the electrical impedance spectroscopy measurements of ZnTe:Ni thin film deposited by R-F sputtering

M. Chaik, S. Ben Moumen, R. Bouferra, A.Outzourhit, L. Essaleh PII:

S0749-6036(19)31150-4

DOI:

https://doi.org/10.1016/j.spmi.2019.106319

Reference:

YSPMI 106319

To appear in:

Superlattices and Microstructures

Received Date:

01 July 2019

Accepted Date:

23 October 2019

Please cite this article as: M. Chaik, S. Ben Moumen, R. Bouferra, A.Outzourhit, L. Essaleh, Analysis of the electrical impedance spectroscopy measurements of ZnTe:Ni thin film deposited by R-F sputtering, Superlattices and Microstructures (2019), https://doi.org/10.1016/j.spmi. 2019.106319

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Journal Pre-proof Analysis of the electrical impedance spectroscopy measurements of ZnTe:Ni thin film deposited by R-F sputtering

M. Chaik1, S. Ben Moumen2, R. Bouferra2, A.Outzourhit1, L. Essaleh2

1Laboratory

of Nanomaterials, Energy and Environment (LNEE), Faculty of Sciences Semlalia, Cadi Ayyad University, PO Box: 2390, Marrakech 40000, Morocco 2Laboratory

of Condensed Matter and Nanostructures (LMCN), Cadi-Ayyad University, Faculty of Sciences and Technology, Marrakech, Morocco.

Abstract

In the present work, ZnTe:Ni thin films were prepared using the R-F sputtering technique. X-ray diffractogramme indicates that our samples are crystallized in a cubic phase with a F-43m space group. The UV visible spectrophotometer confirms the good quality of the deposited films and also the similitude of the value of the optical band gap energy with those reported in the literature. Electrical impedance spectroscopy data were analyzed to estimate the activation and relaxation energies. In the considered temperature (303 - 483 K) and frequency (20 Hz – 1 MHz) ranges, we show that both “grain” and “grain boundary” contributions govern the AC electrical conductivity. The data are discussed in the light of existing theoretical models.

Keywords: Semiconductor Compounds; Electrical Conductivity; Thin Films.

*

Corresponding author: M. Chaik

Phone: (+212) 658369094 , E-mail: [email protected]

Journal Pre-proof Introduction: In the last few decades, a large number of researches were developed in the goal to find IIVI semiconductor materials with a large band gap [1–3]. One of the most known materials exhibiting this behavior is the Zinc Telluride (ZnTe) semiconductor [4]. This latter was used in the field of radiation [5], photo-detectors [6], terahertz (THz) devices [7] and especially in the solar cells applications [8,9] presenting a direct band gap of 2.26 eV at room temperature [10,11]. In the goal to modify their properties, it is familiar that the doping has attractive results on semiconductor materials. Cu, Cd, and Cr doped ZnTe materials [5,12,13] were extensively studied and show good enhancement of their optical [14], optoelectrical [15] and dielectric [16] properties. At the best of our knowledge, no study on the impedance spectroscopy (IS) properties was reported for Ni doped. (IS) is known to be a reliable technique for the electrical characterization of disordered semiconducting materials by measuring their response while applying an AC signal [17]. This technique permits the determination of the internal structure of the material through the separation between the different existing contributions [18]. This asset is widely used in recent years on the bulk materials [19–21] . In this study, Ni doped ZnTe thin films were prepared using the R-F Sputtering method, the AC electrical conductivity in the temperature [303 - 483 K] and frequency [20 Hz, 1 MHz] ranges were investigated. An adequate electrical equivalent circuit is considered to fit the experimental data. 1. Experimental details Thin Nickel doped Zinc Telluride films were deposited on glass substrates by using a reactive RF magnetron sputtering (Alcatel SCM 451 system operating at 13.56 MHz) and a pure Zinc Telluride (ZnTe) target with 10 cm diameter. The doping process was guaranteed by covering the ZnTe target by a piece of pure Nickel. The covered surface was estimated to be about 0.44%. Before placing them in the chamber, the substrates were pre-cleaned by ethanol and then with acetone under ultrasonic waves for 20 min, after that, they have been rinsed with distilled water and then dried by hot air. The deposition was carried out under argon (Ar) plasma for a fixed time of 1 hour. The sputtering chamber was initially cleaned and prompted to a base pressure (Pb) of ∼2x10-6 mbar. The device is equipped with a regulator managing the introduction and the control of reactive sputtering gases in the chamber. The sputtering pressure (Ps) and RF power (Pw) were preserved at 50 W and 10-2 mbar, respectively during all the process. Before the deposition on the samples, a pre-

Journal Pre-proof sputtering of the target was carried out in Ar at room temperature for ∼15 min so as to remove any susceptible existing oxide layer. The optical gap energy Eg and optical properties of the deposited thin-films were calculated using the transmittance plot versus wavelength measured via the UV-VIS-NIR spectrophotometer (Shimadzu UV-PC spectrophotometer) in the 200–3000 nm wavelength range. The structural properties of the deposited samples were carried out by X-ray diffraction using a (RIGAKU Smart lab SE diffractometer) and the AC electrical measurements were done by an HP 4284A system in a frequency range from 20 Hz to 1 MHz. 2. Experimental results and discussion 2.1 Optical and structural properties In order to investigate the optical properties of the fabricated ZnTe:Ni thin films, the UVVisible-NIR spectrophotometry analysis was performed. Fig.1 represents the transmittance versus the wavelength and the results shows the presence of clear interference fringes evidencing the high quality and the smoothness of the thin films surfaces. Furthermore a good transmittance in the infrared and the visible ranges is achieved by the deposited samples allowing their use in many applications. Otherwise, the band gap was estimated by using Tauc method based on the following equation [23]: α. hν = A (hν − Eg)1/2

(1)

where A is a constant and α is the absorption coefficient. The extrapolation of the linear part of the (α·hν)2 as a function of incident photon energy hν curve gives us the optical band gap Eg. This latter was obtained from the intercept between the extrapolated curve and the X axis while (α·hν)2=0. Comparing with the literature where the band gap of the intrinsic ZnTe is equal 2.26 eV [10,24], in our ZnTe:Ni samples we notice a small increase of this value achieving 2.30 eV. The observed increase could be due to the Moss-Burstein effect [25,26]. The thickness of the film is calculated using the Swanepoel method [27] and it found to be 566 nm. The ZnTe:Ni thin film X-ray diffraction pattern is presented in Fig. 2. It is clear that no impurities were detected in the diffractogramme even with the introduction of Nickel. All the characteristic peaks of ZnTe phase are identified and the asterisk marked ones refers to the Alumina sample carrier of the X-ray apparatus. Confirming that Nickel has not affected the

Journal Pre-proof structural properties of the thin film. These remarks indicate that our sample crystallizes in the cubic structure with a F-43m space group according to the JCPDS (01-0582) card. A high peak intensity is observed at 2=25.41° position, indicating a preferential orientation along the (111) plane in the sample. The calculated value of the cell parameter a using the Bragg’s formula is found to be 6.027 Å and it is approximately close to the value reported for ZnTe [28]. Then the average crystallite size was given using Debye Scherrer’s formula [29]: λ k

(2)

D = β cosθ

where, k is equal to 0.9,  is the X-ray wavelength,  is the diffraction peak angle and β is the full-linewidth at half maximum of the (111) peak. The extracted value of D is equal to 2.72 nm. 2.2 AC electrical properties The complex impedance (Z*) formalism is usually used to identify the contribution of largest resistance. According to the classical theory of Debye [30], Z* is given by: 𝑅

𝑍 ∗ = 𝑍' +𝑗𝑍", where 𝑍' = 1 + (𝜔𝜏)2 and 𝑍" = ― 𝑅

(

𝜔𝜏

)

1 + (𝜔𝜏)2

(3)

where R and C represent the resistance and the capacitance of the material. By using these expressions of Eqn. (3) and by plotting both 𝑍' and 𝑍" versus frequency, we can see that a minimum of 𝑍" corresponds to an inflexion point in 𝑍'. The relaxation time  satisfies the condition 2𝜋𝑓0𝜏 = 1 where fo is the frequency at which the curve 𝑍" versus frequency presents a minimum. This is shown in Fig. 3a where 𝑍' and 𝑍" are plotted as function of frequency for several representatives values of temperature from 303 to 483 K. Two contributions are well identified: one in the low frequency and the other in the high frequency ranges. For example at T = 303 K the peaks are located at 462 Hz and 105 kHz while at T = 483 K, the corresponding frequencies are 1.88 kHz and 363 kHz. This indicates the displacement of the peaks towards high frequencies when increasing temperature. In addition to Z*, the electric modulus (M*) formalism can also be used in order to identify the contribution of smallest capacitance, namely the “grain” contribution. M* is given by [30]

Journal Pre-proof 𝑀 ∗ = 𝑗𝜔𝐶𝑜𝑍 ∗ = 𝑀' +𝑗𝑀'' , where 𝑀' =

(

𝐶𝑜

(𝜔𝜏)2

) and 𝑀 = ( "

𝐶 1 + (𝜔𝜏)2

𝐶𝑜

𝜔𝜏

)

𝐶 1 + (𝜔𝜏)2

(4)

where Co is the capacitance of the empty cell. By using the expressions of Eqn. (3) and Eqn. (4) and by plotting both 𝑍" and M” versus frequency, we can see that a minimum of 𝑍"corresponds to maximum in M”. This is shown in Fig. 3b where 𝑍" and 𝑀'' are plotted against frequency for several representatives values of temperature. The coincidence of the minima in 𝑍" with the maxima in M” in the high frequency range indicates that this peak is associated to the “grain” contribution in which the capacitance is very small ranging between 10-12 - 10-11 F. It follows then that the observed minima in 𝑍" in the low frequency range represents the “grain boundary” contribution where the capacitance is so high achieving values in the range of 10-10 - 10-9 F. The variation of AC electrical conductivity versus frequency for different values of temperature is given in Fig. 4. Two dispersion regions appear also in these spectra that can be associated to the low frequency dispersion and another at higher frequencies. The high frequency domain is related to the grain (HF-G) while the low frequency dispersion is associated to the grain boundary (LF-GB). Usually the AC conductivity is interpreted by using the Jonscher equation [31]: 𝜎 = 𝜎(𝜔,𝑇) = 𝐴(𝑇) 𝜔𝑠(𝜔,𝑇)

(5)

In order to analyze the observed two contributions, we represent in Fig. 5(a and b) the Nyquist diagram (variation of 𝑍" versus Z’ ) for several representative temperatures from 300K to 483K. In general, the presence of three semicircles in the Nyquist plots is commonly attributed to three contributions: grain, grain boundary, electrodes at high, intermediate and low frequency respectively. For our present material, the presence of the two semicircles as seen in Fig.5(a and b) indicates two contributions which are identified by comparing their capacitance using an electrical equivalent circuit consisting of two parallel elements RCPE connected in series[(RLF// CPELF) + (RHF// CPEHF)]. The impedance of the constant phase element CPEi is given by 𝑍𝐶𝑃𝐸𝑖 =

1 𝑛𝑖

𝑄𝑖(𝑗𝜔)

[32]. From the best fits, also shown in Fig. 5 by

continuous curves, the values of the adjustable parameters Ri, Qi and ni where the index “i” refers to “LF” (Low frequency) and “HF” (High frequency) ranges for the two contributions are determined and presented in Table 1.

Journal Pre-proof As we can see from this table, the capacitance is of the order of 10-11 F for the contribution located in the high frequency region while those of the contribution located in the low frequency region in the order of 10-9 F. Thus, these two contributions are related to the “grain” and “grain-boundary” ones. Their relaxation times and resistance are plotted against the inverse of temperature (1/T) in Fig. 6 and Fig. 7, respectively. The corresponding activation energies for the conduction mechanism (Econd) and for the relaxation (Erelax) process are indicated in these figures. Both, lies in the range 120 - 200 meV. 3. Conclusion AC electrical conduction of ZnTe:Ni thin films deposited by R-F sputtering was investigated by using impedance spectroscopy technique. The two contributions of “grain” and “grain boundary” are clearly identified in the temperature range 303 - 483 K. An adequate electrical equivalent circuit of two blocks of (R//CPE) mounted in series is used to fit and interpret the complex impedance plots. The activation energies for the conduction and for the relaxation processes are determined.

Journal Pre-proof References [1] M. Chaik, S. Ben Moumen, A. Agdad, C.M. SambaVall, H. El Aakib, H. AitDads, A. Outzourhit, L. Essaleh, Electrical impedance spectroscopy characterization of ZnTe thin film deposited by R-F sputtering, Physica B: Condensed Matter. 572 (2019) 76–80. doi:10.1016/j.physb.2019.07.050. [2] A. Ramos-Ruiz, C. Zeng, R. Sierra-Alvarez, L.H. Teixeira, J.A. Field, Microbial toxicity of ionic species leached from the II-VI semiconductor materials, cadmium telluride (CdTe) and cadmium selenide (CdSe), Chemosphere. 162 (2016) 131–138. doi:10.1016/j.chemosphere.2016.07.081. [3] T. Rajesh Kumar, P. Prabukanthan, G. Harichandran, J. Theerthagiri, S. Chandrasekaran, J. Madhavan, Optical, magnetic, and photoelectrochemical properties of electrochemically deposited Eu3+-doped ZnSe thin films, Ionics. 23 (2017) 2497–2507. doi:10.1007/s11581-017-2090-1. [4] Y. Wang, T. He, ZnTe-based nanocatalysts for CO2 reduction, Current Opinion in Green and Sustainable Chemistry. 16 (2019) 7–12. doi:10.1016/j.cogsc.2018.11.005. [5] K. Qin, H. Ji, J. Huang, K. Tang, Y. Shen, X. Zhang, M. Cao, J. Zhang, Y. Shen, L. Wang, The effects of Cu-doped ZnTe intermediate layer on the Ohmic contact to CdZnTe films, Surface and Coatings Technology. 320 (2017) 366–370. doi:10.1016/j.surfcoat.2016.12.027. [6] G.K. Rao, A.V. K., P. K, P. Kumar, Effect of bismuth nanoparticle incorporation on the characteristics of p-ZnTe/n-CdS thin film light sensors, Sensors and Actuators A: Physical. 284 (2018) 194–200. doi:10.1016/j.sna.2018.10.030. [7] N.V. Kinev, K.I. Rudakov, A.M. Baryshev, V.P. Koshelets, Slot Lens Antenna Based on Thin Nb Films for the Wideband Josephson Terahertz Oscillator, Phys. Solid State. 60 (2018) 2173–2177. doi:10.1134/S1063783418110112. [8] A. Luque, A. Martí, C. Stanley, Understanding intermediate-band solar cells, Nature Photon. 6 (2012) 146–152. doi:10.1038/nphoton.2012.1. [9] K. Yoshino, M. Yoneta, K. Ohmori, H. Saito, M. Ohishi, T. Yabe, Annealing effects of a high-quality ZnTe substrate, Journal of Elec Materi. 33 (2004) 579–582. doi:10.1007/s11664-004-0049-2. [10] H. Bellakhder, F. Debbagh, A. Outzourhit, A. Bennouna, M. Brunel, E.L. Ameziane, Characterization of Te/Zn/Te … multilayers deposited by RF-sputtering, Solar Energy Materials and Solar Cells. 45 (1997) 361–368. doi:10.1016/S0927-0248(96)00083-9. [11] Q. Huda, M.M. Aliyu, M.A. Islam, M.S. Hossain, M.M. Alam, M.R. Karim, M.A.M. Bhuiyan, K. Sopian, N. Amin, CdZnTe thin films growth by RF sputtering for CdTe solar cells, in: 2013 IEEE 39th Photovoltaic Specialists Conference (PVSC), IEEE, Tampa, FL, USA, 2013: pp. 3480–3483. doi:10.1109/PVSC.2013.6744242. [12] F. Goumrhar, L. Bahmad, O. Mounkachi, A. Benyoussef, Ab-initio calculations for the electronic and magnetic properties of Cr doped ZnTe, Computational Condensed Matter. 15 (2018) 15–20. doi:10.1016/j.cocom.2018.03.003. [13] M.A. Baghchesara, R. Yousefi, M. Cheraghizade, F. Jamali-Sheini, A. Sa’aedi, Photocurrent application of Cd-doped ZnTe nanowires grown in a large scale by a CVD method, Vacuum. 123 (2016) 131–135. doi:10.1016/j.vacuum.2015.10.026. [14] M.A. Kamran, Novel low-temperature synthesis and optical properties of 1D-ZnTe nanowires, Journal of Science: Advanced Materials and Devices. 3 (2018) 226–229. doi:10.1016/j.jsamd.2018.04.001. [15] D. Wu, T. Xu, Z. Shi, Y. Tian, X. Li, Construction of ZnTe nanowires/Si p–n heterojunctions for electronic and optoelectronic applications, Journal of Alloys and Compounds. 661 (2016) 231–236. doi:10.1016/j.jallcom.2015.11.164.

Journal Pre-proof [16] Y. Asadi, Z. Nourbakhsh, First principle study of the structural, electronic, vibrational, thermodynamic, linear and nonlinear optical properties of zinc-blende ZnSe and ZnTe semiconductors, Computational Condensed Matter. 19 (2019) e00372. doi:10.1016/j.cocom.2019.e00372. [17] T. Potlog, Impedance spectroscopy of ZnSe/ZnTe/CdTe thin film heterojunctions, in: CAS 2012 (International Semiconductor Conference), IEEE, Sinaia, Romania, 2012: pp. 261–264. doi:10.1109/SMICND.2012.6400790. [18] Y.Y. Proskuryakov, K. Durose, M.K. Al Turkestani, I. Mora-Seró, G. Garcia-Belmonte, F. Fabregat-Santiago, J. Bisquert, V. Barrioz, D. Lamb, S.J.C. Irvine, E.W. Jones, Impedance spectroscopy of thin-film CdTe/CdS solar cells under varied illumination, Journal of Applied Physics. 106 (2009) 044507. doi:10.1063/1.3204484. [19] S. Amhil, E. choukri, S. Ben Moumen, A. Bourial, L. Essaleh, Evidence of large hopping polaron conduction process in strontium doped calcium copper titanate ceramics, Physica B: Condensed Matter. 556 (2019) 36–41. doi:10.1016/j.physb.2018.12.032. [20] S. Ben Moumen, A. Neqali, B. Asbani, D. Mezzane, M. Amjoud, E.Choukri, Y. Gagou, M. El Marssi, I.A. Luk’yanchuk, Impedance spectroscopy studies on lead free Ba 1-x Mg x (Ti 0.9 Zr 0.1 )O 3 ceramics, Superlattices and Microstructures. 118 (2018) 45–54. doi:10.1016/j.spmi.2018.04.012. [21] S. Amhil, L. Essaleh, S.M. Wasim, G. Marín, E. Choukri, Low temperature analysis of the electrical conduction with the NSPT mechanism in p -CuIn 3 Se 5, Superlattices and Microstructures. 119 (2018) 194–200. doi:10.1016/j.spmi.2018.04.051. [22] S. Ben Moumen, A. Neqali, B. Asbani, D. Mezzane, M. Amjoud, E.Choukri, Y. Gagou, M. El Marssi, I.A. Luk’yanchuk, Impedance spectroscopy studies on lead free Ba 1-x Mg x (Ti 0.9 Zr 0.1 )O 3 ceramics, Superlattices and Microstructures. 118 (2018) 45–54. doi:10.1016/j.spmi.2018.04.012. [23] G.K. Rao, A.V. K., P. K, P. Kumar, Effect of bismuth nanoparticle incorporation on the characteristics of p-ZnTe/n-CdS thin film light sensors, Sensors and Actuators A: Physical. 284 (2018) 194–200. doi:10.1016/j.sna.2018.10.030. [24] O. Skhouni, A. El Manouni, M. Mollar, R. Schrebler, B. Marí, ZnTe thin films grown by electrodeposition technique on Fluorine Tin Oxide substrates, Thin Solid Films. 564 (2014) 195–200. doi:10.1016/j.tsf.2014.06.002. [25] S.N. Svitasheva, A.M. Gilinsky, Influence of doping level on shift of the absorption edge of gallium nitride films (Burstein-Moss effect), Applied Surface Science. 281 (2013) 109–112. doi:10.1016/j.apsusc.2013.02.094. [26] R. Anuroop, B. Pradeep, Effects of Sn doping on the optoelectronic properties of reactively evaporated In4Se3 thin films, Materials Science in Semiconductor Processing. 98 (2019) 19–28. doi:10.1016/j.mssp.2019.03.020. [27] D. Dorranian, L. Dejam, G. Mosayebian, Optical characterization of Cu3N thin film with Swanepoel method, J Theor Appl Phys. 6 (2012) 13. doi:10.1186/2251-7235-6-13. [28] Collaboration: Authors and editors of the volumes III/17B-22A-41B, Zinc telluride (ZnTe) crystal structure, lattice parameters, thermal expansion, in: O. Madelung, U. Rössler, M. Schulz (Eds.), II-VI and I-VII Compounds; Semimagnetic Compounds, Springer-Verlag, Berlin/Heidelberg, 1999: pp. 1–8. doi:10.1007/10681719_494. [29] T. Ivanova, A. Harizanova, T. Koutzarova, B. Vertruyen, Optical characterization of sol–gel ZnO:Al thin films, Superlattices and Microstructures. 85 (2015) 101–111. doi:10.1016/j.spmi.2015.05.013. [30] Macdonald JR, Barsoukov E. Impedance spectroscopy: theory, experiment, and applications. 2nd ed. New York: Wiley-Interscience; 2005., n.d.

Journal Pre-proof [31] A.K. Jonscher, Dielectric Relaxation in Solids, Chelsea Dielectrics Press, London, 1983., n.d. [32] S.R. Elliott, A.c. conduction in amorphous chalcogenide and pnictide semiconductors, Advances in Physics. 36 (1987) 135–217. doi:10.1080/00018738700101971.

100

80

60 (alpha hu)²(ZnTe:Ni(1P) 1h) Linear Fit of REEEEF (alpha hu)²(ZnTe:Ni(1P) 1h)

-2

h eV cm )

2

40

Eg= 2.30 eV



Transmittance (%)

ZnTe:Ni(1P) 1h

20

1.0

0

1.5

2.0

2.5

3.0

Photon energy (eV)

400

800

1200

1600

2000

2400

wavelenght (nm) Fig. 1. Optical transmittance spectra of Nickel doped zinc telluride thin films at rf power 50W, the inset represents the plot of (αhν)2 versus photon energy (hν) of the same sample.

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3000

ZnTe:Ni

(111)

*

2800

(220)

(022)

(400)

(002)

Intensity(a.u.)

2600 2400 2200

*

2000 1800 1600 1400 20

30

40

50

60

70

80

2 

Fig. 2. X-ray diffraction diffractogramme of the Nickel doped zinc telluride thin films.

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0.00

5

-1.50x10

4

-3.00x10

Z " ( )

Z' ()

Z" ()

Z' ()

0.0

5

5.00x10

5

1.59x10

4

7.0x10

4

1.06x10

4

-7.0x10 5

2.50x10

5

-1.4x10

40 °C 1

10

393 K

5

-2.1x10 2

10

3

10

4

5

10

0.00

10

4

1

6

10

10

2

3

10

4

10

10

5

10

6

-4.50x10

10

Frequency (Hz)

Frequency (Hz)

0.00 4

5.20x10

Z" ()

Z' ()

0.00

4

5.30x10

4

3.90x10

3

-8.50x10

4

2.60x10

260 °C 4

1

10

2

10

3

10

4

10

5

10

6

-1.70x10

10

Frequency (Hz)

Fig. 3a. Variation of Z’ and Z’’ as a function of frequency for some representative temperatures (303, 393 and 483 K).

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0.00

4

10

1.26x10

4

-7.0x10

9

6.40x10

Z " ( )

M" ()

0.0

M"

10

1.28x10

Z" ()

7.0x10

40 °C

4

-1.50x10

393 K

9

6.30x10

4

-3.00x10

5

-1.4x10

0.00

0.00 5

-2.1x10 1

10

2

10

3

10

4

5

10

4

1

6

10

10

10

2

3

10

4

10

10

5

10

6

-4.50x10

10

Frequency (Hz)

Frequency (Hz)

0.00 10

M"

Z" ()

1.26x10

3

260 °C

9

6.30x10

-8.50x10

0.00 4

1

10

2

10

3

10

4

10

5

10

6

-1.70x10

10

Frequency (Hz)

Fig. 3b. Variation of Z” and M’’ as a function of frequency for some representative temperatures (303, 393 and 483 K).

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483 K 467 451 435 418 403

-5

Conductivity (S/m)

2.0x10

386 370 354 337 321 303

0.0 3

10

4

10

5

10

6

10

7

10

Frequency (Hz) Fig. 4. Variation of AC electrical conductivity as a function of frequency for several temperatures.

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Fig. 5a. Experimental and calculated Variation of Z’’ as a function of Z’ for some representative temperatures from 303 to 337 K.

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4

1x10

Z'' ()

483 K

451 K 435 K

418 K

403 K

0 4

-1x10

4

-2x10

4

-3x10

Calculated curves 4

-4x10

0.0

4

5

5.0x10

1.0x10

5

1.5x10

Z' () Fig. 5b. Experimental and calculated Variation of Z’’ as a function of Z’ for some representative temperatures from 403 to 483 K.

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-8

-8 Erelax, BF = (203  6)meV -9

-10 Ln (tau_HF)

Ln (tau_BF)

-9

-11 -10

-12 -13

Erelax, HF = (152  3)meV

Linear Fit

-11

-14 -15 -16

-12 -3

2.0x10

-3

-3

2.5x10

3.0x10

-3

3.5x10

-1

1 / T (K )

Fig. 6. Variation of the relaxation time as a function of 1/T for the two observed contributions.

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18.0

Ln(R_HF)

Econd, BF = (198 3)meV

16.2

12 Econd, HF = (152 2)meV

11

10

9 -3 2.0x10

12.6

Linear Fit

-3

-3

2.5x10

14.4

3.0x10

-3

3.5x10

-1

1 / T (K )

Fig. 7. Variation of the resistance as a function of 1/T for the two observed contributions.

Ln(R_BF)

13

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Table 1 : Values of the equivalent circuit parameters calculated at different temperatures. T(K) 483 475 467 458 451 443 435 426 418 411 403 395 386 378 370 362 354 346 337 329 321 313 303

R_HF(Ohm) Q_HF(Farad) 31489 32009 32351 34208 36007 38575 43420 45377 49197 53501 57887 64232 72376 80289 89570 101560 115420 131490 147720 168660 190150 229090 249080

10-11

1.334 1.538 10-11 1.273 10-11 1.297 10-11 1.285 10-11 1.406 10-11 1.485 10-11 1.441 10-11 1.524 10-11 1.576 10-11 1.516 10-11 1.457 10-11 1.406 10-11 1.343 10-11 1.257 10-11 1.306 10-11 1.273 10-11 1.179 10-11 1.164 10-11 1.159 10-11 1.073 10-11 1.035 10-11 1.09 10-11

n_HF 0.946 0.937 0.949 0.948 0.948 0.942 0.938 0.940 0.936 0.934 0.936 0.938 0.94 0.942 0.946 0.943 0.945 0.949 0.95 0.95 0.954 0.956 0.952

_HF(second) 10-7

1.822 1.853 10-7 1.874 10-7 1.980 10-7 2.086 10-7 2.236 10-7 2.524 10-7 2.636 10-7 2.867 10-7 3.125 10-7 3.375 10-7 3.746 10-7 4.218 10-7 4.672 10-7 5.198 10-7 5.907 10-7 6.708 10-7 7.591 10-7 8.542 10-7 9.739 10-7 1.092 10-6 1.310 10-6 1.425 10-6

R_BF(Ohm) Q_BF(Farad) 19126 23700 27562 29175 41154 40563 49704 47905 56075 58471 64930 80192 94051 113540 136960 151160 165640 128630 241020 265240 251170 332190 372520

10-9

2.989 2.052 10-9 2.299 10-9 2.301 10-9 2.727 10-9 1.783 10-9 1.604 10-9 1.532 10-9 1.493 10-9 1.698 10-9 1.55 10-9 1.599 10-9 1.5 10-9 1.699 10-9 2.01 10-9 1.365 10-9 1.184 10-9 9.2 10-10 1.47 10-9 1.242 10-9 1.495 10-9 1.71 10-9 1.102 10-9

n_BF 0.863 0.905 0.891 0.889 0.877 0.916 0.928 0.929 0.938 0.934 0.936 0.933 0.936 0.923 0.903 0.944 0.954 0.966 0.928 0.946 0.915 0.902 0.962

_BF(second) 1.220 10-5 1.718 10-5 1.933 10-5 2.028 10-5 3.151 10-5 3.009 10-5 3.857 10-5 3.535 10-5 4.487 10-5 5.193 10-5 5.384 10-5 6.732 10-5 7.714 10-5 9.425 10-5 1.144 10-5 1.250 10-5 1.306 10-5 8.590 10-5 1.911 10-5 2.096 10-5 1.809 10-5 2.532 10-5 3.029 10-5

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Nickel doped ZnTe thin films were prepared by RF- sputtering on glass substrates; The films was characterized by UV-Visible spectrophotometer, and X-Ray diffraction for the optical and structural properties; The electrical properties were investigated by impedance spectroscopy.