Optoelectronic Characterization of Chemical Bath Deposited Cd_xCo_1-xS Thin Film

Chinedu E. Ekuma, Mishark N. Nnabuchi, Eziaku Osarolube, Ephraim O. Chukwuocha, Michael C. Onyeaju

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DOI: 10.4236/jmp.2011.29119                

Abstract

Cadmium Cobalt Sulphide (Cd_xCo_1-xS) thin film was deposited on microscopic glass substrate using chemical bath deposition technique at room temperature from aqueous solutions of Cadmium Chloride, Cobalt Chloride and Thiourea in which ammonium solution was used as complexing agents. The optical properties were characterized using the absorbance and transmission measurement from Unico UV-2102 PC spectrophotometer, at normal incidence of light in the wavelength range of 200 - 1000 nm. We report the deposition and optimization of the growth parameter with respect to time which showed that the band gap energy and the composition verified from the extended Vegard’s law are highly dependent on deposition time. The average transmittance of the film in VIS-NIR region ranges between 30% and 78% with absorbance range of 0.15 - 0.47 within the same wavelength range. The film was also observed to exhibit poor reflectance (11 < R% < 20) which declined albeit exponential within the entire studied wavelength range. From absorbance and transmittance spectra, the band gap energy determined for the film deposited at various time: 19 h, 21 h and 24 h are 2.25 eV, 2.17 eV and 2.05 eV respectively, in that order. The composition of the ternary system for 19 h; 21 h, and 24 h were found to be (x = 0.75; 0.83 and 0.94), respectively. Other optical and dielectric properties of the films were also characterized. Based on the exhibited properties of the film, it can be concluded that it is a promising material for selective coatings for solar cells; effective coatings for poultry houses; use as antireflective coating materials, and for fabrication of optoelectronic devices.

Keywords

Cd_xCo_1-xS, CVD, Thin Films, Band Gap, Vegard’s Law

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	T. Yamaguchi, Y. Yamamoto, T. Tanaka, Y. Demizu and A. Yoshida, “(Cd,Zn)S Thin Films Prepared by Chemical Bath Deposition for Photovoltaic Devices,” Thin Solid Films, Vol. 281-282, 1996, pp. 375-378.
[2]	E. Bacaksiz, M. Tomakin, M. Attunbas, M. Parlac and T. Colakoglu, “Structural, Optical and Magnetic Properties of Cd1?xCoxS Thin Films Prepared by Spray Pyrolysis,” Physica B: Condensed Matter, Vol. 403, No. 19-20, 2008, pp. 3740-3745. doi:10.1016/j.physb.2008.07.006
[3]	T. L. Chu, S. S. Chu, J. Britt, C. Ferrikide and O. Q. Wu, “Cadmium Zinc Sulfide Films and Heterojunctions,” Journal of Applied Physics, Vol. 70, No. 5, 1991, pp. 2688-2693. doi:10.1063/1.349384
[4]	F. I. Ezema, “Optical Characterization of Chemical Bath Deposited Bismuth Oxyiodide (BiOI) Thin Films,” Tur-kish Journal of Physics, Vol. 29, No. 2, 2005, p. 105-114.
[5]	R. S. Mane and C. D. lokhande, “Chemical Deposition Method for Metal Chalcogenide Thin Films,” Material Chemistry and Physics, Vol. 65, No. 1, 2002, pp. 1-31. doi:10.1016/S0254-0584(00)00217-0
[6]	R. Poulomi, and S. Kumar, “Chemical Bath Deposition of MoS2 Thin Film Using Ammonium Tetrathiomolybdate as a Single Source for Molybdenum and Sulphur,” Thin Solid Films, Vol. 496, No. 2, 2006, pp. 293-298. doi:10.1016/j.tsf.2005.08.368
[7]	C. A. Estrada, P. K. Nair, M. T. S. Nair, R. A. Zingaro and E. A. Meyers, “Chemical Bath Deposition of ZnSe and CuSe Thin Films Using N,N-Dimethylselenourea,” Journal of Electrochemical Society, Vol. 141, No. 3, 1994, pp. 802-806. doi:10.1149/1.2054814
[8]	D. S. Boyle, O. Robbe, D. P. Halliday, M. R. Heinreich, A. Bayer, O. Brien, P. D. J. Otway and M. D. G. Potter, “A Novel Method for the Synthesis of the Ternarythin Film Semiconductor Cadmium Zinc Sulfide from Acidic Chemical Baths,” Journal of Materials Chemistry, Vol. 10, 2000, pp. 2439-2441. doi:10.1039/b005544l
[9]	G. Hodes, “Chemical Solution Deposition of Semicon-ductor Films,” CRC Press, New York, 2000.
[10]	J. Zhou, X. Wu, GTeeter, B. To, Y. Yan, R. G. Dhere and T. A. Gessert, “CBD-Cd1?xZnxS Thin Films and Their Application in CdTe Solar Cells,” Physica Status Solidi, Vol. 241, No. 3, 2004, pp. 775-778. doi:10.1002/pssb.200304218
[11]	I. O. Oladeji, L. Chow, C. Ferekides, V. Viswanathan and Z. Zhao, “Metal/CdTe/CdS/Cd1?xZnxS/TCO/Glass: A New CdTe Thin Film Solar Cell Structure,” Solar Energy Materials & Solar Cells, Vol. 61, No. 2, 2000, pp. 203-211. doi:10.1016/S0927-0248(99)00114-2
[12]	J. Singh, “Optical Properties of Condensed Matter and Applications,” John Wiley & Sons, Hoboken, 2006.
[13]	K. Shimakawa, “On the Compositional Dependence of the Optical Gap in Amorphous Semiconducting Alloys,” Journal of Non-Crystalline Solids, Vol. 43, 1981, p. 229-244. doi:10.1016/0022-3093(81)90119-8
[14]	J. C. Phillips, “Bond and Band in Semiconductors,” Aca-demic Press, New York, 1973.
[15]	K. Osamura, S. Naka and Y Murakami, “Preparation and Optical Properties of Ga1?xInxN Thin Films,” Journal of Applied Physics, Vol. 46, 1975, p. 3432-3438. doi:10.1063/1.322064
[16]	K. Yen-Kuang, C. Han-Yi, Y. Sheng-Horng, L. Bo-Ting and C. Mei-Ling, “Bowing Parameter of Zincblende Inx-Ga1?xN,” Optics Communication, Vol. 280, No. 1, 2007, pp. 153-156. doi:10.1016/j.optcom.2007.07.058
[17]	M. C. Tamargo, “Optical Properties of Electronic Structure of Semiconductors,” In: C. Hernandez, Ed., II – VI Semiconductor Materials and Their Application, Taylor and Francis, New York, 2002, pp. 113-170.