SCANNING VOL. 37, 389–392 (2015) © Wiley Periodicals, Inc.
Study of the Morphology of ZnS Thin Films Deposited on Different Substrates Via Chemical Bath Deposition MEZ-GUTIERREZ CLAUDIA M. GO ,1 P.A. LUQUE,1 A. CASTRO-BELTRAN,2 A.R. VILCHIS-NESTOR,3 EDER LUGO-MEDINA,4 5 A. CARRILLO-CASTILLO, M. A. QUEVEDO-LOPEZ,6 AND A. OLIVAS7 1
Facultad de Ingenier,, a, Arquitectura y Dise~no, UABC, Ensenada, B.C., Mexico Facultad de Ingeniera Mochis, UAS, Los Mochis, Sinaloa, Mexico 3 Centro Conjunto de Investigacion en Qumica Sustentable UAEM-UNAM, Toluca, Mexico 4 Departamento de Ingeniera Qumica, IT de Los Mochis, Los Mochis, Sinaloa, Mexico 5 Instituto de Ingeniera y Tecnologa, UACJ, Cd. Juarez, Chihuahua, Mexico 6 Department of Materials Science and Engineering, UT at Dallas, Richardson, Texas 7 Centro de Nanociencias y Nanotecnologa-UNAM, Ensenada, B.C., Mexico 2
Summary: In this work, the influence of substrate on the morphology of ZnS thin films by chemical bath deposition is studied. The materials used were zinc acetate, tri-sodium citrate, thiourea, and ammonium hydroxide/ammonium chloride solution. The growth of ZnS thin films on different substrates showed a large variation on the surface, presenting a poor growth on SiO2 and HfO2 substrates. The thin films on ITO substrate presented a uniform and compact growth without pinholes. The optical properties showed a transmittance of about 85% in the visible range of 300–800 nm with band gap of 3.7 eV. SCANNING 37:389–392, 2015. © 2015 Wiley Periodicals, Inc. Key words: substrate, CBD, ZnS, substrates, thin films
Introduction The ZnS thin films are compound semiconductors with large range of potential applications as they have a large band gap of 3.7 eV in bulk (Kawar and Pawar, 2010). ZnS films are successfully used in solar cells employed as buffer layers, realizing high-efficiency CIGS solar cells, and several types of TFSCs, such as CuInS2, CuInSe2 (CIS), Cu(In,Ga)Se2 (CIGS) (Liu et al., 2014b), because these materials are transparent to
Address for reprints: P.A. Luque, Facultad de Ingeniera, Arquitectura y Dise~no, UABC, C.P. 22860, Ensenada, B.C., Mexico. E-mail: [email protected] Received 22 January 2015; revised 9 May 2015; Accepted with revision 11 May 2015 DOI: 10.1002/sca.21227 Published online 25 May 2015 in Wiley Online Library (wileyonlinelibrary.com).
almost all wavelengths of the solar spectrum (Islam et al., 2009). Also, because of this transparency, they are used as key materials for light-emitting diodes (Nakamura et al., 2000). They are also used the production of commercial thin films phosphors for electro-luminescent (EL) device applications (Dimitrova and Tate, 2000). ZnS thin films have been prepared by various techniques such as: Successive Ionic Layer Adsorption and Reaction (SILAR), which is a distinctive method in which thin films of compound semiconductors are deposited by alternatively dipping a substrate into aqueous solutions containing ions of each component (Ates et al., 2007); Sputtering, a technique for large area films of well-controlled composition and growth rates, controlled through changing the sputtering time, high enough for thick films and low enough for ultrathin films (Daz-Reyes et al., 2015); Atomic Layer Deposition (ALD), based on the self-limiting, sequential reactions between surface adsorbates and gaseous reactants, which allow the precise control of film thickness with a high spatial uniformity and low defect density (Shin and Jin, 2004); and Chemical Bath Deposition (CBD) (Luque et al., 2015; Saeed et al., 2015). Among them, CBD, a technique used for the deposition of semiconductors, is as simple a method of deposition as it is convenient and inexpensive (Barote et al., 2012). The thickness of thin films is controlled by variation of the deposition time and can be performed in atmospheric conditions (Kraini et al., 2013). Also, the CBD method depends on different factors such as complexing agents, precursor concentration, and reaction temperature (Long et al., 2013; Deepa et al., 2014). The CBD method has been successfully used for the deposition of lead sulfide (PbS) (Carrillo-Castillo et al., 2014), cadmium sulfide (CdS) (Ghosh et al., 2014), lanthanum ruthenate (La-Ru-O) (Bencan et al., 2007),
SCANNING VOL. 37, 6 (2015)
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indium sulfide (In2S) (Yahmadi et al., 2005), and bismuth trisulfide (Bi2S3) (Lokhande et al., 2002). In the current work, we report the effect of the substrates on the morphological and optical properties of the ZnS thin films via chemical bath deposited.
water rinse and dried with N2. The ZnS films were characterized using different techniques. The morphology was analyzed in a Zeiss SUPRA 40 SEM with an operating voltage of 15 kV. The optical properties were studied using a Cary 100 UV–Vis spectrophotometer.
Materials and Methods
Results and Discussion
The ZnS thin films were chemically deposited from an aqueous solution prepared from 0.8 mL of tri-sodium citrate, 2.5 mL of zinc acetate, and 2.5 mL of thiourea were utilized as the zinc and the sulfur sources, respectively. The temperature of the solution was kept at 80˚C 1˚C and the reaction time was 90 min. The pH was adjusted to 10.5 adding ammonium hydroxide/ ammonium chloride solution. The substrates used were: soda-lime glass, silicon nitrate (Si3N4), silicon (Si), silicon oxide (SiO2), hafnium oxide (HfO2), and indium tin oxide (ITO). After deposition, the films were cleaned in an ultrasonic bath with methanol followed by distilled
The morphology of zinc sulfide thin films deposited on different substrates was studied by scanning electron microscopy (SEM), as shown in Figure 1. SEM yields microscopic information of the surface. This technique was helpful to identify the growth mode, determining the substrate effect on the films morphology. The ZnS thin films deposited on glass substrate showed a homogeneous and compact growth with some clusters and cracks on the surface. Average ZnS thickness was obtained by measuring a film with SEM cross-section. The resulting thickness value is 60 nm for a deposition time of 90 min. The ZnS films
Fig. 1.
SEM images of ZnS films deposited on different substrates: (a) Glass, (b) HfO2, (c) SiO2, (d) Si3N4, (e) ITO and (f) Si.
G omez-Gutierrez et al.: Study of the Morphology of ZnS Thin Films Via Chemical Bath Deposition
Fig. 2.
Growth system of ZnS thin films via cluster by cluster
presented cluster-by-cluster growths (Fig. 2) where the solution has high concentrations of the source metal (Liuet al., 2014a) presenting some pinholes and clusters on the surface, as shown in Figure 1(a). In this process, the particles are clustered due to a homogeneous reaction where the ZnS is absorbed in bulk and, subsequently, demonstrates semiconductor cluster dissemination towards the substrate (O’Brien and McAleese, ’98). In Figure 1(b) shows that the growth of ZnS thin films on HfO2 substrate, where, the ZnS particles are dispersed throughout the substrate, the morphology of these is spherical trend, showing a width of about 50 nm, this growth is due to the degree of hydrophobicity of the substrate (Su-Shia and Chung-Sheng, 2013), resulting in a heterogeneous film. The results of ZnS films deposited on SiO2 substrate is shown in the Figure 1(c), the growth of ZnS film on SiO2, is a similar to the films deposited on HfO2 substrate, showing many pinholes on the surface and a heterogeneous growth with agglomerated of zinc sulfide particles in certain parts of the substrate, the thickness was about 60 nm, presenting variations in the thickness of the particles. The ZnS thin films on Si3N4 substrate (Figure 1(d)), showed non-uniform growth and some pinholes on the film surface, in this substrate. The thickness of the ZnS thin film deposited
Fig. 3.
391
on Si3N4 substrate was around 30 nm, the ZnS growth on this substrate showed a smaller thickness compared with the other substrates, this may be, due to the interaction of the metal and the sulfur source, where, the reaction rate is slower, resulting in slower growth of ZnS film. The Figure 1(e) shows the growth of ZnS thin films on ITO (Indium tin oxide) substrate, the films showed a uniform and compact growth without the presence of pinholes on the film surface, presenting a cluster by cluster growth, the thickness of the film was about 30 nm. The ZnS thin film on ITO substrate was the more homogeneous and compact of all the substrates. In the Figure 1(f), we can be observed the growth of the ZnS thin film on Si substrate, where the films presented a homogeneous and compact morphology with some very small pinholes, the growth of the ZnS film on Si is very similar to the growth of ZnS on glass. However, the grain size is larger in the silicon substrate than in glass substrate, the thickness of ZnS thin film on Si substrate was about 50 nm. A method for band gap determination of the ZnS film is to study the absorption or transmission spectra of the sample. To do this, ZnS films were grown onto an optically transparent substrate. The absorption measurement at various wavelengths (UV-Vis) of the ZnS film deposited on glass substrate was used to estimate the optical band gap. Transmittance measurements were performed over a spectral ranging between 300 to 800 nm on ZnS thin films deposited on glass substrate and are shown in Figure 3(a). The transmittance of the ZnS thin films were about 85%, this value is very similar to other experiment reported previously (Ke et al., 2014). The values of the energy band gap were calculated with relationship between absorption coefficient (a) the incident phonon energy (ahʋ) can be expresses as follow (Praus et al., 2012), (ahʋ)2 ¼ A(hʋ-Eg), where, Eg, is the optical band gap of the film and A is a constant. The optical band gap can
Optical properties, (a) transmittance spectra and (b) curve of hv-ahv2.
392
SCANNING VOL. 37, 6 (2015)
be calculated by extrapolating the straight linear portion of the plots between (ahʋ)2 and hʋ to the energy axis. The optical bang gap of ZnS thin film was about 3.7 eV, as shown in Figure 3(b), this value are reported by the literature for ZnS thin films (Zhou et al., 2013).
Conclusions Zinc sulfide (ZnS) thin films have been prepared by chemical bath deposition on different substrates in an alkaline solution. The morphology of the surface showed that the films are compact and uniform, with some pinholes on the surface depending of the substrate. The most homogenous surfaces were using the ITO substrate. The transmission spectrum indicates an average transmittance of 85% in the spectra range from 300 nm to 800 nm, and the optical band gap calculated of the films was around 3.7 eV.
Acknowledgments The authors are grateful to A. Salas Villase~nor and E. Flores for their technical assistance, as well as the DGAPA-PAPIIT IN108613-2 project for their support.
References Ates A,Yıldırım M, Kundakcı M, Astam A. 2007. Annealing and light effect on optical and electrical properties of ZnS thin films grown with the SILAR method. Mater Sci Semicond Process 10:281–286. Barote MA, Kamble SS, Yadav AA, Masumdar EU. 2012. Optical and electrical characterization of chemical bath deposited Cd-Pb-S thin films. Thin Solid Films 526:97–102. Bencan A, Malic B, Drazic G, Vukadinovic M, Kosec M. 2007. Characterization of lead zirconate titanate—lanthanum ruthenate thin film structures prepared by chemical solution deposition. Scanning 29:287–293. Carrillo-Castillo A, Ambrosio Lazaro RC, Jimenez-Perez A, et al. 2014. Role of complexing agents in chemical bath deposition of lead sulfide thin films. Mater Lett 121:19–21. Deepa K, Preetha KC, Murali KV, et al. 2014. The effect of various complexing agents on the morphology and optoelectronic properties of chemically deposited ZnS thin films: A comparative study. Optik 125:5727–5732. Daz-Reyes J, Castillo-Ojeda RS, Sanchez-Espndola R, GalvanArellano M, Zaca-Moran O. 2015. Structural and optical characterization of wurtzite type ZnS. Curr Appl Phys 15:103–109. Dimitrova V, Tate J. 2000. Synthesis and characterization of some ZnS-based thin Films phosphors for electroluminescent device applications. Thin Solid Films 365:134–138.
Ghosh B, Kumar K, Singh B, Banerjee P, Das S. 2014. Growth of CdS thin films on indium coated glass substrates via chemical bath deposition and subsequent air annealing. Appl Surf Sci 320:309–314. Islam MM, Ishizuka S, Yamada A, et al. 2009. CIGS solar cell with MBE-grown ZnS buffer layer. Sol Energ Mat Sol C 93:970–972. Kawar SS, Pawar BH. 2010. Nanocrystalline grain size in ZnS thin films deposited by chemical bath technique. J Mater Sci Mater Electron 21:906–909. Ke H, Duo S, Liu T, Sun Q, Ruan C, Fei X, Tan J, Zhan S. 2014. Effect of temperature on structural and optical properties of ZnS thin films by chemical bath deposition without stirring the reaction bath. Mater Sci Semicond Process 18:28–35. Kraini M, Bouguila N, Halidou I, Timoumi A, Alaya S. 2013. Properties of In2O3 films obtained by thermal oxidation of sprayed In2S3. Mater Sci Semicond Process 16: 1388–1396. Liu J, Wei A, Zhao Y. 2014a. Effect of different complexing agents on the properties of chemical-bath-deposited ZnS thin films. J Alloys Compd 588:228–234. Liu T, Ke H, Zhang H, et al. 2014b. Effect of four different zinc salts and annealing treatment on growth, structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition. Mater Sci Semicond Process 26:301–311. Lokhande CD, Sankapal BR, Mane RS, et al. 2002. Structural characterization of chemically deposited Bi2S3 and Bi2Se3 thin films. Appl Surf Sci 187:108–115. Long W, Siao C, Huei S, Jauh W, Lon C. 2013. Effect of deposition variables on properties of CBD ZnS thin films prepared in chemical bath of ZnSO4/SC(NH2)2/Na3C3H5O7/ NH4OH. Appl Surf Sci 264:213–218. Luque PA, Castro-Beltran A, Vilchis-Nestor AR, Quevedo-Lopez MA, Olivas A. 2015. Influence of pH on properties of ZnS thin films deposited on SiO2 substrate by chemical bath deposition. Mater Lett 140:148–150. Nakamura S, Yamada Y, Taguchi T. 2000. Room-temperature 340nm ultraviolet electroluminescence from ZnS-based lightemitting diodes. J Cryst Growth 214:1091–1095. O’Brien P, McAleese J. 1998. Developing an understanding of the processes controlling the chemical bath deposition of ZnS and CdS. J Mater Chem 8:2309–2314. Praus P, Dvorsky R, Horn-kova P, Pospsil M, Kovar P. 2012. Precipitation, stabilization and molecular modeling of ZnS nanoparticles in the presence of cetyltrimethylammonium bromide. J Colloid Interface Sci 377:58–63. Saeed M, Azad M, Riaz S, Naseem S, O’Brien P. 2015. Optimising conditions for the growth of nanocrystalline ZnS thin films from acidic chemical baths. Mater Sci Semicond Process 30:292–297. Shin Y, Jin S. 2004. Studies on polycrystalline ZnS thin films grown by atomic layer deposition for electroluminescent applications. Appl Surf Sci 229:105–111. Su-Shia L, Chung-Sheng L. 2013. The hydrophobicity and optical properties of the HfO2-deposited glass. Ceram Int 39: 353–358. Yahmadi B, Kamoun N, Bennaceur R, et al. 2005. Structural analysis of indium sulphide thin films elaborated by chemical bath deposition. Thin Solid Films 473:201–207. Zhou L, Tang N, Wu S. 2013. Influence of deposition temperature on ZnS thin film performance with chemical bath deposition. Surf Coat Tech 228:S146–S149.
Study of the Morphology of ZnS Thin Films Deposited on Different Substrates Via Chemical Bath Deposition MEZ-GUTIERREZ CLAUDIA M. GO ,1 P.A. LUQUE,1 A. CASTRO-BELTRAN,2 A.R. VILCHIS-NESTOR,3 EDER LUGO-MEDINA,4 5 A. CARRILLO-CASTILLO, M. A. QUEVEDO-LOPEZ,6 AND A. OLIVAS7 1
Facultad de Ingenier,, a, Arquitectura y Dise~no, UABC, Ensenada, B.C., Mexico Facultad de Ingeniera Mochis, UAS, Los Mochis, Sinaloa, Mexico 3 Centro Conjunto de Investigacion en Qumica Sustentable UAEM-UNAM, Toluca, Mexico 4 Departamento de Ingeniera Qumica, IT de Los Mochis, Los Mochis, Sinaloa, Mexico 5 Instituto de Ingeniera y Tecnologa, UACJ, Cd. Juarez, Chihuahua, Mexico 6 Department of Materials Science and Engineering, UT at Dallas, Richardson, Texas 7 Centro de Nanociencias y Nanotecnologa-UNAM, Ensenada, B.C., Mexico 2
Summary: In this work, the influence of substrate on the morphology of ZnS thin films by chemical bath deposition is studied. The materials used were zinc acetate, tri-sodium citrate, thiourea, and ammonium hydroxide/ammonium chloride solution. The growth of ZnS thin films on different substrates showed a large variation on the surface, presenting a poor growth on SiO2 and HfO2 substrates. The thin films on ITO substrate presented a uniform and compact growth without pinholes. The optical properties showed a transmittance of about 85% in the visible range of 300–800 nm with band gap of 3.7 eV. SCANNING 37:389–392, 2015. © 2015 Wiley Periodicals, Inc. Key words: substrate, CBD, ZnS, substrates, thin films
Introduction The ZnS thin films are compound semiconductors with large range of potential applications as they have a large band gap of 3.7 eV in bulk (Kawar and Pawar, 2010). ZnS films are successfully used in solar cells employed as buffer layers, realizing high-efficiency CIGS solar cells, and several types of TFSCs, such as CuInS2, CuInSe2 (CIS), Cu(In,Ga)Se2 (CIGS) (Liu et al., 2014b), because these materials are transparent to
Address for reprints: P.A. Luque, Facultad de Ingeniera, Arquitectura y Dise~no, UABC, C.P. 22860, Ensenada, B.C., Mexico. E-mail: [email protected] Received 22 January 2015; revised 9 May 2015; Accepted with revision 11 May 2015 DOI: 10.1002/sca.21227 Published online 25 May 2015 in Wiley Online Library (wileyonlinelibrary.com).
almost all wavelengths of the solar spectrum (Islam et al., 2009). Also, because of this transparency, they are used as key materials for light-emitting diodes (Nakamura et al., 2000). They are also used the production of commercial thin films phosphors for electro-luminescent (EL) device applications (Dimitrova and Tate, 2000). ZnS thin films have been prepared by various techniques such as: Successive Ionic Layer Adsorption and Reaction (SILAR), which is a distinctive method in which thin films of compound semiconductors are deposited by alternatively dipping a substrate into aqueous solutions containing ions of each component (Ates et al., 2007); Sputtering, a technique for large area films of well-controlled composition and growth rates, controlled through changing the sputtering time, high enough for thick films and low enough for ultrathin films (Daz-Reyes et al., 2015); Atomic Layer Deposition (ALD), based on the self-limiting, sequential reactions between surface adsorbates and gaseous reactants, which allow the precise control of film thickness with a high spatial uniformity and low defect density (Shin and Jin, 2004); and Chemical Bath Deposition (CBD) (Luque et al., 2015; Saeed et al., 2015). Among them, CBD, a technique used for the deposition of semiconductors, is as simple a method of deposition as it is convenient and inexpensive (Barote et al., 2012). The thickness of thin films is controlled by variation of the deposition time and can be performed in atmospheric conditions (Kraini et al., 2013). Also, the CBD method depends on different factors such as complexing agents, precursor concentration, and reaction temperature (Long et al., 2013; Deepa et al., 2014). The CBD method has been successfully used for the deposition of lead sulfide (PbS) (Carrillo-Castillo et al., 2014), cadmium sulfide (CdS) (Ghosh et al., 2014), lanthanum ruthenate (La-Ru-O) (Bencan et al., 2007),
SCANNING VOL. 37, 6 (2015)
390
indium sulfide (In2S) (Yahmadi et al., 2005), and bismuth trisulfide (Bi2S3) (Lokhande et al., 2002). In the current work, we report the effect of the substrates on the morphological and optical properties of the ZnS thin films via chemical bath deposited.
water rinse and dried with N2. The ZnS films were characterized using different techniques. The morphology was analyzed in a Zeiss SUPRA 40 SEM with an operating voltage of 15 kV. The optical properties were studied using a Cary 100 UV–Vis spectrophotometer.
Materials and Methods
Results and Discussion
The ZnS thin films were chemically deposited from an aqueous solution prepared from 0.8 mL of tri-sodium citrate, 2.5 mL of zinc acetate, and 2.5 mL of thiourea were utilized as the zinc and the sulfur sources, respectively. The temperature of the solution was kept at 80˚C 1˚C and the reaction time was 90 min. The pH was adjusted to 10.5 adding ammonium hydroxide/ ammonium chloride solution. The substrates used were: soda-lime glass, silicon nitrate (Si3N4), silicon (Si), silicon oxide (SiO2), hafnium oxide (HfO2), and indium tin oxide (ITO). After deposition, the films were cleaned in an ultrasonic bath with methanol followed by distilled
The morphology of zinc sulfide thin films deposited on different substrates was studied by scanning electron microscopy (SEM), as shown in Figure 1. SEM yields microscopic information of the surface. This technique was helpful to identify the growth mode, determining the substrate effect on the films morphology. The ZnS thin films deposited on glass substrate showed a homogeneous and compact growth with some clusters and cracks on the surface. Average ZnS thickness was obtained by measuring a film with SEM cross-section. The resulting thickness value is 60 nm for a deposition time of 90 min. The ZnS films
Fig. 1.
SEM images of ZnS films deposited on different substrates: (a) Glass, (b) HfO2, (c) SiO2, (d) Si3N4, (e) ITO and (f) Si.
G omez-Gutierrez et al.: Study of the Morphology of ZnS Thin Films Via Chemical Bath Deposition
Fig. 2.
Growth system of ZnS thin films via cluster by cluster
presented cluster-by-cluster growths (Fig. 2) where the solution has high concentrations of the source metal (Liuet al., 2014a) presenting some pinholes and clusters on the surface, as shown in Figure 1(a). In this process, the particles are clustered due to a homogeneous reaction where the ZnS is absorbed in bulk and, subsequently, demonstrates semiconductor cluster dissemination towards the substrate (O’Brien and McAleese, ’98). In Figure 1(b) shows that the growth of ZnS thin films on HfO2 substrate, where, the ZnS particles are dispersed throughout the substrate, the morphology of these is spherical trend, showing a width of about 50 nm, this growth is due to the degree of hydrophobicity of the substrate (Su-Shia and Chung-Sheng, 2013), resulting in a heterogeneous film. The results of ZnS films deposited on SiO2 substrate is shown in the Figure 1(c), the growth of ZnS film on SiO2, is a similar to the films deposited on HfO2 substrate, showing many pinholes on the surface and a heterogeneous growth with agglomerated of zinc sulfide particles in certain parts of the substrate, the thickness was about 60 nm, presenting variations in the thickness of the particles. The ZnS thin films on Si3N4 substrate (Figure 1(d)), showed non-uniform growth and some pinholes on the film surface, in this substrate. The thickness of the ZnS thin film deposited
Fig. 3.
391
on Si3N4 substrate was around 30 nm, the ZnS growth on this substrate showed a smaller thickness compared with the other substrates, this may be, due to the interaction of the metal and the sulfur source, where, the reaction rate is slower, resulting in slower growth of ZnS film. The Figure 1(e) shows the growth of ZnS thin films on ITO (Indium tin oxide) substrate, the films showed a uniform and compact growth without the presence of pinholes on the film surface, presenting a cluster by cluster growth, the thickness of the film was about 30 nm. The ZnS thin film on ITO substrate was the more homogeneous and compact of all the substrates. In the Figure 1(f), we can be observed the growth of the ZnS thin film on Si substrate, where the films presented a homogeneous and compact morphology with some very small pinholes, the growth of the ZnS film on Si is very similar to the growth of ZnS on glass. However, the grain size is larger in the silicon substrate than in glass substrate, the thickness of ZnS thin film on Si substrate was about 50 nm. A method for band gap determination of the ZnS film is to study the absorption or transmission spectra of the sample. To do this, ZnS films were grown onto an optically transparent substrate. The absorption measurement at various wavelengths (UV-Vis) of the ZnS film deposited on glass substrate was used to estimate the optical band gap. Transmittance measurements were performed over a spectral ranging between 300 to 800 nm on ZnS thin films deposited on glass substrate and are shown in Figure 3(a). The transmittance of the ZnS thin films were about 85%, this value is very similar to other experiment reported previously (Ke et al., 2014). The values of the energy band gap were calculated with relationship between absorption coefficient (a) the incident phonon energy (ahʋ) can be expresses as follow (Praus et al., 2012), (ahʋ)2 ¼ A(hʋ-Eg), where, Eg, is the optical band gap of the film and A is a constant. The optical band gap can
Optical properties, (a) transmittance spectra and (b) curve of hv-ahv2.
392
SCANNING VOL. 37, 6 (2015)
be calculated by extrapolating the straight linear portion of the plots between (ahʋ)2 and hʋ to the energy axis. The optical bang gap of ZnS thin film was about 3.7 eV, as shown in Figure 3(b), this value are reported by the literature for ZnS thin films (Zhou et al., 2013).
Conclusions Zinc sulfide (ZnS) thin films have been prepared by chemical bath deposition on different substrates in an alkaline solution. The morphology of the surface showed that the films are compact and uniform, with some pinholes on the surface depending of the substrate. The most homogenous surfaces were using the ITO substrate. The transmission spectrum indicates an average transmittance of 85% in the spectra range from 300 nm to 800 nm, and the optical band gap calculated of the films was around 3.7 eV.
Acknowledgments The authors are grateful to A. Salas Villase~nor and E. Flores for their technical assistance, as well as the DGAPA-PAPIIT IN108613-2 project for their support.
References Ates A,Yıldırım M, Kundakcı M, Astam A. 2007. Annealing and light effect on optical and electrical properties of ZnS thin films grown with the SILAR method. Mater Sci Semicond Process 10:281–286. Barote MA, Kamble SS, Yadav AA, Masumdar EU. 2012. Optical and electrical characterization of chemical bath deposited Cd-Pb-S thin films. Thin Solid Films 526:97–102. Bencan A, Malic B, Drazic G, Vukadinovic M, Kosec M. 2007. Characterization of lead zirconate titanate—lanthanum ruthenate thin film structures prepared by chemical solution deposition. Scanning 29:287–293. Carrillo-Castillo A, Ambrosio Lazaro RC, Jimenez-Perez A, et al. 2014. Role of complexing agents in chemical bath deposition of lead sulfide thin films. Mater Lett 121:19–21. Deepa K, Preetha KC, Murali KV, et al. 2014. The effect of various complexing agents on the morphology and optoelectronic properties of chemically deposited ZnS thin films: A comparative study. Optik 125:5727–5732. Daz-Reyes J, Castillo-Ojeda RS, Sanchez-Espndola R, GalvanArellano M, Zaca-Moran O. 2015. Structural and optical characterization of wurtzite type ZnS. Curr Appl Phys 15:103–109. Dimitrova V, Tate J. 2000. Synthesis and characterization of some ZnS-based thin Films phosphors for electroluminescent device applications. Thin Solid Films 365:134–138.
Ghosh B, Kumar K, Singh B, Banerjee P, Das S. 2014. Growth of CdS thin films on indium coated glass substrates via chemical bath deposition and subsequent air annealing. Appl Surf Sci 320:309–314. Islam MM, Ishizuka S, Yamada A, et al. 2009. CIGS solar cell with MBE-grown ZnS buffer layer. Sol Energ Mat Sol C 93:970–972. Kawar SS, Pawar BH. 2010. Nanocrystalline grain size in ZnS thin films deposited by chemical bath technique. J Mater Sci Mater Electron 21:906–909. Ke H, Duo S, Liu T, Sun Q, Ruan C, Fei X, Tan J, Zhan S. 2014. Effect of temperature on structural and optical properties of ZnS thin films by chemical bath deposition without stirring the reaction bath. Mater Sci Semicond Process 18:28–35. Kraini M, Bouguila N, Halidou I, Timoumi A, Alaya S. 2013. Properties of In2O3 films obtained by thermal oxidation of sprayed In2S3. Mater Sci Semicond Process 16: 1388–1396. Liu J, Wei A, Zhao Y. 2014a. Effect of different complexing agents on the properties of chemical-bath-deposited ZnS thin films. J Alloys Compd 588:228–234. Liu T, Ke H, Zhang H, et al. 2014b. Effect of four different zinc salts and annealing treatment on growth, structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition. Mater Sci Semicond Process 26:301–311. Lokhande CD, Sankapal BR, Mane RS, et al. 2002. Structural characterization of chemically deposited Bi2S3 and Bi2Se3 thin films. Appl Surf Sci 187:108–115. Long W, Siao C, Huei S, Jauh W, Lon C. 2013. Effect of deposition variables on properties of CBD ZnS thin films prepared in chemical bath of ZnSO4/SC(NH2)2/Na3C3H5O7/ NH4OH. Appl Surf Sci 264:213–218. Luque PA, Castro-Beltran A, Vilchis-Nestor AR, Quevedo-Lopez MA, Olivas A. 2015. Influence of pH on properties of ZnS thin films deposited on SiO2 substrate by chemical bath deposition. Mater Lett 140:148–150. Nakamura S, Yamada Y, Taguchi T. 2000. Room-temperature 340nm ultraviolet electroluminescence from ZnS-based lightemitting diodes. J Cryst Growth 214:1091–1095. O’Brien P, McAleese J. 1998. Developing an understanding of the processes controlling the chemical bath deposition of ZnS and CdS. J Mater Chem 8:2309–2314. Praus P, Dvorsky R, Horn-kova P, Pospsil M, Kovar P. 2012. Precipitation, stabilization and molecular modeling of ZnS nanoparticles in the presence of cetyltrimethylammonium bromide. J Colloid Interface Sci 377:58–63. Saeed M, Azad M, Riaz S, Naseem S, O’Brien P. 2015. Optimising conditions for the growth of nanocrystalline ZnS thin films from acidic chemical baths. Mater Sci Semicond Process 30:292–297. Shin Y, Jin S. 2004. Studies on polycrystalline ZnS thin films grown by atomic layer deposition for electroluminescent applications. Appl Surf Sci 229:105–111. Su-Shia L, Chung-Sheng L. 2013. The hydrophobicity and optical properties of the HfO2-deposited glass. Ceram Int 39: 353–358. Yahmadi B, Kamoun N, Bennaceur R, et al. 2005. Structural analysis of indium sulphide thin films elaborated by chemical bath deposition. Thin Solid Films 473:201–207. Zhou L, Tang N, Wu S. 2013. Influence of deposition temperature on ZnS thin film performance with chemical bath deposition. Surf Coat Tech 228:S146–S149.
