International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
Structural and Optical Properties of CdS:In
Nanoparticle Thin Films Prepared by CBD
Technique
Hamid S. Al-Jumaili1 and Taha N.mahmood2
Physics Department, College of Education for Pure Science, University of Anbar, Iraq.
ABSTRACT
CdS and CdS:In nanoparticle thin films were deposited on a glass substrate by chemical bath deposition (CBD) at bath
temperature of 70 °C and a pH of 10 for 60 min deposition time. The structural and optical properties of the as-deposited film
were characterized using XRD, AFM, and UV-VIS spectrophotometry techniques. The peak intensities observed in the XRD
patterns were similar to consistent with the polycrystalline hexagonal structure of the undoped and 0.1% In-doped CdS films.
Additionally, the greater patterns of the doping ratio the amorphous nature of CdS:In films. The grain size of the films was found
to ranged from 2nm to 3nm, which was-measured by XRD analysis. The AFM morphology study results of CdS and CdS:In
conformed to the greater grain size and dense morphology of the thin films. The grain size found by AFM analysis ranged
between 36nm and 67nm depended on In concentrations. The direct optical band gap of the undoped CdS film was 3.84 eV,
whereas that of the In-doped CdS films decreased to 3.64 eV and then increased to 3.79 eV at 5% In doping.
Keywords: CdS:In thin film, CBD method , nanoparticle thin film, structural and optical properties.
1. INTRODUCTION
Doping of nano materials with sutable impurities such as In and Al, has given rise to a new class of nano materials whose
structural, optical and electrical properties differ from those of the corresponding host nano-materials [1,2]. These
dopants form deep trap levels and act as luminescence centers. Indium is a one of the more effective dopant in obtaining
n-type CdS with low resistivity and high optical transmittance [3,4]. The indium, which shows a donor behavior, is often
used as an ohmic contact material to CdS [5]. The doped CdS thin films are also important for fabrication of a gas sensors
and photovoltaics [6-7]. Chemical bath deposition (CBD) is extensively used as a method for the preparation of thin-film
materials. The CBD is a simple, as well as low-temperature, and in expensive large-area deposition technique [7].The
deposition of CdS using CBD is based on the slow release of Cd+2 ions and S−2 ions in aqueous alkaline bath and the
subsequent condensation of these ions on the substrates that are suitably mounted in the bath. The slow release of Cd+2
ions is achieved by adding a complexing agent (ligand) to the Cd salt to form some cadmium complex species, which,
releases small concentrations of Cd+2 ions upon dissociation. The S−2 ions are supplied by the decomposition of thiourea
or sodium thiosulfate [8]. This study aimed to prepare nano CdS:In thin films by CBD. Additionally, this work studied
the influence of CBD on the structural and optical properties of CdS:In thin films.
2. EXPERIMENTAL
CdS and CdS:In thin films were deposited on a glass slides using the CBD technique. A bath containing (0.1 M)
solutions of indium chloride (InCl3) , cadmium chloride (CdCl2), and thiourea CS(NH2)2 was developed, and the pH of
the solution was adjusted to 10 by the addition of NH4OH. Glass slides were cleaned using liquid detergent in an
ultrasonic bath, dipped into a chromic acid bath for 2 h at room temperature, washed with distilled water and acetone,
and then dried. The glass substrates were immersed vertically in the reaction vessel, and the bath was set to the desired
temperature. Deposition was carried out at 343 K for 60 min, and the slides were left in the bath for 24 h at room
temperature. The nano CdS film was doped with 1%,3% and 5% In .The deposited films were then washed with distilled
water in an ultrasonic bath and were dried in air. The crystallinity phase and orientation of the CdS and CdS:In films
were determined by XRD using a Philips PW 1840 instrument with a Cu-Kαtarget. The morphology of the films was
determined by AFM (AA 3000 Angstrom Advanced Inc.). A UV-VIS spectrophotometer (Jenway 6800) was used to
measure the absorbance and transmittance of the films in the wavelength (λ) range from 300 nm to1100 nm; the optical
energy gap was calculated from these measurements.
3.RESULTS AND DISCUSSION
3.1 Structural and analysis of CdS and CdS:In thin films.
The XRD spectra of the undoped and In-doped nanostructure CdS films are shown in Fig.(1). The patterns for both CdS
and CdS:In films displayed the diffraction peaks of the hexagonal CdS with the preferred orientation in the (111)
Volume 2, Issue 10, October 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
direction, along with the polycrystalline structure of the undoped and 0.1% In-doped CdS films. Mean while, the change
in structure of the amorphous films at higher doping concentration is also shown in Fig.(1). The diffraction peak existed
at 2θ = 26.2° and 2θ = 26.9° for CdS and 0.1% CdS:In respectively. These values of 2θ and their crystal planes are
comparable to the standard data of CdS matches well (ASTM File No. 100454, 411049). Similar results were observed by
CBD, as reported in the literature [9,10].
The grain size (D) of CdS film was estimated using Debye-Scherrer’s formula, [11]
Dhkl=Aλ/βcosθ …………………………(1)
Where λ is the X-ray wavelength, A is a constant , β is the full-width at half-maximum (FWHM) of the peak, and θ is the
Bragg angle. The grain size of the CdS film was found to be (2nm to 3nm) for the (111) direction as shown in Table (1).
These results agreed with those of several studies [8,12]. The diffusion doping of nanostructure CdS film by indium does
not change the average grain size (D) of the films, but decreases its crystallinity.
Figure (1): The X-ray diffraction patterns of CdS:In thin films a-without doping
b- 1% doping c- 3% doping d- 5% doping .
Table (1): The obtained Results of XRD for CdS and CdS:In thin films.
3.2. Morphological analysis
To investigate the morphology of CdS and CdS:In thin films deposited on glass substrate, atomic force micrographs
(AFM) were recorded for 2×1 cm2 regions. Figure (2) shows an AFM image of the CdS and CdS:In thin films. The image
shows that the thin film is homogenous, without any cracks and continuous with very well connected small grains. The
value of the roughness and the root mean square surface values for the undoped CdS are 3.78 and 4.7 nm respectively,
Meanwhile, the roughness values for the doped CdS are 1.94, 2.52 and 4.04 nm. The root mean square of the surface
values are 2.32, 2.95 and 4.72 nm with 1%, 3% and 5% In doping respectively. The AFM analysis showed that the films
have nanoparticles with decreased surface thickness with dopant addition from 31.35 nm of the undoped CdS to 11.54,
14.20 and 20.37 nm for 1%,3% and 5% In doping of CdS respectively. In the AFM analysis, the average grain size of the
undoped CdS is 40 nm , whereas that for the doped CdS are 36, 56.09 and 67.53 nm at 1%, 3% and 5% In doping
respectively. These values are greater than those obtained by XRD, which agreed with the values reported by other
researchers.[12-14].
Volume 2, Issue 10, October 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
Figure (2): Image AFM of CdS:In thin films A-without doping B- 1% doping
C- 3% doping D- 5% doping .
3.3 Optical properties
The transmittance of the nano CdS and CdS:In thin films was measured in the wave length range of 300nm to 1100nm.
The films, exhibit good transmittance of about 68% for the undoped CdS, but it decreases with a low doping
concentration (0.1%). The transmittance also increases with increasing the doping ratio (5%), which may be related to
increase in thickness of the doped film. Afterward, it finally decreases, similar to the observation by khallaf [3]. The
decrease in transmittance may be related to the increase nano grain size, shown from the XRD and AFM analyses as
shown in Fig (1) and Table (1). These findings which is agrees with the results of Shadia [4].
The films showed greater transmittance (75%) beyond the absorption edge with the different ratios of In doping. A red
shift in the absorption edge toward lower band gap is noticed in the doped films, as shown in Fig (3)(A) and Table (2).
Figure (3)(B) shows that the absorption edge of the film with higher doping ratio is blue shifts with respect to that of the
films with lower doping ratio, which disagrees withthe report of Shadia [4]. In this study, the absorption edge of the film
may be related to the dominant behavior of the quantum dot nano structure dominant behavior in this study. The value of
the optical energy band gap was estimated from the plots of (αhν)2 versus (hν), as shown in Fig.(3)(C) where α is the
absorption coefficient and ν is the frequency of the radiation. Given that α> 104 cm-1 and the plots are linear, the direct
nature of the optical transition is confirmed. The direct optical energy gap (Eg) decreases from 3.84 eV for the undoped
CdS to 3.64 eV, 3.72 eV and 3.79 eV for the doped CdS by 1%, 3% and 5% In doping, respectively. Table (2). The
higher value of the (Eg) compared with that of the bulk energy gap of 2.42 eV , indicates that the film have a quantum
dote nano structure. Table (2) obtain that (Eg) was slightly larger for the higher doping ratio. The increase in (Eg) is due
to the increase in the carrier doping concentration with doping , and can be attributed to the Moss-Burstein shift [15,16].
The decreases in (Eg) may be due to the replacement of larger number of substitutional or interstitial cadmium ions by
indium ions to increase the grainsize [1].
Volume 2, Issue 10, October 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
ISSN 2319 - 4847
Figure (3): Optical properties of CdS:In thin films a- The spectrum transmittance (T)
b- The optical absorption coefficient(α) c- energy gap (Eg).
Tabe (2).Variation energy gap of CdS and CdS:In thin films with different doping ratio.
4. CONCLUSION
Nano particles of CdS and CdS:In thin films were prepared by CBD method. XRD results show the a polycrystalline
structure of CdS and 0.1% In-doped CdS with hexagonal structure at the (111) preferred plane. By contrast, at 3% and
5% In-doped CdS film, its structure became amorphous. According to XRD analysis. The particle size of CdS according
to XRD is in the range 2nm to 3nm. The AFM micrograph showed that the films were good homogeneous and had a
nanoparticle size of
(36 nm to 67.53nm). Optical studies revealed that CdS or CdS:In thin films have
transmittances that depends on the doping ratio with allow direct transition of the optical band gap, which varies from
3.84 eV for undoped CdS to 3.79 eV for 5% In doped CdS. A high energy gap indicates quantum confinement effects in
the nano-particles. These nanoparticle films are promising candidates for optoelectronic applications.
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Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 10, October 2013
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