Synthesis and characterization of structural, morphological and photosensor properties of Cu0.1Zn0.9S thin film prepared by a facile chemical method Ghamdan M. M. Gubari, Ibrahim Mohammed S. M., Nanasaheb P. Huse, Avinash S. Dive, and Ramphal Sharma
Citation: AIP Conference Proceedings 1953, 100014 (2018); doi: 10.1063/1.5032950 View online: https://doi.org/10.1063/1.5032950 View Table of Contents: http://aip.scitation.org/toc/apc/1953/1 Published by the American Institute of Physics
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Synthesis and Characterization of Structural, Morphological and Photosensor Properties of Cu0.1Zn0.9S Thin Film Prepared by a Facile Chemical Method Ghamdan M. M. Gubari1, Ibrahim Mohammed S. M1., Nanasaheb P. Huse1, Avinash S. Dive1 and Ramphal Sharma 1,a) 1
Thin Film and Nanotechnology Laboratory, Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431004, Maharashtra, India a)
Corresponding author:
[email protected]
Abstract. The Cu0.1Zn0.9S thin film was grown by facile chemical bath deposition (CBD) method on glass substrates at 60 °C. The structural, morphological, photosensor properties of the as-grown thin film has been investigated. The structural and phase confirmation of the as-grown thin film was carried out by X-ray diffraction (XRD) technique and Raman spectroscopy. The FE-SEM images showed that the thin films are well covered with material on an entire glass substrate. From the optical absorption spectrum, the direct band gap energy for theCu0.1Zn0.9S thin film was found to be~3.16 eV at room temperature. The electrical properties were measured at room temperature in the voltage range ±2.5 V, showed a drastic enhancement in current under light illumination with the highest photosensitivity of ~72 % for 260 W. Keywords: Cu0.1Zn0.9S, Thin film, Chemical bath deposition, Raman spectrum, Photosensitivity.
INTRODUCTION Nanostructures and thin films of binary I-VI and II–VI compound materials i.e. CuS-ZnS have been enormously studied recently. ZnS is an n-type semiconductor material, and it is the most important material having wide energy direct band gap (Eg = 3.65 eV) 1, 2. Thus, it could be used for the fabrication of optoelectronics devices, such as blue light-emitting diodes etc 2. CuS is a p-type semiconductor with an important direct band gap semiconductor. It has a wide variety of band gap ranging from 1.2 eV to 2.5 eV 3. Copper sulfides can find applications in photo thermal conversion, solar cell devices, coatings for microwave shields, also it has various optoelectronic properties for the solar control 3. The mixing of ZnS and CuS will provide extensive absorption range and enhanced absorption of the solar spectrum 4. Cu0.1Zn0.9S (CZS) is p-type ternary alloy compound being promising materials for a variety of optical device applications. Different techniques have been used for the Cu0.1Zn0.9S thin films deposition, such as spray pyrolysis1, 5 and SILAR 2. In the present work Cu0.1Zn0.9Sthin film was synthesized by facile chemical bath deposition (CBD) method and studied its structural, morphological and photosensor properties.
EXPERIMENTAL The Cu0.1Zn0.9S thin films were grown on glass substrates from a basic bath containing solutions of 0.1 M cupric chloride (CuCl2), 0.9 M zinc chloride (ZnCl2), 2 M thiourea, (SC(NH2)2), EDTA and triethanolamine. The separately prepared solutions of cupric chloride, zinc chloride and thiourea in deionized water (40 mL each) were stirred vigorously for 5 min. Then added few drops of (2 drops) Triethanolamine, (10 drops) EDTA as a complexing agent into solutions of Zn-Cu respectively. After that, the pH of the solution was adjusted to ~11 by drop wise addition of ammonia solution into a source of zinc. Finally, mixed all solutions together under stirring until the solution becomes
2nd International Conference on Condensed Matter and Applied Physics (ICC 2017) AIP Conf. Proc. 1953, 100014-1–100014-4; https://doi.org/10.1063/1.5032950 Published by AIP Publishing. 978-0-7354-1648-2/$30.00
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blue dark. The deposition was carried out at a temperature of 60°C by keeping the beaker in a water bath for 30 min. The obtained thin film was washed and rinsed with deionized water and dried subsequently in the air. Such thin films were examined for structural, morphological and photosensor properties.
RESULTS AND DISCUSSION The as-grown Cu0.1Zn0.9S thin films were characterized by X-ray Diffraction Pattern (XRD), recorded on X-ray Diffractometer, BRUKER (D8-Advance) with CuKα1 radiation (λ= 1.5406Å). Field Emission Scanning Electron Microscopy (FE-SEM) HITACHI S-4800 used to examine the surface morphology. The Raman spectrum was recorded in the range of 200 to 2000 cm-1 using STR Raman spectrometer system (SEKI TECHNOTRON Corporation, Tokyo) with 532 nm line of an argon gas laser at a power level of 500 W. The optical absorption spectra in the wavelength range of 300–800 nm were recorded using UV-Vis Spectrophotometer (Perkin Elmer, LAMDA 25). Electrical measurements of the samples were studied by I-V (current–voltage) measurement system of Keithley 2400 interfaced with class AAA Solar simulator.
Structural studies Fig. 1(a) show the XRD pattern of as-grown Cu0.1Zn0.9S thin film onto a glass substrate. The peaks at 2θº values 26.51º, 28.76º, 29.97º, 46.49º and 57.84º correspond to the (100), (101), (103), (110) and (311) planes respectively. All peaks are compared with the standard JCPDS data and are well matched with the hexagonal phase of CuZnS thin film (JCPDS # 80-0007& 06-0464) 6. The calculated lattice parameters were a = 3.80 Å and c = 5.66 Å. The average crystalline size was determined by using Debye Scherer’s formula as given in Eq. (1) which was ~37 nm. The dislocation density and strain were calculated by the Eqs. (2) and(3) respectively and the estimated values are given in Table 1. =
. �
… (1);
=
�
… (2);
=
… (3)
Where D is the crystallite size estimated for the (hkl) reflection, λ is the X-ray wavelength (1.5406 Å), β is the full width at half maximum (FWHM) of the peak, Ɵ is the Bragg angle, ε is the strain and δ are the dislocation density.
FIGURE 1 (a): Shows the XRD and (b)show Raman spectrum of Cu0.1Zn0.9S thin film.
The Raman spectrum of the Cu0.1Zn0.9S thin film is shown in Fig. 1(b). At the G point of the Brillouin zone, the A1 + E1 +2E2 modes are Raman active based on the group theory analysis. The peaks at 343, 408, 465, 555 and 655 cm−1 correspond to 2-E2 (M), A1 (TO), E1 (TO), E2 (High), E1 (LO), and A1modes, respectively. The intensive E2 High mode at 465 cm−1 indicates that the preferred growth direction of Cu into ZnS nanostructures.1, 7, 8
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Surface morphology The morphology of the synthesized Cu0.1Zn0.9S nanostructured thin film was studied using Field emission scanning electron microscopy as shown in Fig. 2 at different resolutions. The FE-SEM image shows spherical shape morphology of the CZS thin film. The spherical grains are homogeneous and uniformly distributed with narrow size distribution throughout images (at resolution 2 μm). 2Ɵ
26.51 28.76 29.97 46.49 57.84
Planes (hkl)
Interplanar spacing Å
Crystallite Size D (nm ) 24.14 34. 71 39.24 31.22 56.32 37.1
(100) 3.36 (101) 3.10 (102) 2.98 (110) 1.95 (311) 1.59 Average values
δ (1015) lines/m2
1.72 0.83 0.65 1.03 0.32 0.91
ε (103 ) 0.19 0.04 0.05 0.06 0.03 0.07
Table 1: The estimated structural parameters of as-grown Cu0.1Zn0.9S thin film.
FIGURE 2: Show FE-SEM obtained from Cu0.1Zn0.9S thin film at different resolutions
Optical Studies Fig. 3 shows optical absorption spectrum recorded as a function of wavelength vs. absorbance for as-grown Cu0.1Zn0.9S thin film, which was further used to compute the band gap. Optical absorption by the thin film was studied in the wavelength range of 300–800 nm. The inset Fig. 3 shows the Tauc’s plot plotted between (αhυ)2 vs. photon energy (hυ) to obtain direct band gap value estimated by extrapolating the linear part of the plot. From the optical absorption spectrum is given in Eq. (4), clear band edge around ~392 nm was observed which results in a direct energy band gap of ~3.16 eV, Which is in good agreement with the band gap values reported by others researchers 6 and so as to use it as absorber or window layers.
FIGURE 3: UV absorption spectrum obtained from Cu0.1Zn0.9S thin film and the inset the Tauc’s plot.
=
(
FIGURE 4 (a): J-V characteristic curve of the Cu0.1Zn0.9S thin film in dark and in light (80-260W) and (b)Shows a plot of photosensitivity and photoresponsivity vs. light intensity. −
)
(4)
Where n is a constant equal to 1/2 for direct band gap and 2 for indirect band gap materials, Egis the energy band gap, h is the Planks constant and ν is the frequency of incident light.
Photosensor Studies Fig.4 (a) shows current density versus voltage (J-V) plots of the Cu0.1Zn0.9S thin film for dark condition and various illumination intensities from (80 W to 260 W). The Cu0.1Zn0.9S thin film shows a photosensitivity of ~72%, change in photocurrent 0.134 mA and photoresponsivity 0.52 μA/W for 260 W, this estimated using Eqs.(5-7). From Table 2 the photosensitivity, photoresponsivity, Photosensor Efficiency and change in photocurrent are increased with increased of Intensity of light from (80 W to 260 W) shown in Fig. 4(b).3, 9
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% =
−
×
… (5);
=
… (6) ;
=
−
….(7)
Where, Rd stand for resistance in dark, R l stand for resistance in light, Ip is the photonic current, Id is the dark current, s stand for effective film area and P i is the power of the incident light per unit area. TABLE 2: Photosensing properties of as-grown Cu0.1Zn0.9S thin film calculated at different light intensities. Intensity of light (Watt) 80 140 200 260
Photosensitivity (S) (%)
Photosensor Efficiency (P)
Photoresponsivity (R ) (μA/W)
11.33 21.18 42.35 72.10
1.13 1.27 1.73 3.59
0.05 0.07 0.48 0.52
Change in Current (mA) 0.006 0.013 0.031 0.134
Resistance(kΩ) Dark 96.24 96.24 96.24 96.24
Light 85.33 75.85 55.48 26.48
CONCLUSIONS Chemical bath deposition method was used for the successful preparation ofnanocrystallineCu0.1Zn0.9S thin film on glass substrate. The XRD study showed the hexagonal structure of the Cu0.1Zn0.9S thin film. The Raman spectrum was intensified E2 High mode at 465 cm−1 indicates that the preferred growth direction of Cu into ZnS nanostructure. The FE-SEM morphology reveals that substrate is well covered and average grain size was ~37 nm. The optical study reveals sharp band edge around ~392 nm results in the wide band gap of ~3.16 eV. The electric study reveals the Photosensor efficiency, photoresponsivity and photosensitivity were found to be 3.59, 0.52 μA/W and 72.1 % for 260 W respectively. These reported results suggest that CZS thin film is a promising material for the optoelectronic device and solar cell application.
ACKNOWLEDGEMENTS Authors are thankful to The Head, Department of Physics and Department of Nanotechnology, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad for providing necessary lab facilities.
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