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Structural and optical characterization of Sb-doped CuInS2 thin films grown by vacuum evaporation method
Journal of Physics and Chemistry of Solids 64 (2003) 1863–1867 www.elsevier.com/locate/jpcs
Structural and optical characterization of Sb-doped CuInS2 thin films grown by vacuum evaporation method Y. Akakia,b,*, H. Komakib, H. Yokoyamab, K. Yoshinob, K. Maedab, T. Ikarib b
a Miyakonojo National College of Technology, 473-1 Yoshio, Miyakonojo, Miyazaki 885-8567, Japan Department of Electrical and Electronic Engineering, Miyazaki University, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan
Abstract Structural, electrical and optical properties of Sb-doped CuInS2 thin films grown by single source thermal evaporation method were studied. The films were annealed from 100 to 500 8C in air after the evaporation. The X-ray diffraction spectra indicated that polycrystalline CuInS2 films were successfully obtained by annealing above 200 8C. This temperature was lower than that of non-doped CuInS2 films. Furthermore, We found that the Sb-doped CuInS2 thin films became close to stoichiometry in comparison with non-doped CuInS2 thin films. The Sb-doped samples annealed above 200 8C has bandgap energy of 1.43– 1.50 eV. q 2003 Elsevier Ltd. All rights reserved. Keywords: C. X-ray diffraction
1. Introduction Solar cell technologies using I-III-VI2 chalcopyrite semiconductor have made rapid progress in recent years. In particular, CuInGaSe2 (CIGS) based solar cells have been extensively reported in comparison with other chalcopyrite semiconductor based solar cells. Conversion efficiencies for polycrystalline CIGS based solar cells have been significantly improved over recent years and the best cell is now reported at 18.8% [1]. However, among ternary chalcopyrite semiconductors, CuInS2 may be the most promising material for photovoltaic applications due to the bandgap energy of 1.53 eV [2] which perfectly matches the solar spectrum for energy conversion and to its large absorption coefficient above the bandgap energy. Furthermore, since the material does not contain toxic Ga or Se atoms, this may have an advantage in comparison with the frequently studied CuInSe2 and CuInGaSe2. The non-doped CuInS2 crystals prepared by many methods have been investigated. For controlling a conduction type and obtaining a low resistivity, several impurities * Corresponding author. Miyakonojo National College of Technology, 473-1 Yoshio, Miyakonojo, Miyazaki 885-8567, Japan. E-mail address: [email protected] (Y. Akaki).
doped CuInS2 bulks have also been studied [3 – 5]. Several methods of depositing CuInS2 polycrystalline thin films, evaporation [6], chemical vapor deposition (CVD) [7], sputtering, [8] spray pyrolysis [9], have been investigated. The films grown by these methods have been studied on structural, electrical and optical properties. However, there were a few reports on doped CuInS2 thin films. In our previous paper [10], single source thermal evaporation technique was carried out for CuInS2 films on the glass substrate, and the films were subsequently annealed from 100 to 500 8C in air. From X-ray diffraction (XRD) spectra, the polycrystalline CuInS2 thin films begin to grow by annealing at 300 8C. In this paper, we report on structural, electrical and optical properties of the Sb-doped CuInS2 thin films grown by the single source thermal evaporation method. Furthermore, we also compare Sbdoped thin films with the non-doped ones.
2. Experimental procedure Evaporated thin films were deposited on glass substrates from non-doped and Sb (1.2, 3.5 and 5.7 mol %)-doped CuInS2 powder by single source vacuum evaporation using the resistivity heated alumina crucible boats. The bulk nondoped and Sb-doped bulk CuInS2 ingots were grown by
0022-3697/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0022-3697(03)00249-X
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Y. Akaki et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1863–1867
Hot-Press (HP) method at 700 8C for 1 h under high pressure at 22.5 MPa from stoichiometric Cu2S and In2S3 powders [11,12]. A pressure during the evaporation was maintained at 1 £ 1025 Torr. After the evaporation, the films were annealed at the temperature from 100 to 500 8C for 30 min. The thickness of the films was 0.78– 1.05 mm. The samples were examined by XRD, electron probe microanalysis (EPMA), thermo probe analysis, optical transmission measurements and sheet rsistivity measurement by fourpoint probe method.
3. Results and discussion Fig. 1 shows the XRD patterns for the Sb-doped (1.2 mol %) samples annealed at several temperatures for 30 min. in air. By annealing at 200 8C for 30 min, three peaks are strongly observed at 27.9, 46.6, and 55.1 8. They are well identified with (112), (204)/(220), and (116)/(312) diffraction lines, respectively, for CuInS2 in comparison with the Joint Committee of Powder Diffraction Standard (JCPDS) card [13]. Since the films annealed below 300 8C also show additional diffraction peaks at 26.4 and 29.9 8 and 43.3, 50.4 and 74.1 8, that can be associated to binary compounds In6S7 and Cu crystal, respectively. It is considered that the solidstate reaction that leads to the formation of CuInS2 films is incomplete. However, when the samples were annealed above 400 8C in air, the mixed phase of CuInS2 crystal and In2O3 crystal appeared. I think that the single phase of CuInS2 thin film can be prepared. Because the unnecessary In2O3 phase may be disappeared in samples that is annealed in Ar or N2. The parameters of a-axis of the samples
˚ ) annealed above 200 8C are larger than that (5.524– 5.546 A ˚ ) [13]. The parameters of a-axis of of JCPDS card (5.523 A JCPDS card is closed with increase the annealing temperature of the sample; that of the samples annealed at 500 8C ˚ . On the other hand, the parameters of c are 5.524– 5.532 A ˚ ) are smaller than axis of these samples (11.000 – 11.091 A ˚ ) [13]. The more increasing that of JCPDS card (11.141 A the annealing temperature of the sample is, the closer the parameters of c-axis of JCPDS card is; that of the samples ˚ . Fig. 2 shows the annealed at 500 8C are 11.058 –11.091 A XRD patterns of Sb-doped and non-doped CuInS2 thin films after annealing at 500 8C for 30 min. in air. We have already reported that unexpected CuIn11S17 phase still remained for the non-doped sample annealed at 500 8C [10]. However, the samples doped with Sb atom above 3.5 mol % by annealing above 400 8C were excepted the unexpected phase. Fig. 3 shows the EPMA results of average of five measuring points on surface of non-doped and Sb-doped (5.7 mol %) CuInS2 thin films. The circles, triangles, squares and rhombuses in the figure indicate Cu, In, S and Sb atm % in the films, respectively. The open and closed symbols are the each atomic concentration of the non-doped and Sb-doped samples, respectively. The dot lines indicate stoichiometric values of CuInS2. The presence of Sb atom is shown in all polycrystalline CuInS2 thin films. Cu and In compositions in the Sb-doped CuInS2 thin films became closer to stoichiometry than that for the non-doped ones. However, S composition in the Sb-doped CuInS2 thin films decrease more than that of non-doped sample. One notes here that Sb-doped CuInS2 thin films become Cu-rich below 200 8C and In-rich above 300 8C. When it is generally evaporated to compound materials, these are resolved. In
Fig. 1. X-ray diffraction patterns of evaporated Sb-doped (1.2 mol %) CuInS2 thin films after annealing in air; Cu crystals (circles), In6S7 crystals (triangles), In2O3 crystals (squares), CuIn11S17 crystals (rhombuses).
Y. Akaki et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1863–1867
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Fig. 2. X-ray diffraction patterns of Sb-doped and non-doped CuInS2 thin films after annealing at 500 8C in air; In2O3 crystals (squares), CuIn11S17 crystals (rhombuses).
this case, In– S based materials are first evaporated from the single source on the glass substrate, and Cu– S based materials are immediately deposited on the In– S based materials. Therefore CuInS2 thin films by annealing below 100 8C were Cu-rich. On the other hand, the EPMA results indicate In-rich for the CuInS2 thin films by annealing above 200 8C. It is considered that a solid-state reaction might be led that the CuInS2 thin films are annealed above 200 8C. Thermo probe analysis is also carried out for the non-doped and Sb-doped CuInS2 thin film samples. Both non-doped
and Sb-doped samples annealed above 300 8C show n-type conductivity. Since there are so many intrinsic donors such as In interstitial (Ini) and/or S vacancy defect, we consider that the introduced Sb acceptor cannot compensate the donors. The absorption coefficient a were calculated from transmission spectra in the wavelength range of 400– 1200 nm and reflection coefficient calculated from refractive index of n ¼ 2:8 [14,15]. The bandgap energy ðEgÞ of the samples are estimated from a plotting of ðahnÞ2 versus
Fig. 3. Electron probe microanalysis of Sb-doped (5.7 mol.%) and non-doped CuInS2 thin films after annealing for 30 min. in air.
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Fig. 4. Relationship between ðahnÞ2 and photon energy for non-doped and Sb-doped CuInS2 thin films by annealing at 300 8C in air.
photon energy (Fig. 4). Fig. 5 shows the relationship between Eg and annealing temperatures of all samples annealed at over 200 8C. The Eg for the polycrystalline Sbdoped CuInS2 thin films obtained by annealing above 200 8C can be estimated to be about 1.43 – 1.50 eV. The values are almost the same as the obtained value from the films prepared by the other methods [15– 17]. Fig. 6 shows the relationship between resistivities and annealed temperatures of non-doped and Sb-doped CuInS2 thin films after annealing for 30 min. in air. All samples indicate low resistivites, and the characteristics between Sb-doped and non-doped samples were similar. One of the reasons is that the concentration of donor and/or acceptor
impurities in all CuInS2 samples may not change by Sbdoping. As-deposited films and the films obtained by annealing at 100 8C indicate low resistivities. It is deduced that the low resistivities of the films are due to Cu metals in the samples shown Fig. 1. The samples annealed at 300 8C show the maximum of resistivity. Because the samples annealed below 200 8C that indicated p-type conduction changed n-type conduction by annealing above 300 8C; the net carrier concentration in the films decreased. The higher the annealing temperature of samples above 300 8C is, the lower the resistivity of samples is. We deduced that the grain size of polycrystalline CuInS2 became big with increasing the annealing
Fig. 5. Relationship between bandgap energies and annealing temperatures of non-doped and Sb-doped CuInS2 thin films after annealing in air.
Y. Akaki et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1863–1867
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Fig. 6. Relationship between sheet resistivities and annealing temperatures of non-doped and Sb-doped CuInS2 thin films after annealing in air.
temperatures above 300 8C and/or the net carrier concentration in the films increased.
4. Conclusion Structural, electrical and optical properties of non-doped and Sb-doped CuInS2 thin films grown by single source thermal evaporation method were studied. By Sb-doping, the polycrystalline CuInS2 thin films were grown by annealing above 200 8C. The Sb-doped sample might become a single phase of CuInS2 by annealing above 400 8C in Ar or N2. Furthermore, the Sb-doped films became close to stoichiometry in comparison with non-doped CuInS2 thin films. The Sb-doped samples annealed above 200 8C has bandgap energy of 1.43 – 1.50 eV.
References [1] A. Contreras, B. Egaas, K. Pamanathan, J. Hiltner, A. Swartzlander, F. Hasoon, R. Noufi, Prog. Photovol. Res. Appl. 7 (1999) 311. [2] J.L. Shay, B. Tell, H.M. Kasper, L.M. Schiavone, Phys. Rev. B. 5 (1972) 5003. [3] G. Brandt, A. Ranber, J. Schneider, Solid State Commun. 12 (1973) 481.
[4] J.J.M. Binsma, L.J. Giling, J. Bloem, J. Luminescence 27 (1982) 35. [5] S.D. Mittleman, R. Singh, Solid State Commun. 22 (1977) 659. [6] L.L. Kazmerski, M.S. Ayyagari, G.A. Sanborn, J. Appl. Phys. 46 (1975) 4865. [7] H.L. Hwang, C.Y. Sun, C.S. Fang, S.D. Chang, C.H. Cheng, M.H. Yang, H.H. Lin, T. Tuwan-mu, J. Crystal Growth 55 (1981) 116. [8] H.L. Hwang, C.L. Cheng, L.M. Liu, Y.C. Liu, C.Y. Sun, Thin Solid Films 67 (1980) 83. [9] B. Pamplin, R.S. Feigelson, Thin Solid Films 60 (1979) 141. [10] Y. Akaki, H. Komaki, K. Yoshino, T. Ikari, J. Vac. Sci. Tech. A 20 (2002) 1486. [11] H. Komaki, K. Yoshino, S. Seto, M. Yoneta, Y. Akaki, T. Ikari, J. Crystal Growth 236 (2002) 256. [12] H. Komaki, Y. Akaki, K. Yoshino, S. Seto, M. Yoneta, T. Ikari, Proc. ICTMC-13, Paris, 2002. [13] JCPDS file No. 27-0159. [14] J.L. Shay, J.H. Wernick, Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties and Applications, Pergamon Press, New York, 1975. [15] J. Gonzalez-Hernandez, P.M. Gorley, P.P. Horley, O.M. Vartsabyuk, Yu.V. Vorobiev, Thin Solid Films 403 (2002) 471. [16] Y.B. He, A. Polity, H.R. Alves, I. Osterreicher, W. Kriegseis, D. Pfisterer, B.K. Meyer, Thin Solid Films. 403 (2002) 62. [17] T. Wada, T. Negami, M. Nishitani, Appl. Phys. Lett. 62 (1983) 1943.
Structural and optical characterization of Sb-doped CuInS2 thin films grown by vacuum evaporation method Y. Akakia,b,*, H. Komakib, H. Yokoyamab, K. Yoshinob, K. Maedab, T. Ikarib b
a Miyakonojo National College of Technology, 473-1 Yoshio, Miyakonojo, Miyazaki 885-8567, Japan Department of Electrical and Electronic Engineering, Miyazaki University, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan
Abstract Structural, electrical and optical properties of Sb-doped CuInS2 thin films grown by single source thermal evaporation method were studied. The films were annealed from 100 to 500 8C in air after the evaporation. The X-ray diffraction spectra indicated that polycrystalline CuInS2 films were successfully obtained by annealing above 200 8C. This temperature was lower than that of non-doped CuInS2 films. Furthermore, We found that the Sb-doped CuInS2 thin films became close to stoichiometry in comparison with non-doped CuInS2 thin films. The Sb-doped samples annealed above 200 8C has bandgap energy of 1.43– 1.50 eV. q 2003 Elsevier Ltd. All rights reserved. Keywords: C. X-ray diffraction
1. Introduction Solar cell technologies using I-III-VI2 chalcopyrite semiconductor have made rapid progress in recent years. In particular, CuInGaSe2 (CIGS) based solar cells have been extensively reported in comparison with other chalcopyrite semiconductor based solar cells. Conversion efficiencies for polycrystalline CIGS based solar cells have been significantly improved over recent years and the best cell is now reported at 18.8% [1]. However, among ternary chalcopyrite semiconductors, CuInS2 may be the most promising material for photovoltaic applications due to the bandgap energy of 1.53 eV [2] which perfectly matches the solar spectrum for energy conversion and to its large absorption coefficient above the bandgap energy. Furthermore, since the material does not contain toxic Ga or Se atoms, this may have an advantage in comparison with the frequently studied CuInSe2 and CuInGaSe2. The non-doped CuInS2 crystals prepared by many methods have been investigated. For controlling a conduction type and obtaining a low resistivity, several impurities * Corresponding author. Miyakonojo National College of Technology, 473-1 Yoshio, Miyakonojo, Miyazaki 885-8567, Japan. E-mail address: [email protected] (Y. Akaki).
doped CuInS2 bulks have also been studied [3 – 5]. Several methods of depositing CuInS2 polycrystalline thin films, evaporation [6], chemical vapor deposition (CVD) [7], sputtering, [8] spray pyrolysis [9], have been investigated. The films grown by these methods have been studied on structural, electrical and optical properties. However, there were a few reports on doped CuInS2 thin films. In our previous paper [10], single source thermal evaporation technique was carried out for CuInS2 films on the glass substrate, and the films were subsequently annealed from 100 to 500 8C in air. From X-ray diffraction (XRD) spectra, the polycrystalline CuInS2 thin films begin to grow by annealing at 300 8C. In this paper, we report on structural, electrical and optical properties of the Sb-doped CuInS2 thin films grown by the single source thermal evaporation method. Furthermore, we also compare Sbdoped thin films with the non-doped ones.
2. Experimental procedure Evaporated thin films were deposited on glass substrates from non-doped and Sb (1.2, 3.5 and 5.7 mol %)-doped CuInS2 powder by single source vacuum evaporation using the resistivity heated alumina crucible boats. The bulk nondoped and Sb-doped bulk CuInS2 ingots were grown by
0022-3697/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0022-3697(03)00249-X
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Y. Akaki et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1863–1867
Hot-Press (HP) method at 700 8C for 1 h under high pressure at 22.5 MPa from stoichiometric Cu2S and In2S3 powders [11,12]. A pressure during the evaporation was maintained at 1 £ 1025 Torr. After the evaporation, the films were annealed at the temperature from 100 to 500 8C for 30 min. The thickness of the films was 0.78– 1.05 mm. The samples were examined by XRD, electron probe microanalysis (EPMA), thermo probe analysis, optical transmission measurements and sheet rsistivity measurement by fourpoint probe method.
3. Results and discussion Fig. 1 shows the XRD patterns for the Sb-doped (1.2 mol %) samples annealed at several temperatures for 30 min. in air. By annealing at 200 8C for 30 min, three peaks are strongly observed at 27.9, 46.6, and 55.1 8. They are well identified with (112), (204)/(220), and (116)/(312) diffraction lines, respectively, for CuInS2 in comparison with the Joint Committee of Powder Diffraction Standard (JCPDS) card [13]. Since the films annealed below 300 8C also show additional diffraction peaks at 26.4 and 29.9 8 and 43.3, 50.4 and 74.1 8, that can be associated to binary compounds In6S7 and Cu crystal, respectively. It is considered that the solidstate reaction that leads to the formation of CuInS2 films is incomplete. However, when the samples were annealed above 400 8C in air, the mixed phase of CuInS2 crystal and In2O3 crystal appeared. I think that the single phase of CuInS2 thin film can be prepared. Because the unnecessary In2O3 phase may be disappeared in samples that is annealed in Ar or N2. The parameters of a-axis of the samples
˚ ) annealed above 200 8C are larger than that (5.524– 5.546 A ˚ ) [13]. The parameters of a-axis of of JCPDS card (5.523 A JCPDS card is closed with increase the annealing temperature of the sample; that of the samples annealed at 500 8C ˚ . On the other hand, the parameters of c are 5.524– 5.532 A ˚ ) are smaller than axis of these samples (11.000 – 11.091 A ˚ ) [13]. The more increasing that of JCPDS card (11.141 A the annealing temperature of the sample is, the closer the parameters of c-axis of JCPDS card is; that of the samples ˚ . Fig. 2 shows the annealed at 500 8C are 11.058 –11.091 A XRD patterns of Sb-doped and non-doped CuInS2 thin films after annealing at 500 8C for 30 min. in air. We have already reported that unexpected CuIn11S17 phase still remained for the non-doped sample annealed at 500 8C [10]. However, the samples doped with Sb atom above 3.5 mol % by annealing above 400 8C were excepted the unexpected phase. Fig. 3 shows the EPMA results of average of five measuring points on surface of non-doped and Sb-doped (5.7 mol %) CuInS2 thin films. The circles, triangles, squares and rhombuses in the figure indicate Cu, In, S and Sb atm % in the films, respectively. The open and closed symbols are the each atomic concentration of the non-doped and Sb-doped samples, respectively. The dot lines indicate stoichiometric values of CuInS2. The presence of Sb atom is shown in all polycrystalline CuInS2 thin films. Cu and In compositions in the Sb-doped CuInS2 thin films became closer to stoichiometry than that for the non-doped ones. However, S composition in the Sb-doped CuInS2 thin films decrease more than that of non-doped sample. One notes here that Sb-doped CuInS2 thin films become Cu-rich below 200 8C and In-rich above 300 8C. When it is generally evaporated to compound materials, these are resolved. In
Fig. 1. X-ray diffraction patterns of evaporated Sb-doped (1.2 mol %) CuInS2 thin films after annealing in air; Cu crystals (circles), In6S7 crystals (triangles), In2O3 crystals (squares), CuIn11S17 crystals (rhombuses).
Y. Akaki et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1863–1867
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Fig. 2. X-ray diffraction patterns of Sb-doped and non-doped CuInS2 thin films after annealing at 500 8C in air; In2O3 crystals (squares), CuIn11S17 crystals (rhombuses).
this case, In– S based materials are first evaporated from the single source on the glass substrate, and Cu– S based materials are immediately deposited on the In– S based materials. Therefore CuInS2 thin films by annealing below 100 8C were Cu-rich. On the other hand, the EPMA results indicate In-rich for the CuInS2 thin films by annealing above 200 8C. It is considered that a solid-state reaction might be led that the CuInS2 thin films are annealed above 200 8C. Thermo probe analysis is also carried out for the non-doped and Sb-doped CuInS2 thin film samples. Both non-doped
and Sb-doped samples annealed above 300 8C show n-type conductivity. Since there are so many intrinsic donors such as In interstitial (Ini) and/or S vacancy defect, we consider that the introduced Sb acceptor cannot compensate the donors. The absorption coefficient a were calculated from transmission spectra in the wavelength range of 400– 1200 nm and reflection coefficient calculated from refractive index of n ¼ 2:8 [14,15]. The bandgap energy ðEgÞ of the samples are estimated from a plotting of ðahnÞ2 versus
Fig. 3. Electron probe microanalysis of Sb-doped (5.7 mol.%) and non-doped CuInS2 thin films after annealing for 30 min. in air.
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Fig. 4. Relationship between ðahnÞ2 and photon energy for non-doped and Sb-doped CuInS2 thin films by annealing at 300 8C in air.
photon energy (Fig. 4). Fig. 5 shows the relationship between Eg and annealing temperatures of all samples annealed at over 200 8C. The Eg for the polycrystalline Sbdoped CuInS2 thin films obtained by annealing above 200 8C can be estimated to be about 1.43 – 1.50 eV. The values are almost the same as the obtained value from the films prepared by the other methods [15– 17]. Fig. 6 shows the relationship between resistivities and annealed temperatures of non-doped and Sb-doped CuInS2 thin films after annealing for 30 min. in air. All samples indicate low resistivites, and the characteristics between Sb-doped and non-doped samples were similar. One of the reasons is that the concentration of donor and/or acceptor
impurities in all CuInS2 samples may not change by Sbdoping. As-deposited films and the films obtained by annealing at 100 8C indicate low resistivities. It is deduced that the low resistivities of the films are due to Cu metals in the samples shown Fig. 1. The samples annealed at 300 8C show the maximum of resistivity. Because the samples annealed below 200 8C that indicated p-type conduction changed n-type conduction by annealing above 300 8C; the net carrier concentration in the films decreased. The higher the annealing temperature of samples above 300 8C is, the lower the resistivity of samples is. We deduced that the grain size of polycrystalline CuInS2 became big with increasing the annealing
Fig. 5. Relationship between bandgap energies and annealing temperatures of non-doped and Sb-doped CuInS2 thin films after annealing in air.
Y. Akaki et al. / Journal of Physics and Chemistry of Solids 64 (2003) 1863–1867
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Fig. 6. Relationship between sheet resistivities and annealing temperatures of non-doped and Sb-doped CuInS2 thin films after annealing in air.
temperatures above 300 8C and/or the net carrier concentration in the films increased.
4. Conclusion Structural, electrical and optical properties of non-doped and Sb-doped CuInS2 thin films grown by single source thermal evaporation method were studied. By Sb-doping, the polycrystalline CuInS2 thin films were grown by annealing above 200 8C. The Sb-doped sample might become a single phase of CuInS2 by annealing above 400 8C in Ar or N2. Furthermore, the Sb-doped films became close to stoichiometry in comparison with non-doped CuInS2 thin films. The Sb-doped samples annealed above 200 8C has bandgap energy of 1.43 – 1.50 eV.
References [1] A. Contreras, B. Egaas, K. Pamanathan, J. Hiltner, A. Swartzlander, F. Hasoon, R. Noufi, Prog. Photovol. Res. Appl. 7 (1999) 311. [2] J.L. Shay, B. Tell, H.M. Kasper, L.M. Schiavone, Phys. Rev. B. 5 (1972) 5003. [3] G. Brandt, A. Ranber, J. Schneider, Solid State Commun. 12 (1973) 481.
[4] J.J.M. Binsma, L.J. Giling, J. Bloem, J. Luminescence 27 (1982) 35. [5] S.D. Mittleman, R. Singh, Solid State Commun. 22 (1977) 659. [6] L.L. Kazmerski, M.S. Ayyagari, G.A. Sanborn, J. Appl. Phys. 46 (1975) 4865. [7] H.L. Hwang, C.Y. Sun, C.S. Fang, S.D. Chang, C.H. Cheng, M.H. Yang, H.H. Lin, T. Tuwan-mu, J. Crystal Growth 55 (1981) 116. [8] H.L. Hwang, C.L. Cheng, L.M. Liu, Y.C. Liu, C.Y. Sun, Thin Solid Films 67 (1980) 83. [9] B. Pamplin, R.S. Feigelson, Thin Solid Films 60 (1979) 141. [10] Y. Akaki, H. Komaki, K. Yoshino, T. Ikari, J. Vac. Sci. Tech. A 20 (2002) 1486. [11] H. Komaki, K. Yoshino, S. Seto, M. Yoneta, Y. Akaki, T. Ikari, J. Crystal Growth 236 (2002) 256. [12] H. Komaki, Y. Akaki, K. Yoshino, S. Seto, M. Yoneta, T. Ikari, Proc. ICTMC-13, Paris, 2002. [13] JCPDS file No. 27-0159. [14] J.L. Shay, J.H. Wernick, Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties and Applications, Pergamon Press, New York, 1975. [15] J. Gonzalez-Hernandez, P.M. Gorley, P.P. Horley, O.M. Vartsabyuk, Yu.V. Vorobiev, Thin Solid Films 403 (2002) 471. [16] Y.B. He, A. Polity, H.R. Alves, I. Osterreicher, W. Kriegseis, D. Pfisterer, B.K. Meyer, Thin Solid Films. 403 (2002) 62. [17] T. Wada, T. Negami, M. Nishitani, Appl. Phys. Lett. 62 (1983) 1943.