Influence of Cd on structure, surface morphology, optical and electrical properties of nano crystalline ZnS films

Journal Pre-proof Influence of Cd on Structure, Surface Morphology, Optical and Electrical Properties of Nano Crystalline ZnS Films Sumanth Joishy, Albin Antony, P. Poornesh, R.J. Choudhary, Rajendra B.V

PII:

S0924-4247(19)31684-X

DOI:

https://doi.org/10.1016/j.sna.2019.111719

Reference:

SNA 111719

To appear in:

Sensors and Actuators: A. Physical

Received Date:

14 September 2019

Revised Date:

22 October 2019

Accepted Date:

2 November 2019

Please cite this article as: Joishy S, Antony A, Poornesh P, Choudhary RJ, B.V R, Influence of Cd on Structure, Surface Morphology, Optical and Electrical Properties of Nano Crystalline ZnS Films, Sensors and Actuators: A. Physical (2019), doi: https://doi.org/10.1016/j.sna.2019.111719

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Influence of Cd on Structure, Surface Morphology, Optical and Electrical Properties of Nano Crystalline ZnS Films

Sumanth Joishya, Albin Antonya, P. Poornesha, R. J. Choudharyb, Rajendra B. Va#

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Department of Physics, Manipal Institute of Technology, Manipal Academy of Higher Education,

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Manipal- 576104 India

UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017, India

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#Corresponding Author e-mail: [email protected]

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Highlights

The Zn1-xCdxS films with composition x< 0.40 have shown cubic phase with (1 1 1) prominent and others have shown a wurtzite structure with prominent (0 0 2) plane.

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The lattice constants, crystallite size, dislocation density and energy band gap evaluated The films exhibits free carrier absorption induced two photon absorption processes. The film resistivity decreased with increasing Cd content

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The films surface morphology change from grain to fiber structure with composition.

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ABSTRACT Transparent nano crystalline Zn1-xCdxS films were grown on glass substrates at 0.0125M precursor concentration using chemical spray pyrolysis technique. The suitable optimized temperatures were

adjusted from 673K to 573K for different compositions. The films with x< 0.40 have exhibited cubic phase with the crystalline plane of (1 1 1) orientation and for x> 0.30 have shown a hexagonal phase with (0 0 2) prominent plane. The lattice constants, crystallite size and dislocation density in the samples were estimated using X-ray diffraction data. The morphology of the films with higher Zn content exhibits fibrous structure and it changes to grain like structure on decreasing Cd concentration. XPS and EDAX analysis confirms the presence of elements in the deposits. The optical transmittance and energy band gap increased with increasing deposition temperature, whereas, decreased with

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increasing Cd dopant. The NLO behavior of the deposits indicates free carrier absorption induced two photon absorption processes. All deposits have shown n-type electrical conductivity. The film

resistivity decreases with increase in deposition temperature and Cd content. The obtained Zn1-xCdxS

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films are suitable for device application of gas sensor and optical limiter.

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Keywords: Nano crystallites, Cd-ZnS films, X-ray photoelectron spectroscopy (XPS), Z-scan,

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resistivity.

Introduction

Nano-crystalline ternary semiconductors of Zinc Cadmium Sulfide (ZnCdS) have potential applications in many opto-electronic devices[1-3]. Zinc Sulfide (ZnS) has a wide band gap of 3.7eV, good transparency in the visible range, large exciton binding energy (40 meV), non toxicity and it has

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received huge interest due to its chemical efficiency [4-6]. However, the electrical resistivity of pure ZnS film is very high (typically 108Ωcm), this can be overcome by doping with appropriate impurities [2, 6]. The small and direct energy band gap of Cadmium Sulfide (CdS) is the suitable candidate for the fabrication of CuInSe and CdTe film based optoelectronic devices [7]. However, in such applications, doping of CdS with wider band gap material and preparation method plays an important role in tuning optoelectronic properties of the films [8]. In solar cells, wide band gap ZnS is considered to substitute with CdS, resulting in increase of short circuit current by decreasing window absorption loss [9, 10].

The formation of Zn1-xCdxS ternary alloys by doping Cd ions in ZnS can efficiently modify the ZnS transport properties. The combination of CdS and ZnS is a typical example of increase of photocurrent and spectral response, decrease of window absorption losses with increase of optical energy band gap [11-14]. In addition, the technological developments in the field integrated optics have led to a new attention on the growth of new nonlinear optical (NLO) materials [15, 16]. To achieve the current requirements of nonlinear applications, materials having high nonlinear optical susceptibility are necessary. Although many transparent conducting thin films have been studied for optical nonlinearity,

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there is a need of investigation of transparent ZnCdS films, which plays a vital role in nonlinear optical devices.

A number of preparation methods such as vacuum vapor deposition [17], sputtering [18], pulse laser

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evaporation [19], electro deposition [20], screen printing [21], chemical bath deposition (CBD) [22], molecular beam epitaxial [23] and spray pyrolysis [24] have been reported previously. Among these

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techniques, spray pyrolysis is simple process with stable good reproducibility, large area deposition and adherent films can be obtained. Although many works have been done on the structure and transport

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properties of polycrystalline Zn1-xCdxS films, achieving high transparency with non- linearity property of these films is challenging. Hence, the main objective of the present work is to deposit highly

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transparent nano-crystallites Zn1-xCdxS (x = 0.00-1.00 at. %) films on glass substrate using low precursor solution molarity through spray pyrolysis technique. In addition, to find an optimized

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preparation condition for desired films, which are suitable for gas sensor and optical limiter application.

Experimental details

Thin films of Zn1-xCdxS (x = 0.00-1.00 at. %) were prepared using 0.0125M precursor solution

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concentration by spray pyrolysis technique. The solution was prepared by Cadmium chloride (CdCl2), Zinc chloride (ZnCl2) and Thiourea CS (NH2)2 which are the sources of Cd, Zn and S respectively. Analytical grade chemicals supplied by Sigma Aldrich, with a purity of 99.9% were used. Borosilicate glass slides with 2cm × 2 cm × 2 mm dimension were used as substrates which were cleaned by boiling in chromic acid for about 24 hours, and then cleaned with double distilled water. Later the substrates were dipped in the detergent solution for about 2 hours and then cleaned with double distilled water and NaOH solution. During the deposition the substrate to nozzle distance was fixed at 28 cm and the spray rate was kept constant (5ml/min). Since the vapor pressure of cadmium is greater than zinc, the

temperature was fixed according to the composition of the elements. With increasing Cd content in ZnS, the substrate temperature was kept in decreasing order from 673K to 573K. As the sprayed solution reached the heated substrate using air as a carrier gas with a pressure of about 5 kg/cm2, the pyrolytic decomposition of droplets have formed well adherent uniform Zn1-xCdxS films by adopting optimized preparation conditions. The preparation parameters (table 1) were optimized to get good quality films at a reasonable deposition time.

Characterization of films

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2.1.

The surface profilometer of Bruker Model no. DXT-18-1715(with accuracy ±5nm) was used to find the

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film thickness. The structural properties of deposits were found out with the help of Rigaku Miniflex 600, diffractrometer with CuKα source (1.5405Ǻ). Scanning Electron Microscopy (SEM) (Zeiss EVO

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18-15-57 was used to examine of surface morphology of the film. The elemental analysis was done through X-ray photoelectron spectroscopy (XPS) using Omicron energy analyzer (EA-125) with Al-Kα

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(1486.6eV) as a source of X-rays. Shimadzu-1800 UV-VIS spectrophotometer data were used for optical studies. Z-scan technique with a He-Ne laser at a wavelength of 632.8 nm and 20mW input power was used for analysis of nonlinear optical properties. The electrical property was studied by

Effect measurement setup. Result and discussion:

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using a Keithley 6220 source meter and magnetic field of 0.5Tesla by Van der Pauw method and Hall

3.1. Structure analysis

The CdS deposits grown at various temperatures have shown the hexagonal phase having high intense plane along (0 0 2) direction [fig.1(a)]. This type of alignment may be due to the controlled nucleation

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during the film formation [25]. Ashour et al [26] have also noticed the enhanced crystallization of CdS films with increasing deposition temperature. The film deposited at lower temperature had poor crystallinity. A sharp increase in the peak intensity with temperature might be ascribed to the heat induced orientated growth of crystallites. These results indicate the structural properties sensitively depend on deposition temperature. Compound semiconductors of II–VI group show structural duality by forming either hexagonal or cubic structures [27-28]. Fig.1(b) demonstrates the XRD results of Zn1-xCdxS films. The films with

x = 0.00-0.30 at. %, have shown the cubic phase with the prominent peak along (1 1 1) plane and there was no CdS related peaks. Similar result was also observed by Goudarzi et al [29]. Since the peaks were broad with low intensity; the high Zn content films had a low crystallinity level. The films with x> 0.30 at. % exhibited wurtzite structure with peaks assigned to (0 0 2), (1 0 0), (1 0 1), (1 1 0), (2 0 0), (1 1 2) and (1 0 2) planes of Zn1−xCdxS, indicating the structural change from cubic to hexagonal at higher concentration of Cd. The intensity of the plane gradually increased by Cd doping indicating increase of crystallinity. Due to large number of Zn ions, crystallites forming CdS phase start

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to grow through a different direction and the peaks were difficult to distinguish for the films with x=0.30-0.50. As the Cd amount increased, crystallites grow to give reflections from (1 0 0), (0 0 2) and

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(1 0 1) CdS planes having additional planes of (1 0 2), (1 1 0), (2 0 0) and (1 1 2). The diffraction peaks shifted towards smaller angles could be ascribed to difference in the ionic radii of Cd2+(0.92 Å) and

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Zn2+(0.60 Å). This indicates that the crystals obtained due to Zn1−xCdxS solid solution [30]. Since Cd is having high vapor pressure than Zn, the deposition temperature was optimized [table 1] according to

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the composition in order to reach the stoichiometry of Zn1−xCdxS films. The pure CdS and high Cd content ZnS films have shown better crystallinity than high Zn content films which is contradictory

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with the result of Idris et al [31] in which Zn0.80Cd0.20S and Zn0.40Cd0.60S films had better crystallinity. The obtained hexagonal Zn1−xCdxS ternary compound make it useful for window material for the fabrication of p-n junctions without lattice mismatch in devices based on quaternary materials like

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CuInxGa1−xSe2 or CuIn(SxSe1−x)2 [32].

The lattice constants for hexagonal and cubic structures were calculated by the following equations [27] 1 d2

=

3

a2 a

√(h2 +k2 +l2 )

+

l2

c2

(1)

(2)

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d=

4 h2 +hk+l2

Where d, a and (h k l) are inter planar distance, lattice constant and miller indices respectively. The increase of the lattice constant values with a deposition temperature (table 2), may be due to the variation in strain. The reduction in lattice strain of the deposited films with increasing temperature may be attributed to volume reduction by the annihilation of point defects such as self-interstitials and vacancies. The variation in lattice constants with increasing the Cd content shows that the replacement

of Cd atom having bigger ionic radii in comparison to Zn, that results a small increase in the lattice constant and leading to the increase of the volume of the unit cell. This may be due to the substitution of Zn by Cd atoms in the lattice. This linear increase in lattice constants with Cd doping confirms the homogenous solid solution formation of Zn1−xCdxS. Although, doping of Cd leads to an enhancement in the lattice parameter. This indicates that the samples were in a uniform state of stress with tensile component parallel to c-axis. The other possible reason for the increase might be due to the variation in the linear thermal expansion coefficients of film and glass. This is in agreement with the previous

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reports [33]. The size of the crystallite (D), dislocation density (δ) and numbers of crystallites per unit area of the

n D2

t D3

(4)

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N =

(3)

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δ=

0.9λ βcosθ

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D=

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deposits were calculated using the equation [34-35]:

Where λ is the wavelength of X- ray, n is a factor which equals unity, β is the full width half maxima, t is the film thickness. The average crystallite size increased with both increasing deposition temperature

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and Cd dopant (fig.2). An enlargement of crystallite size with temperature clearly demonstrates the enhancement of crystallinity with the deposition temperature. Increase in deposition temperature has resulted in growth of grains leading to increase of crystallite size. This can be due to the sharper convexity of smaller crystallites, which provide more area of connection among adjacent crystallites, enabling coalescence to form crystallites with larger size.

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The Cd doped ZnS has higher carrier density than ZnS due to high electron density of Cd than Zn. Thus, increasing Cd in films resulted in increased diffraction peak intensity by scattering more X-ray beams. On the other hand, there was a gradual decrease of dislocation density (fig. 2) with increasing deposition temperature and Cd dopant. This indicates the reduction of lattice imperfections concentration due to the reduced micro-strain within the films. These variations contrasts with the results of Al-Douri et al [36], where they have observed an increase of crystallite size and decrease of dislocation density with increasing Zn dopant in the CdS. The observed crystallite sizes are much lesser

than the previous results which is essential for gas sensing [37]. Hence, the ZnCdS films investigated here are suitable for gas sensor devices.

3.2. Morphological and compositional analysis The morphology of film grown at lesser deposition temperatures has shown voids and some pinholes (fig. 3). However, the films prepared at a higher temperature, the density of pinholes radically gets decreased and the films become an almost pinhole free. Besides, the crystallites agglomerated resulting

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in protrusion. The pure CdS has shown albumen and cauliflower morphology. Similar surface

morphology was also noticed by Jeevitesh et al [38] for CdO films of 0.2M and 0.5M concentration in

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which they have revealed the application of such type of morphology in oxygen sensing device. The influence of Cd enrichment in Zn1-xCdxS films indicates the improvement of the surface morphology of

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the deposits. The high Zn content films exhibited porous fibrous structure and it was changed to smaller granules with increasing Cd content. For x = 0.30 - 0.60, the structure appeared different shapes, that

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shows strong possibility of formation of Zn1−xCdxS alloy, as noticed from XRD result. However, the films of fibrous structure and smaller particle size are useful for gas sensing and photo catalyst application due to large surface area [39]. Borse et al [40] have observed the same kind of morphology

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for Cd1−xZnxS films deposited by solution growth technique.

The surface chemical composition of the deposits was observed by high resolution X-ray photoelectron

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spectroscopy (XPS) [fig. 4 (a)]. The binding energies of the Cd 3d5/2 , Cd 3d3/2, Zn 2p3/2 and Zn 2p1/2 peaks are 420.42 eV ,427.15 eV,1034.49 and 1057.58 eV respectively and the S 2p consists of a single peak at 241.97 eV. Hence, the XPS results confirm the presence of Cd, Zn and S in the deposit. Table 3 displays the elemental and compositional analysis carried through energy-dispersive analysis of

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X-ray (EDAX) spectrum [fig. 4 (b)]. The peaks of zinc, cadmium and sulfur were recognized. This approves the assimilation of Zn into the CdS matrix. But, Sulphur deficiency was noticed in all the deposits. Sulphur might have converted to SO2 due to its affinity towards oxygen, and this led to evaporate. An extra elements such as Si and Ca were eliminated, which were present due to glass substrates. 3.3. Optical properties

The optical transmittance [fig. 5 (a)] of the deposits was enhanced with increasing deposition temperature. This may be due to the gradual decrease in scattering of the light offered by the well arranged lattice crystallites. The relatively high transmittance at higher temperature and sharp fall of transmittance at absorption edge is an indication of less surface roughness and good homogeneity film. The blue shift of absorption edge with increasing temperature is due to the crystallinity improvement. The films with higher Zn content exhibited high transmittance and it was decreased with Cd doping [fig.5(b)], since the Cd atoms are coupled with the sulfur dangling bonds, that makes an energy gap to

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decrease in the localized states. The transmittance obtained in the present result is much greater than the previous reports [33, 41].

(6)

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(αhν)2 = A ( hν - Eg)n

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The energy band gap of the deposits is calculated from Tauc’s plot method [42]

Where, A is a constant, Eg is optical energy band gap and the value of n is equal to ½ since the

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transition in the present case is direct-allowed. The Eg values were found by extrapolating the linear portion of the spectrum to the photon energy axis as is shown in the fig 6. The energy band gap of the film increased with increasing deposition temperature. This may be due to Burstein-Moss effect, in

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which the Fermi level movement led to an increase in the carrier concentration when the substrate temperature was increased. Increase of temperature leads to an increase in carrier concentration. As the carrier concentration increases, light absorption by the carriers also increases, leading to the higher

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absorption coefficient [43]. This variation is contradictory with the result of Girish et al [44] where they have observed decrease of band gap of spray deposited CdS films with increasing temperature. The incorporation of Cd2+ into the ZnS has red shifted absorption peak indicating band gap narrowing (fig. 7). The doping of Cd in ZnS lattice site increases the excitonic energy of the Zn1−xCdxS thin films, and

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as a result, the absorption peaks shifted to a longer wavelength region with an increasing Cd dopant which is an indication of red shift. This is also an indication of the Zn1−xCdxS ternary compound formation. This is possibly due to the increased crystallite size (fig. 2), which lead to quantum confinement of the charge carriers and thereby decrease of band bending effect [45]. For less Cd incorporation, there was a gradual change in the energy band gap. At higher Cd concentrations, the band gap variation is more or less linear. The higher band gap values observed for the high Zn content in CdS films probably be due to the occupancy of Zn atoms in the CdS lattice and the quantum size effect as expected for the nano crystalline nature of the films. This means that thin film of CdS with

high Zn content allow more light of shorter wavelength to transmit. This makes it useful to improve efficiency of solar cell. Similar kind of reduction of band gap by Fe doping in ZnO was noticed by Goktas et al [46], in which they explain s-d spin-exchange interactions between the band electrons and the localized d electrons of the transition-metal ion. Urbach energy (Eu) and extinction coefficient (k) were estimated from below relations[47-48]: α = α0 exp(hν/EU)

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k = αλ/4π

(7)

Urbach energy [EU] was determined by finding the reciprocal of the slope of the linear portion of the

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curves(fig 8). The values of k decrease with increasing λ(fig. 9), but increases with Cd concentration in the thin films. The surface morphology has been improved with increasing Cd content due to the

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accumulation of more grains that resulted in high absorption of light. The behavior of extinction

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coefficient is almost similar which supports the argument that is correlated to the surface morphology.

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3.4. Nonlinear optical properties

The nonlinear optical properties of Zn1−xCdxS nanostructures at different Cd compositions have been investigated [49] by open aperture z-scan technique. All the films show positive absorption nonlinearity

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indicating reverse saturable absorption mechanism (RSA) in which the normalized transmission declines with increase in light intensity. Nonlinear absorption coefficient, βeff of the investigated films were calculated by the formula α0 = α + βeff I

(9)

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Where I is the laser beam intensity and α is the linear absorption coefficient of the film. The open aperture (OA) Z-scan traces of the Zn1−xCdxS films are shown in fig.10. The signature of the RSA process in the films can be ascribed to any of the phenomena such as two photon absorption (TPA), free carrier absorption (FCA), induced nonlinear scattering etc. The energy of light used for the excitation of ZnCdS thin film is lesser than the Eg but larger than Eg/2, that satisfies the condition for TPA mechanism. Even though, since the material in the present investigation comes under resonant non linearity the nonlinear absorption is arising from a sequential process of FCA induced TPA mechanism.

The calculated values of βeff and corresponding imaginary part of third order susceptibility χ (3) were reported in table 4. From the open aperture z-scan analysis it is observed the effect of scattering in the films becomes more effective as Cd doping decreases which results in a decrement nonlinear optical parameter. The highest nonlinear absorption coefficient βeff was observed for 0.8 at.% Cd doping which started decreasing at lower Cd doping. The variation induced on surface morphology of the films upon varying Cd incorporation can be a possible reason for these effects. From the SEM (fig 3) analysis, Zn1-xCdxS

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lattice upon reducing the Cd content give rise to agglomeration of grains without well-defined

structure. These growth results in the prominent scattering effects which will affect open aperture Z-

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scan traces. The calculated values of βeff and third order susceptibility χ(3) were reported in table 4.Since the nonlinear optical scattering is becoming prominent in lower doping percentage of Cd the nonlinear

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equations based on TPA mechanism used for calculating nonlinear absorption coefficient βeff and Im χ(3) does not valid. Therefore in the present study we restricted the calculation of βeff and Im χ(3) till

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0.6 at.% Cd doping. The higher nonlinear absorption coefficient observed in lower Cd doping

3.5. Electrical properties

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concentration (1.00 to 0.80 at.%) features the reliability of grown films in optical limiting applications.

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The resistivity of the Zn1-xCdxS deposits was found to decrease (table 5) with increasing Cd dopant which is due to enhancement of carrier concentration in the deposits. The corresponding decrease of surface area due to the growth of crystallites may be responsible for the decline of film resistivity with increasing Cd. Thus, the reduction in resistivity of the films is due to the improvement of grain size. The bigger grain sizes, which decrease the grain boundary surface area, are responsible for the increase

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of carrier mobility. All the deposits have shown n-type conductivity. The increase of charge carrier concentration with Cd doping is attributed to the decrease of stacking fault density and miss-orientation of the crystallites [50].Similar type of observation was noticed by Reddy et al [51] for ZnxCd1-xS films deposited by spray pyrolysis at 673K. In ZnS films the inter-grain barrier height decreases with Cd dopant [52], which is caused by the increasing size of the crystallite. Zn1-x CdxS films of 0.05M concentration deposited by Idris et al [31] at 523K, in which there was no monotonically decrease or increase of resistivity with increasing Cd doping. The increase of Cd concentration in ZnS makes the

perfection in the lattice structure which leads to decrease of grain boundary scattering and hence the concentration of charge carrier and electrical conductivity are enhanced. Table 6 indicates the comparison of Zn0.40Cd0.60S film result with previously published reports. 4.

Conclusion

Transparent nano crystalline Zn1-x CdxS (x=0.00-1.00 at. %) films were deposited on glass substrates at optimized temperature through chemical spray pyrolysis method. The films having x< 0.40 and x>50% reveals cubic and hexagonal phases respectively. Increase of deposition temperature and Cd

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concentration has led to the growth of crystallites with decrease in dislocation density and the number of crystallites per unit area. Increase of deposition temperature has enhanced surface morphology and

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the grain size with different structures were noticed at different Cd concentrations, whereas high Zn content, films exhibits wrinkled fibrous structure. The XPS and EDAX spectra confirmed the presence

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of Cd, Zn and S elements in the deposits. The energy band gap were increased with increasing substrate temperature, whereas it decreased with Cd doping due to Burstein-Moss effect. The Urbach energy and

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extinction coefficient values for the deposits were varied with increasing temperature and Cd dopant. The NLO behavior of the films indicates the materials exhibit FCA induced two photon absorption

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mechanisms. Reduction of resistivity in the films on increasing deposition temperature and Cd concentration were due to increase in charge carrier concentration. The high transmittance and superior NLO properties of Zn1-xCdxS films makes promising material for nonlinear optical device and high

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resistivity due to smaller crystallite size of fibrous structured Zn1-xCdxS [x<0.60] films appropriates for use in resistive mode gas sensor applications. Declaration of interests

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☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Acknowledgements:

Mr. Sumanth Joishy is thankful to Manipal Institute of Technology, for granting Senior Research Fellowship and providing research facilities. Authors also thankful to UGC-DAE CSR, Mumbai

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Center, India for financial support.

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Cd1− xZn xS thin films for solar cell applications, Thin Solid Films. 431 (2003) 349-353. [49] M. Sheik-Bahae, A. ASaid, T. H.Wei, D. J.Hagan,E. W.Van Stryland, Sensitive measurement of

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optical nonlinearities using a single beam, IEEE J. Quantum Electron. 26 (1990) 760-769. [50] L. L. Kazmerski, W. B. Berry, C. W. Allen,Role of defects in determining the electrical properties of CdS thin films, J. Appl. Phys. 43, (1972) 3515. [51] K. T. R. Reddy, P. J. Reddy, Studies of ZnxCd1-xS films and ZnxCd1-xS/CuGaSe2 heterojunction

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solar cells,J. Phys. D: Appl. Phys.25, (1992) 1345-1348. [52] B. Metin, K. Refik, O. Mustafa, Effect of the Zn Concentration on the Characteristic Parameters of Zn{x}Cd{1 - x}S Thin Films Developed by Spraying Pyrolysis Method Under the Nitrogen Atmosphere, Turk J. Phys. 26 (2002) 121. [53] M. Celalettin Baykul, Nilgun Orhan, Band alignment of Cd(1−x)ZnxS produced by spray pyrolysis method, Thin Solid Films 518 (2010) 1925–1928.

[54] S. Azizi, H. Rezagholipour Dizaji, M.H. Ehsani, Structural and optical properties of Cd1-xZnxS (x = 0, 0.4, 0.8 and 1) thin films prepared using the precursor obtained from microwave irradiation processes, Optik 127 (2016) 7104–7114. [55] V.B. Sanap, B. H. PAWAR, Study of chemical bath deposited nano crystalline CdZnS thin films,

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Author Biographies

Sumanth Joishy

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Sumanth Joishy is a Research Scholar in department of Physics at Manipal Institute of Technology, Manipal Academy of Higher Education. He received his Master’s in Physics from Manipal Academy of

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Higher Education. His research interests include Semiconducting thin films, Opto electronic devices, Gas sensors, Photoresponse and Third Nonlinear Optical Properties of thin films. He has over 5

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publications in peer reviewed journal

Albin Antony

Albin Antony is a research scholar in the department of Physics at Manipal Institute of Technology, Manipal Academy of Higher Education. His research focuses mainly on tuning the third order nonlinear optical properties of semiconductor nanostructures by electron beam irradiation. He has

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received his Master’s in Physics from Manipal Academy of Higher Education in 2016.

Poornesh P.

Poornesh P is an Assistant Professor in department of Physics at Manipal Institute of Technology, Manipal Academy of Higher Education. He received his Master’s in Physics from Manglore University and Ph.D. degree from National Institute of Technology, Karnataka. His research interests include Third Nonlinear Optical Properties of Polymers, Semiconductors, Optical Power Limiting Materials for

Eye and Sensor Protection, Second Harmonic Generation in Organic Crystals and Metal Oxide Semiconductor based Gas Sensors. He has over 50 publications in peer reviewed journals.

R. J. Choudhary R.J.Choudhary is a scientist F in SQUID-VSM and PLD Lab in UGC UGC-DAE Consortium for

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Scientific Research and has published several papers in peer reviewed journals.

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Rajendra B.V

Rajendra B V is an Associate Professor- Senior Scale in the department of Physics at Manipal Institute

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of Technology, Manipal Academy of Higher Education. He received his Master’s in Physics from Manglore University and Ph.D. degree from National Institute of Technology, Karnataka. His research interests include preparation of characterization of thin films, fabrication and characterization of

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semiconductor devices, characterization of spintronic and photonic materials.

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publications in peer reviewed journals.

He has over 20

Fig. 1: XRD patterns of (a) CdS thin films grown at different deposition temperatures and

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b2)Zn1-xCdx S(x=0.00-1.00) thin films deposited using 0.0125M

(b1,

Fig. 2:Crystallite size and dislocation density versus (a) substrate temperature of CdS films and (b) Cd

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concentration in Zn1-xCdxS films

Fig.3: SEM images of(T1-T4) CdS films grown at different deposition temperatures andZn1−xCdxS

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films of different x (0.00-1.00)values.

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Fig.4(a): Typical XPS spectra of Cd0.50Zn0.50S polycrystalline thin film.

Fig. 4(b) : Typical EDS spectrum recorded for Zn0.50 Cd0.50S film

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Fig. 5: Transmittance spectrum of (a) CdS films grown at variousdeposition temperatures and (b) Zn1-x

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CdxSfilms with various x values using 0.0125M solution molarity at optimized deposition temperature.

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Fig. 6: (αhν)2 versus hυ plot of (a) CdS films grown at variousdepsoition temperatures and (b) Zn1xCdxS

films with various x values using 0.0125M concentrations.

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Fig.7: Optical energy band gap energy as a function of Cd concentration in ZnS films.

Fig .8:Variation of ln (α) versus photon energy of (a) CdS films grown at different deposition

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temperatures and (b) Cd1-xZnxS films of 0.0125M concentration.

Fig.9:Variation of extinction co-efficient (K) with wavelength of (a) CdS films grown at different

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deposition temperatures and (b) Cd1-xZnxS films of 0.0125M concentration.

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Fig.10:Open aperture Z-scan trace of Zn1−xCdxS (0-20%) thin films prepared using 0.0125M solution molarity.

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Table 1: Optimized parameters used to deposit Zn1-xCdxS films

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Cadmium chloride, Zinc chloride and Thiourea Double distilled water 0.0125M x = 0.00 – 1.00 at. % 5kg (f) /cm2 5 ml/min x=0.00-0.50 x=0.60 x=0.70 x=0.80 x=0.90 x=1.00 673K 653K 633K 613K 593K 573K 28cm 500-550nm

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Solute Solvent Molarity of solution Doping concentration (Cd) Air pressure Solution spray rate Optimized substrate temperatures Nozzle to substrate distance Film thickness

Samples

Table 2: Calculated structural parameters of Zn1-xCdxS films

Sample code

Substrate temperature (K)

Lattice constant (Ǻ) Hexagonal

Cubic

Number of crystallites per unit area ‘N’ ( ×1016cm-2)

ZnS

ZSA

673

a = 5.269

674

Zn0.90Cd0.10S Zn0.80Cd0.20S

ZCSA1 ZCSA2

673 673

a =5.271 a = 5.280

385 256

Zn0.70Cd0.30S

ZCSA3

673

a =5.332

118

Zn0.60Cd0.40S

ZCSA4

673

a=3.825c=6.205

51.5

Zn0.50Cd0.50S

ZCSA5

673

35.8

Zn0.40Cd0.60S

ZCSA6

653

a=3.843 c=6.259 a=3.856

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24.8

c=6.299 a=3.876 c=6.340

Zn0.20Cd0.80S

ZCSA8

613

a=3.880 c=6.354

Zn0.10Cd0.90S

ZCSA9

593

CdS

CSA

T1 483

a=3.914 c=6.419 a=3.940 c=6.445

16.4

T3 543

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T4 573

11.9 41.9

a=3.946 c=6.449 a=3.950 c=6.454 a=3.953 c=6.456

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19

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633

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ZCSA7

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Zn0.30Cd0.70S

16 10.4

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Table 3: Atomic percentage of constituent elements in Cd1-xZnxS thin films Film composition

Atomic percentage precursor solution

in Atomic percentage deposited film

in

ZnS Zn0.90Cd0.10S

Zn 50 45

Cd 00 05

S 50 50

Zn 50.90 46.36

Cd 00 5.74

S 49.10 47.90

Zn 0.80Cd0.20S

40

10

50

43.26

9.55

47.19

Zn 0.70Cd0.30S

35

15

50

35.27

16.06

48.67

the

30 25

20 25

50 50

30.35 23.59

20.76 27.66

48.89 48.75

Zn 0.40Cd0.60S

20

30

50

21.09

30.88

48.03

Zn 0.30Cd0.70S

15

35

50

16.11

35.98

47.91

Zn 0.20Cd0.80S

10

40

50

10.89

41.00

48.11

Zn 0.10Cd0.90S CdS

05 00

45 50

50 50

5.03 00

46.07 53.54

48.90 46.46

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Zn 0.60Cd0.40S Zn 0.50Cd0.50S

χ(3)Img

βeff(cm/W)

1.00

4.01×10-1

0.90

2.50×10-1

1.316×10-3

0.80

3.90×10-1

2.055×10-3

0.70

1.54×10-1

0.812×10-3

1.94×10-1

1.024×10-3

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0.60

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Cd concentration (at. %)

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Table 4: Nonlinear optical values of Zn1−xCdxS thin films

2.113×10-3

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Table 5: Electrical resistivity of Zn1-xCdxS films prepared using 0.0125M solution molarity. Dopant

Resistivity

Carrier concentration n

(Cd) %

[Ωcm]

(cm-3)

2.08× 108

2.2 × 1013

20

9.60 × 108

4.50 × 1013

40

1.63 × 106

2.5 × 1015

60

2.25 × 106

8.1 × 1015

80

1.05 × 104

1.12 × 1016

100

4.55 × 103

1.45 × 1016

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Table 6: Comparison of Zn0.40Cd0.60S film result with previous reports

Technique

Structure

Surface morphology

Transmittanc e[%]

Band gap [eV]

NLO study

Resistivity [Ωcm]

Spray pyrolysis

Hexagonal

Spherical grains

~75

2.77

2.25× 106

Baykul et al [53] Azizi et al [54]

Spray pyrolysis Microwave irradiation method Chemical bath deposition

Hexagonal

─

2.83

FCA induced TPA mechanisms ─

Mixture of hexagonal and cubic Mixture of hexagonal and cubic

Grains

2.51

─

─

Hexagonal

Grains

─

~65

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3.35

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─

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Mariappan Chemical et al[37] bath deposition

~70

2.5

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Sanap et al [55]

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Reports and Reference Present study

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─

─

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