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Optostructural and electrical studies on electrodeposited Indium doped ZrS2 thin films
Journal of Alloys and Compounds 474 (2009) 14–17
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Optostructural and electrical studies on electrodeposited Indium doped ZrS2 thin films A.M. Sargar, N.S. Patil, S.R. Mane, S.N. Gawale, P.N. Bhosale ∗ Materials Research Laboratory, Department of Chemistry, Shivaji University, Kolhapur 416004, India
a r t i c l e
i n f o
Article history: Received 28 May 2008 Received in revised form 12 June 2008 Accepted 14 June 2008 Available online 8 August 2008 Keywords: Thin films Chemical synthesis Optical properties X-ray diffraction
a b s t r a c t Electrochemical deposition and characterization of indium doped zirconium disulphide (In:ZrS2 ) thin films deposited onto stainless steel and fluorine doped tin oxide (FTO) coated conducting glass plates from an aqueous bath containing ZrO(NO3 )2 , Na2 S2 O3 ·5H2 O and In2 (SO4 )3 is discussed in present manuscript. The prepared films were characterized by X-ray diffraction analysis (XRD), energy dispersive X-ray analysis (EDS), scanning electron microscopy (SEM) and optical absorption techniques. The structure was found to be hexagonal with preferential orientation along (1 0 2) plane. SEM study shows that the total substrate surface is well covered by densely packed spherical shaped grains. Optical absorption study shows the presence of direct transition having band gap energy 1.78 eV. In:ZrS2 is n-type semiconductor having activation energy, 0.033 eV in low temperature region and 0.106 eV in high temperature region. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Semiconducting thin film materials which is based on sulphide, selenides and tellurides, have attracted much attention for fabrication of solar cells and optoelectronic technology [1]. One of the main challenge in solar energy research is to find and fabricate the method that yield high quality thin films at low cost and easily scalable. The high quality thin films can be usually obtained by vaccum deposition, chemical bath deposition and electrodeposition [2–6]. Electrodeposition, also known as electrochemical deposition, or electrocrystallization, is one of the most useful technique for preparing thin films on the surface of conducting substrates [7,8]. An electrochemical technique has numerous advantages including low temperature processing, arbitrary substrate shapes, controllable film thickness, morphology and potential low capital cost. Thin films of ZrSe3 , [9] optical transmission in ZrS3−x Sex single crystals was reported by Provencher et al. [10]. Studies on thermorefelctance spectra of ZrS3−x Sex single crystal [11,12] lithium intercalation in LiX ZrS2 [13] and the fundamental absorption edge in NiX ZrS2 [14] is found in literature. To the best of our knowledge, no report is available for In doped ZrS2 thin film. In the present manuscript, we report, for the first time, the synthesis of Indium doped ZrS2 thin films by electrodeposition technique. Deposition was carried out by using zirconyl nitrate as
∗ Corresponding author. Tel.: +91 231 2609338; fax: +91 231 2691533, 2690333. E-mail address: p n [email protected] (P.N. Bhosale). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.06.077
source of zirconium ions, sodium thiosulphate as source of sulphur ions, and indium sulphate as indium ion source. The influence of growth conditions such as deposition potential, concentration of the constituents of the bath was studied in the initial stage. In order to characterize In doped ZrS2 thin films for their structural, compositional and optical properties; X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), and optical absorption techniques were employed.
2. Experimental In doped ZrS2 thin films were prepared by electrodeposition technique using aqueous solutions of 0.2 M ZrO(NO3 )2 , 0.1 M Na2 S2 O3 ·5H2 O and 0.1 M In2 (SO4 )3 . pH of the electrolytic bath was maintained at 1.9. Stainless steel and Fluorine doped tin oxide (SnO2 ) covered conducting glass plates of resistance 10 cm−1 were used as substrate support in this deposition. These conducting glasses of approximately 1 cm2 area were cleaned with detergent, dried and degreased with acetone and distilled water. The chemicals used in this deposition were of analytical grade. The electrochemical experiments were performed using Princeton PerkinElmer, Applied Research Verrsatat-II; Model 250/270 employing three electrode configurations, with stainless steel and tin oxide coated conducting glass substrate as cathode, graphite plate as anode and saturated calomel electrode (SCE) as reference electrode. Optical absorption was carried out in the range 350–850 nm with Hitachi-330 UV–vis-NIR spectrophotometer. Structure of the films was analyzed by X-ray diffractometer PW-1710 using Cu K␣ radiation ( = 1.5405 Å). Surface morphology and composition of the In doped ZrS2 thin film was studied by using scanning electron microscopy (JEOL JSM-6360) attached with an energy dispersive X-ray analyzer ((EDS). Electrical conductivity measurements in the range of 300–500 K as a function of temperature were performed on In doped ZrS2 thin films using two probe method. The measurement of thermoelectric power was done in the temperature range 300–500 K. For the electrical conductivity and TEP measurement silver contacts were made on the defined area of the film.
A.M. Sargar et al. / Journal of Alloys and Compounds 474 (2009) 14–17
15
Fig. 1. Cyclic voltammogram on stainless-steel substrate in the solution containing (a) 0.2 M ZrO(NO3 )2 ; (b) 0.1M Na2 S2 O3 ·5H2 O; (c) 0.1 M In2 (So4 )3 and (d) 0.2 M ZrO(NO3 )2 + 0.1 M Na2 S2 O3 ·5H2 O + 0.1 M In2 (So4 )3 .
3. Results and discussion 3.1. Cyclic voltammetry studies Preliminary investigations were carried out by cyclic voltammetric studies on deposition of In doped ZrS2 thin films. To optimise the conditions for deposition of Zr, In and S in an aqueous acidic medium, cyclic voltammogram of 0.2 M ZrO(NO3 )2 on stainless steel substrate is recorded and shown in Fig. 1a. It indicates, current start increasing and a cathodic peak is observed at about −0.960 V/SCE, this cathodic current flow is in association with zirconium(IV) reduction process. Fig. 1b shows cyclic voltammogram of 0.1 M Na2 S2 O3 ·5H2 O, reduction at about −0.63 V/SCE may be associated with reduction of thiosulphate ions. This reduction wave may be due to the S2 O3 2− ions released during the disproportionation of Na2 S2 O3 ·5H2 O [15]. Fig. 1c indicates a cyclic voltommogram of 0.1 M In2 (SO4 )3, reduction of elemental indium (In) occurs at a constant potential of −0.43 V/SCE. From the equilibrium electrode potentials of Zr, In and S, it can be seen that equilibrium electrode potential for the deposition of sulphur and indium is positive than that of zirconium deposition. Further, for simultaneous co-deposition of Zr, In and S, the respective electrolyte concentration should be adjusted high or low so as to bring the electrode potentials of all the deposits as closer as possible. Therefore, it is theoretically recommended to use a high concentration of Zr and low concentration for In and S, as deposition potential gets shifted to a negative value. Hence the deposition of In and S will become diffusition controlled due to the low concentration of indium sulphate and sodium thiosulphate. The cyclic voltammogram measured for the electrolytic bath of 0.2 M ZrO(NO3 )2 + 0.1 M Na2 S2 O3 ·5H2 O + 0.1 M In2 (SO4 )3 is shown in Fig. 1d, the reduction potential of −0.850 V/SCE was found to be optimum for the uniform and well adherent In:ZrS2 thin films.
where Eg is the band gap, ˛ the absorption coefficient, the frequency, A is the constant and n can take values 1/2, 3/2, 2 and 3 depending on the mode of transition. Here n = 1/2 offers the best fit for the optical absorption data of In:ZrS2 thin films. The plot of (˛h)2 versus h shown in Fig. 2 is almost linear at higher wavelength and the optical absorption coefficient is of the order of 105 cm−1 supporting the allowed direct band transition of the material. The band gap is determined near the absorption edge by extrapolating the straight portion of the plot to the energy axis and direct band gap energy value was found to be 1.78 eV. 3.3. X-ray diffraction studies Fig. 3 shows XRD pattern of the electrodeposited In:ZrS2 thin film prepared at −0.85 V for the deposition time of 30 min. There are no standard JCPDS data available for Indium doped zirconium disulphide. Hence the plane indices are obtained from comparison between observed ‘d’ values and standard ‘d’ values for ZrS2 and In2 S3 which are given by JCPDS file nos. 11-0679 and 33-0623. It is observed that, the XRD pattern consists of peaks corresponding hexagonal crystallographic planes. From the XRD analysis it is observed that, no separate phase formation of In2 S3 was observed in In:ZrS2 thin films. Table 1 lists the comparison between observed ‘d’ and standard ‘d’ values for In doped ZrS2 thin films. The crystallite size (grain diameter) ‘D’ of the deposits was calculated from the
3.2. Optical absorption studies The room temperature optical absorption was measured for the as-grown In:ZrS2 thin films in the wavelength region of 350–850 nm. The optical absorption coefficient (˛) of In:ZrS2 thin film was calculated using the absorbance value measured for a particular wavelength () and film thickness (t) using the equation: ˛h = A(h − Eg )
n
Fig. 2. Plot of (˛h)2 vs. h for In:ZrS2 thin film deposited at room temperature.
16
A.M. Sargar et al. / Journal of Alloys and Compounds 474 (2009) 14–17
Fig. 3. XRD pattern of as deposited In:ZrS2 thin film at room temperature. Table 1 Comparison of observed ‘d’ values with standard ‘d’ values for In doped ZrS2 thin films Serial number
Observed ‘d’ value (Å)
Standard ‘d’ value (Å)
(h k l) planes
1 2 3 4 5
2.126 1.826 1.452 1.311 1.167
2.14 1.828 1.456 1.332 1.165
102 110 004 113 005
full-width at half-maximum (FWHM) for more intense peak (1 0 2) is 24 nm using the Scherrer formula [16]. 3.4. SEM/EDS studies Fig. 4 shows the scanning electron micrograph of the In:ZrS2 thin film. Densely packed spherical grains are mixed with clusters, which mean that some of the grains are not well developed. The micrograph also reveals that, the material shows compact, large number of spherical grains distributed over the entire surface of the substrate. To analyse atomic percentage of In:ZrS2 thin film EDS technique was used and Fig. 5 shows the EDS pattern of In doped ZrS2 thin
Fig. 4. SEM image of as deposited In:ZrS2 thin film at room temperature.
Fig. 5. EDS analysis of as deposited In:ZrS2 thin film on stainless-steel substrate.
film. The EDS spectrum shows the presence of Zr, In, and S in the film. The atomic percentage for Zr, S and In obtained from the EDS analysis is 36.10, 62.08 and 01.82 respectively. 3.5. Electrical/TEP studies Electrical behaviour was studied by using two-point probe technique, varying the temperature range 300–500 K, under constant voltage (5 V). The temperature dependence of an electrical conductivity for In doped ZrS2 thin film shows Arrhenius behaviour consisting of high and low temperature regions with two distinct different conduction mechanisms shown in Fig. 6. Activation energy was calculated by taking slopes of linear plots in the low temperature. region and high temperature region. The activation energy for low temperature region is 0.033 eV and in high temperature region is 0.106 eV. The temperature dependence of the thermoelectric power of In doped ZrS2 thin film is shown in Fig. 7 which is negative and increases with increasing temperature. The negative sign indicates the material is n-type semiconductor. This is attributed to the fact that, intrinsically ZrS2 is n-type semiconductor. When trivalent impurity is added into ZrS2 lattice the zirconium ions are substituted by indium without distorting the structure, which is evident from XRD analysis. This eventually enhances the carrier concentra-
Fig. 6. Plot of ln vs. 1000/T for In:ZrS2 thin film.
A.M. Sargar et al. / Journal of Alloys and Compounds 474 (2009) 14–17
17
of bath concentration and other growth parameters. In doped ZrS2 thin films are polycrystalline with hexagonal crystal structure having direct band gap energy 1.78 eV. SEM micrograph shows densely packed spherical grains having average grain size of the material 310 nm. The EDS analysis indicates that the In is incorporated in ZrS2 thin film. Our results also show that the grown films are of a semiconducting nature with n-type conductivity. References
Fig. 7. Temperature dependence of the thermoelectric power of In:ZrS2 thin film.
tion which is evident from conductivity measurements. The doping concentration does not change the carrier type, provided that it enhances the carrier concentration. The retention of carrier type is supported by TEP measurement. 4. Conclusions The growth of polycrystalline In doped ZrS2 thin film is possible by a simple electrodeposition technique with the proper selection
[1] B. Pejova, I. Grozdanov, Thin Solid Films 408 (2002) 6. [2] J.P. Nair, N.B. Chaure, R. Jayakrishnan, R.R. Pandey, J. Mater. Sci. Mater. Electron. 12 (2001) 377. [3] S.K. Das, G.C. Morris, Sol. Energy Mater. Sol. Cells 28 (1993) 305. [4] R.B. Gore, S.K. Kulkarni, R.K. Pandey, J. Appl. Phys. 65 (1989) 2673. [5] R.K. Pandey, S.N. Sahu, S. Chandra, Handbook of Semiconductor Electrodeposition, Marcel Dekker, New York, USA, 1996. [6] M.E. Calixto, J.C. McClure, V.P. Singh, A. Bronson, P.J. Sebastain, X. Mathew, Sol. Energy Mater. Sol. Cells 63 (2003) 325. [7] P.C. Searson, T.P. Moffat, Crit. Rev. Surf. Chem. 3 (1994) 171. [8] W. Schwarzacher, D. Lasmore, IEEE Trans. Magn. 32 (1996) 3133. [9] T. Ikari, R. Provencher, S. Jandal, M. Aubin, Solid State Commun. 45 (1983) 113. [10] R. Provencher, R. Geagnon, S. Jandal, M. Aubin, J. Phys. C 21 (1988) 615. [11] C.D. Cavelle, G. Martinez, O. Gorochor, A. Zwick, J. Phys. C 15 (1982) 5371. [12] P.A. Lee, G. Said, R. Davis, Solid State Commun. 7 (1965) 1359. [13] W.R. McKinnon, J.R. Dahn, C. Levy-Clement, Solid State Commun. 50 (1984) 101. [14] B.G. Yacobi, F.W. Boswell, J.M. Corbett, Mater. Res. Bull. 14 (1979) 1033. [15] B. Subramanian, C. Snjeeviraja, M. Jayachandran, Mater. Chem. Phys. 71 (2001) 40. [16] N.S. Patil, A.M. Sargar, S.R. Mane, P.N. Bhosale, Appl. Surf. Sci. 254 (2008) 5261.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Optostructural and electrical studies on electrodeposited Indium doped ZrS2 thin films A.M. Sargar, N.S. Patil, S.R. Mane, S.N. Gawale, P.N. Bhosale ∗ Materials Research Laboratory, Department of Chemistry, Shivaji University, Kolhapur 416004, India
a r t i c l e
i n f o
Article history: Received 28 May 2008 Received in revised form 12 June 2008 Accepted 14 June 2008 Available online 8 August 2008 Keywords: Thin films Chemical synthesis Optical properties X-ray diffraction
a b s t r a c t Electrochemical deposition and characterization of indium doped zirconium disulphide (In:ZrS2 ) thin films deposited onto stainless steel and fluorine doped tin oxide (FTO) coated conducting glass plates from an aqueous bath containing ZrO(NO3 )2 , Na2 S2 O3 ·5H2 O and In2 (SO4 )3 is discussed in present manuscript. The prepared films were characterized by X-ray diffraction analysis (XRD), energy dispersive X-ray analysis (EDS), scanning electron microscopy (SEM) and optical absorption techniques. The structure was found to be hexagonal with preferential orientation along (1 0 2) plane. SEM study shows that the total substrate surface is well covered by densely packed spherical shaped grains. Optical absorption study shows the presence of direct transition having band gap energy 1.78 eV. In:ZrS2 is n-type semiconductor having activation energy, 0.033 eV in low temperature region and 0.106 eV in high temperature region. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Semiconducting thin film materials which is based on sulphide, selenides and tellurides, have attracted much attention for fabrication of solar cells and optoelectronic technology [1]. One of the main challenge in solar energy research is to find and fabricate the method that yield high quality thin films at low cost and easily scalable. The high quality thin films can be usually obtained by vaccum deposition, chemical bath deposition and electrodeposition [2–6]. Electrodeposition, also known as electrochemical deposition, or electrocrystallization, is one of the most useful technique for preparing thin films on the surface of conducting substrates [7,8]. An electrochemical technique has numerous advantages including low temperature processing, arbitrary substrate shapes, controllable film thickness, morphology and potential low capital cost. Thin films of ZrSe3 , [9] optical transmission in ZrS3−x Sex single crystals was reported by Provencher et al. [10]. Studies on thermorefelctance spectra of ZrS3−x Sex single crystal [11,12] lithium intercalation in LiX ZrS2 [13] and the fundamental absorption edge in NiX ZrS2 [14] is found in literature. To the best of our knowledge, no report is available for In doped ZrS2 thin film. In the present manuscript, we report, for the first time, the synthesis of Indium doped ZrS2 thin films by electrodeposition technique. Deposition was carried out by using zirconyl nitrate as
∗ Corresponding author. Tel.: +91 231 2609338; fax: +91 231 2691533, 2690333. E-mail address: p n [email protected] (P.N. Bhosale). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.06.077
source of zirconium ions, sodium thiosulphate as source of sulphur ions, and indium sulphate as indium ion source. The influence of growth conditions such as deposition potential, concentration of the constituents of the bath was studied in the initial stage. In order to characterize In doped ZrS2 thin films for their structural, compositional and optical properties; X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), and optical absorption techniques were employed.
2. Experimental In doped ZrS2 thin films were prepared by electrodeposition technique using aqueous solutions of 0.2 M ZrO(NO3 )2 , 0.1 M Na2 S2 O3 ·5H2 O and 0.1 M In2 (SO4 )3 . pH of the electrolytic bath was maintained at 1.9. Stainless steel and Fluorine doped tin oxide (SnO2 ) covered conducting glass plates of resistance 10 cm−1 were used as substrate support in this deposition. These conducting glasses of approximately 1 cm2 area were cleaned with detergent, dried and degreased with acetone and distilled water. The chemicals used in this deposition were of analytical grade. The electrochemical experiments were performed using Princeton PerkinElmer, Applied Research Verrsatat-II; Model 250/270 employing three electrode configurations, with stainless steel and tin oxide coated conducting glass substrate as cathode, graphite plate as anode and saturated calomel electrode (SCE) as reference electrode. Optical absorption was carried out in the range 350–850 nm with Hitachi-330 UV–vis-NIR spectrophotometer. Structure of the films was analyzed by X-ray diffractometer PW-1710 using Cu K␣ radiation ( = 1.5405 Å). Surface morphology and composition of the In doped ZrS2 thin film was studied by using scanning electron microscopy (JEOL JSM-6360) attached with an energy dispersive X-ray analyzer ((EDS). Electrical conductivity measurements in the range of 300–500 K as a function of temperature were performed on In doped ZrS2 thin films using two probe method. The measurement of thermoelectric power was done in the temperature range 300–500 K. For the electrical conductivity and TEP measurement silver contacts were made on the defined area of the film.
A.M. Sargar et al. / Journal of Alloys and Compounds 474 (2009) 14–17
15
Fig. 1. Cyclic voltammogram on stainless-steel substrate in the solution containing (a) 0.2 M ZrO(NO3 )2 ; (b) 0.1M Na2 S2 O3 ·5H2 O; (c) 0.1 M In2 (So4 )3 and (d) 0.2 M ZrO(NO3 )2 + 0.1 M Na2 S2 O3 ·5H2 O + 0.1 M In2 (So4 )3 .
3. Results and discussion 3.1. Cyclic voltammetry studies Preliminary investigations were carried out by cyclic voltammetric studies on deposition of In doped ZrS2 thin films. To optimise the conditions for deposition of Zr, In and S in an aqueous acidic medium, cyclic voltammogram of 0.2 M ZrO(NO3 )2 on stainless steel substrate is recorded and shown in Fig. 1a. It indicates, current start increasing and a cathodic peak is observed at about −0.960 V/SCE, this cathodic current flow is in association with zirconium(IV) reduction process. Fig. 1b shows cyclic voltammogram of 0.1 M Na2 S2 O3 ·5H2 O, reduction at about −0.63 V/SCE may be associated with reduction of thiosulphate ions. This reduction wave may be due to the S2 O3 2− ions released during the disproportionation of Na2 S2 O3 ·5H2 O [15]. Fig. 1c indicates a cyclic voltommogram of 0.1 M In2 (SO4 )3, reduction of elemental indium (In) occurs at a constant potential of −0.43 V/SCE. From the equilibrium electrode potentials of Zr, In and S, it can be seen that equilibrium electrode potential for the deposition of sulphur and indium is positive than that of zirconium deposition. Further, for simultaneous co-deposition of Zr, In and S, the respective electrolyte concentration should be adjusted high or low so as to bring the electrode potentials of all the deposits as closer as possible. Therefore, it is theoretically recommended to use a high concentration of Zr and low concentration for In and S, as deposition potential gets shifted to a negative value. Hence the deposition of In and S will become diffusition controlled due to the low concentration of indium sulphate and sodium thiosulphate. The cyclic voltammogram measured for the electrolytic bath of 0.2 M ZrO(NO3 )2 + 0.1 M Na2 S2 O3 ·5H2 O + 0.1 M In2 (SO4 )3 is shown in Fig. 1d, the reduction potential of −0.850 V/SCE was found to be optimum for the uniform and well adherent In:ZrS2 thin films.
where Eg is the band gap, ˛ the absorption coefficient, the frequency, A is the constant and n can take values 1/2, 3/2, 2 and 3 depending on the mode of transition. Here n = 1/2 offers the best fit for the optical absorption data of In:ZrS2 thin films. The plot of (˛h)2 versus h shown in Fig. 2 is almost linear at higher wavelength and the optical absorption coefficient is of the order of 105 cm−1 supporting the allowed direct band transition of the material. The band gap is determined near the absorption edge by extrapolating the straight portion of the plot to the energy axis and direct band gap energy value was found to be 1.78 eV. 3.3. X-ray diffraction studies Fig. 3 shows XRD pattern of the electrodeposited In:ZrS2 thin film prepared at −0.85 V for the deposition time of 30 min. There are no standard JCPDS data available for Indium doped zirconium disulphide. Hence the plane indices are obtained from comparison between observed ‘d’ values and standard ‘d’ values for ZrS2 and In2 S3 which are given by JCPDS file nos. 11-0679 and 33-0623. It is observed that, the XRD pattern consists of peaks corresponding hexagonal crystallographic planes. From the XRD analysis it is observed that, no separate phase formation of In2 S3 was observed in In:ZrS2 thin films. Table 1 lists the comparison between observed ‘d’ and standard ‘d’ values for In doped ZrS2 thin films. The crystallite size (grain diameter) ‘D’ of the deposits was calculated from the
3.2. Optical absorption studies The room temperature optical absorption was measured for the as-grown In:ZrS2 thin films in the wavelength region of 350–850 nm. The optical absorption coefficient (˛) of In:ZrS2 thin film was calculated using the absorbance value measured for a particular wavelength () and film thickness (t) using the equation: ˛h = A(h − Eg )
n
Fig. 2. Plot of (˛h)2 vs. h for In:ZrS2 thin film deposited at room temperature.
16
A.M. Sargar et al. / Journal of Alloys and Compounds 474 (2009) 14–17
Fig. 3. XRD pattern of as deposited In:ZrS2 thin film at room temperature. Table 1 Comparison of observed ‘d’ values with standard ‘d’ values for In doped ZrS2 thin films Serial number
Observed ‘d’ value (Å)
Standard ‘d’ value (Å)
(h k l) planes
1 2 3 4 5
2.126 1.826 1.452 1.311 1.167
2.14 1.828 1.456 1.332 1.165
102 110 004 113 005
full-width at half-maximum (FWHM) for more intense peak (1 0 2) is 24 nm using the Scherrer formula [16]. 3.4. SEM/EDS studies Fig. 4 shows the scanning electron micrograph of the In:ZrS2 thin film. Densely packed spherical grains are mixed with clusters, which mean that some of the grains are not well developed. The micrograph also reveals that, the material shows compact, large number of spherical grains distributed over the entire surface of the substrate. To analyse atomic percentage of In:ZrS2 thin film EDS technique was used and Fig. 5 shows the EDS pattern of In doped ZrS2 thin
Fig. 4. SEM image of as deposited In:ZrS2 thin film at room temperature.
Fig. 5. EDS analysis of as deposited In:ZrS2 thin film on stainless-steel substrate.
film. The EDS spectrum shows the presence of Zr, In, and S in the film. The atomic percentage for Zr, S and In obtained from the EDS analysis is 36.10, 62.08 and 01.82 respectively. 3.5. Electrical/TEP studies Electrical behaviour was studied by using two-point probe technique, varying the temperature range 300–500 K, under constant voltage (5 V). The temperature dependence of an electrical conductivity for In doped ZrS2 thin film shows Arrhenius behaviour consisting of high and low temperature regions with two distinct different conduction mechanisms shown in Fig. 6. Activation energy was calculated by taking slopes of linear plots in the low temperature. region and high temperature region. The activation energy for low temperature region is 0.033 eV and in high temperature region is 0.106 eV. The temperature dependence of the thermoelectric power of In doped ZrS2 thin film is shown in Fig. 7 which is negative and increases with increasing temperature. The negative sign indicates the material is n-type semiconductor. This is attributed to the fact that, intrinsically ZrS2 is n-type semiconductor. When trivalent impurity is added into ZrS2 lattice the zirconium ions are substituted by indium without distorting the structure, which is evident from XRD analysis. This eventually enhances the carrier concentra-
Fig. 6. Plot of ln vs. 1000/T for In:ZrS2 thin film.
A.M. Sargar et al. / Journal of Alloys and Compounds 474 (2009) 14–17
17
of bath concentration and other growth parameters. In doped ZrS2 thin films are polycrystalline with hexagonal crystal structure having direct band gap energy 1.78 eV. SEM micrograph shows densely packed spherical grains having average grain size of the material 310 nm. The EDS analysis indicates that the In is incorporated in ZrS2 thin film. Our results also show that the grown films are of a semiconducting nature with n-type conductivity. References
Fig. 7. Temperature dependence of the thermoelectric power of In:ZrS2 thin film.
tion which is evident from conductivity measurements. The doping concentration does not change the carrier type, provided that it enhances the carrier concentration. The retention of carrier type is supported by TEP measurement. 4. Conclusions The growth of polycrystalline In doped ZrS2 thin film is possible by a simple electrodeposition technique with the proper selection
[1] B. Pejova, I. Grozdanov, Thin Solid Films 408 (2002) 6. [2] J.P. Nair, N.B. Chaure, R. Jayakrishnan, R.R. Pandey, J. Mater. Sci. Mater. Electron. 12 (2001) 377. [3] S.K. Das, G.C. Morris, Sol. Energy Mater. Sol. Cells 28 (1993) 305. [4] R.B. Gore, S.K. Kulkarni, R.K. Pandey, J. Appl. Phys. 65 (1989) 2673. [5] R.K. Pandey, S.N. Sahu, S. Chandra, Handbook of Semiconductor Electrodeposition, Marcel Dekker, New York, USA, 1996. [6] M.E. Calixto, J.C. McClure, V.P. Singh, A. Bronson, P.J. Sebastain, X. Mathew, Sol. Energy Mater. Sol. Cells 63 (2003) 325. [7] P.C. Searson, T.P. Moffat, Crit. Rev. Surf. Chem. 3 (1994) 171. [8] W. Schwarzacher, D. Lasmore, IEEE Trans. Magn. 32 (1996) 3133. [9] T. Ikari, R. Provencher, S. Jandal, M. Aubin, Solid State Commun. 45 (1983) 113. [10] R. Provencher, R. Geagnon, S. Jandal, M. Aubin, J. Phys. C 21 (1988) 615. [11] C.D. Cavelle, G. Martinez, O. Gorochor, A. Zwick, J. Phys. C 15 (1982) 5371. [12] P.A. Lee, G. Said, R. Davis, Solid State Commun. 7 (1965) 1359. [13] W.R. McKinnon, J.R. Dahn, C. Levy-Clement, Solid State Commun. 50 (1984) 101. [14] B.G. Yacobi, F.W. Boswell, J.M. Corbett, Mater. Res. Bull. 14 (1979) 1033. [15] B. Subramanian, C. Snjeeviraja, M. Jayachandran, Mater. Chem. Phys. 71 (2001) 40. [16] N.S. Patil, A.M. Sargar, S.R. Mane, P.N. Bhosale, Appl. Surf. Sci. 254 (2008) 5261.