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Structural and optical properties of sprayed CuInS2 thin films
24
Materials Chemistry and Physics, 34 (1993) 24-27
Structural H. Bihri,
and optical properties
C. Messaoudi,
D. Sayah,
of sprayed CuInS, thin films
M. Abd-Lefdil
Physics Department, Faculty of Sciences, Universite’ Mohamme4
Rabat (Morocco)
and M. Cad&e Laboratoire d’lnfrarouge, Universitk des Sciences et Techniques du Languedoc, Place Eugkne Bataillon, 34095 Montpellier (France) Presented at the 3rd Meeting on the Science of Materials, 27th-29th October 1991, Oran (Algeria) (Received
February
26, 1992; accepted
July 29, 1992)
Abstract p-type CuInSz thin films of about 1 pm were prepared by the spray pyrolysis method. The Cu:In ratios in the spray solution was varied in order to produce good quality single phase CuInSr films. X-ray analysis showed that the film sprayed with a Cu:In ratio equal to 1 in the spraying mixture presented a single phase CuInS, with a chalcopyrite structure, and oriented preferentially with (112) planes parallel to the substrate. The surface morphology of the deposited films changed with the copper content. The optical band gap at room temperature was around 1.45 eV. The Hall effect measurements were studied.
Introduction
Experimental
CuInS, ternary semiconductors have been extensively studied in recent years because of their promising applications especially for the photovoltaic conversion. The direct band gap of about 1.5 eV [l] is close to the optimum value for solar energy conversion. CuInS, can be synthesised in both n- and p-type semiconductors. Its homojunction has been predicted to yield a theoretical efficiency of 27-32% [2]. Several techniques have been reported for the preparation of thin CuInS, films, namely single and doublesource evaporation [3], r.f. sputtering [4], flash evaporation [5, 61, chemical vapour deposition [7, 81 and spray pyrolysis [9, lo]. A thin film solar cell totally sprayed with CuInS,/Cd(Zn)S with an efficiency of 2.6% has been described by Rajaram et al. [ll]. Kazmerski et al. [12] have reported an efficiency of 3.6% for CuInSJCdS using CuInS, prepared by means of double-source evaporation. It has also been reported that single-source evaporation does not produce good quality single phase CuInS, films [13]. For large scale production only spray pyrolysis and sulphurization of CuIn layers seem to be useful. The purpose of this work is to report the physical characteristics of sprayed CuInS, thin films, prepared by varying the copper to indium ratio in the starting spray solution.
A starting solution containing the desired cations with sulphur, indium and copper respectively in the form of thiourea, indium trichloride and cuprous chloride at a concentration of 0.005 M was used. This starting solution was sprayed in a fine mist on to clean glass substrates heated to 570-670 K. A schematic diagram of our set-up is shown in Fig. 1.
0254-0584/93/$6.00
2
8T 1
+I
+3-
d
5
6
7
: Fig. 1. A schematic of the chemical spraying set-up. 1, Spraying solution; 2, pump flowmeter; 3, nozzle waggon; 4, air pump; 5, nozzle; 6, aspiration chamber; 7, glass substrates; 8, hot plate; 9, temperature controller.
0 1993 - Elsevier Sequoia. All rights reserved
A preliminary investigation showed that good and reproducible films could be obtained using a spray-rate of 5 cc min-l and a substrate temperature of around 620 K. This would yield a deposition rate about 50 nm min-I. For the purpose of studying the effect of the copper to indium ratio, the films had been deposited with Cu:In ratio in the 0.8-1.3 range. The structure of the thin films of CuInS, was determined from X-ray diffraction; their composition by the electron probe micro-analysis (EPMA), and their electrical properties, from thermoelectric and four point resistivity probes. The films’ surface morphology was investigated using a JEOL JM S-35 scanning electron microscope (SEM).
Results X-ray di~action, SEM and EPM4 analysis Figure 2 shows the X-ray diffraction pattern of CuInS, films sprayed with various Cu:In ionic ratios in the spraying mixture. The study of these diffractograms showed that all films were oriented with the (112) planes parallel to the substrate. The presence of the faint (103) line in the samples deposited with the Cu:In ratio equal to 1 and 1.3 confirms the chalcopyrite structure of these films. However, it appears that increasing the Cu:In up to 1.2 favours the formation of additional phases attributed to the Cu,S. SEM micrographs of sprayed CuInS, films are shown in Fig. 3. The cross-sectional photograph (Fig. 3(a)) indicates that the film is about 1 pm thick, as expected. The surface morphology changed by varying the copper to indium ratio (Fig. 3(b) and 3(c)). With an increasing copper content, the density of particles present on the film surfaces increases and the films become rough. Similar results have been reported previously by Padam and Rao [14]. The average grain size is around 50 nm, as has been reported by Rajaram et al. [15] with CuInS, sprayed onto a KC1 substrate. Table 1 shows the corrected results of the ionic ratio of the sprayed films. The Cu:In ratio is more than that in the starting solution and the sulphur content is less than that in the solution.
Optical transmission curves in the 400-2500 nm range were recorded at 300 K on a Beckman U.V. 5240 spectrophotometer. The transmission spectra for films deposited with various amounts of excess copper in the spray solution are shown in Fig. 4. The spectra display a single slope in the absorption edge region of 800-1000 nm. The absorption coefficients cr were calculated from these curves and were found to be about lo4 cm-’ near the band edge. Figure 5 shows plots of (&z#
662COS
n^
E Cdl”
: 1
8’ +
(cl Fig. 2. X-ray diffraction patterns of CuInSz thin films deposited at different Cu:In ratios in the initial spra:y solution: (a) 0.9:1; (b) 1:l and (c) 1.3:1 ratios.
26 TABLE 1. Composition
of the CuInS, films determined
Initial ratio Cu:In:S
Cu
In
0.8:1:3 0.9:1:3 1.0:1:3 1.1:1:3 1.2:1:3 1.3:1:3
26.1 f 1.5 28.2rt 1.5 29.6kO.8 31.5 f 1.5 36.7k1.5 39.7 + 1.5
27.1 f 25.6k 24.4 f 21.4+ 19.6& 18.7&
Composition
by EPMA
of the film (at.%)
1.5 1.5 1.2 1.5 1.0 1.5
S
Cu/In in the film
46.8 + 2.0 46.2 f 2.0 46.0 f 2.0 47.lk2.0 43.7 k2.0 41.6k2.0
0.96 1.10 1.21 1.47 1.87 2.12
(a) Cc) (d)
300
1300
800
1800
2300
h (nm)
Fig. 4. The transmission T as a function of wavelength A of CuInS, thin films deposited at: (a) 0.8:1; (b) 0.9:1; (c) 1:l; (d) 1.2:l and (e) 1.3:1 ratios in the initial spray solution.
.
(b) l
. II
(a)/ m
.
.
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.6
h v (eV) Fig. 5. (u&v)* versus hv for films deposited at: (a) 0.9:1; (b) 1:l and (c) 1.2:1 ratios in the initial spray solution.
Fig. 3. Cross-sectional micrograph (a) and surface micrographs of CuInS, thin films sprayed with: (b) 1.3:1 and (c) 1:l ratios.
than the 1.5 eV energy CuInS, [ 11.
reported
in the literature
for
against the photon energy hv. The band gaps of the films were determined by the extrapolation of the curves. The value for all films is around 1.45 eV, which is less
Electrical properties All the CuInS, films were p-type semiconductors as was observed by using the hot-probe method. Typical
27
TABLE 2. Electrical properties Cu:In ratios in the initial spray
Initial ratio Cu:In
Resistivity P (a
0.9:1 l.O:l l.l:l 1.2:1
63 2.0 6.0 x lo-* 2.8x10-*
cm)
for films solution
deposited
at different
Carrier cont. N,,, (cm-‘)
Mobility
3.8 2.7 1.8 9.0
2.6 11.6 5.8 2.5
x x x x
lOI 10” lOI 10’9
PP
(cm* V-’
s-l)
room temperature electrical resistivity variations with the excess copper in the spray solution are reported in Table 2. The p-type conductivity observed in CuInS, is governed by the cation vacancy or by the anion vacancy and cation interstitial [16]. The van der Pauw technique was used to evaluate the Hall effect measurements. The results are listed in Table 2. The details of measurements have been previously reported [17].
Conclusion
p-type CuInS, thin films with chalcopyrite structure were obtained using the spray solution method. The film sprayed with excess copper indicated the presence of another phase attributed to Cu,S. The Hall measurements show that the film sprayed with a Cu:In ratio equal to 1 presents a hole mobility in the order of 12 cm2 V-l ss’. This value is comparable to that obtained for the CuInS, single crystal [Ml.
References Ternary Chalcopyrite Semicon1 J. L. Shay and J. H. Wernic, ductors: Growth, Electronic Properties and Applications, Pergamon, New York, 1975, p. 110. and I>. R. Locker, Bull. 2 J. M. Messe, J. C. Manthuruthil Am. Phys. Sot., 20 (1975) 696. M. S. Ayyagari and G. A. Sanborn, J. Appl. 3 L. L. Kazmerski, Phys., 46 (1975) 4865. 4 H. L. Hwang, C. L. Cheng, L. M. Liu and C. Y. Sun, Thin Solid Films, 67 (1980) 83. 5 H. L. Hwang, C. C. Tu, J. S. Maa and C. Y. Sun, Sol. Enew Mater., 2 (1980) 433. 6 H. Neumann, W. Horig, B. Schumann, G. Kuhn, V. Savelev and J. Lagzdonis, Thin Solid Films, 79 (1981) 167. 7 H. L. Hwang, B. H. Tseng, C. Y. Sun and J. J. Loferski, Sol. Energy Mater., 4 (1980) 67. 8 S. P. Gindle, C. W. Smith and S. D. Mittlem, Appl. Phys. Lett., 35 (1) (1979) 24. 9 A. N. Tiwari, D. K. Pandya and K. L. Chopra, Thin Solid Films, 130 (1985) 217. M. Amlouk and R. Bennacer, Rev. Phys. Appl., 10 S. Belgacem, 25 (1990) 1213. 11 P. Rajaram, R. Thangaram, A. K. Sharma and 0. P. Agnihotri, Sol. Cells, 14 (1985) 123. 12 L. L. Kazmerski, F. R. White, G. A. Sanborn, A. J. Merill, M. S. Ayyagari, S. D. Mittleman and G. K. Morgan, Proc. 12th IEEE Conf: Photovoltaic Specialists Baton Rouge, LA, 1977, IEEE, New York 1977, p. 534. 13 L. L. Kazmerski, M. S. Ayyagari, G. A. Sanborn, F. R. White and A. J. Merill, Thin Solid Films, 41 (1977) 35. 14 G. D. Padam and S. U. M. Rao, Sol. Energy Mater., 13 (1986) 297. R. Thangaraj, A. K. Sharma, A. Raza and 0. 15 P. Rajaram, P. Agnihotri, Thin Solid Films, 100 (1983) 111. 16 B. R. Pamplin, Prog. Cryst. Growth Charact., 1 (1979) 331. 17 H. Bihri, C. Messaoudi, D. Sayah, A. Boyer, A. Mzerd.and M. Abd-Lefdil, Phys. Status Solidi (a), 129 (1992) 193. 18 B. Tell, J. L. Shay and H. M. Kasper, J. Appl. Phys., 43 (1972) 2469.
Materials Chemistry and Physics, 34 (1993) 24-27
Structural H. Bihri,
and optical properties
C. Messaoudi,
D. Sayah,
of sprayed CuInS, thin films
M. Abd-Lefdil
Physics Department, Faculty of Sciences, Universite’ Mohamme4
Rabat (Morocco)
and M. Cad&e Laboratoire d’lnfrarouge, Universitk des Sciences et Techniques du Languedoc, Place Eugkne Bataillon, 34095 Montpellier (France) Presented at the 3rd Meeting on the Science of Materials, 27th-29th October 1991, Oran (Algeria) (Received
February
26, 1992; accepted
July 29, 1992)
Abstract p-type CuInSz thin films of about 1 pm were prepared by the spray pyrolysis method. The Cu:In ratios in the spray solution was varied in order to produce good quality single phase CuInSr films. X-ray analysis showed that the film sprayed with a Cu:In ratio equal to 1 in the spraying mixture presented a single phase CuInS, with a chalcopyrite structure, and oriented preferentially with (112) planes parallel to the substrate. The surface morphology of the deposited films changed with the copper content. The optical band gap at room temperature was around 1.45 eV. The Hall effect measurements were studied.
Introduction
Experimental
CuInS, ternary semiconductors have been extensively studied in recent years because of their promising applications especially for the photovoltaic conversion. The direct band gap of about 1.5 eV [l] is close to the optimum value for solar energy conversion. CuInS, can be synthesised in both n- and p-type semiconductors. Its homojunction has been predicted to yield a theoretical efficiency of 27-32% [2]. Several techniques have been reported for the preparation of thin CuInS, films, namely single and doublesource evaporation [3], r.f. sputtering [4], flash evaporation [5, 61, chemical vapour deposition [7, 81 and spray pyrolysis [9, lo]. A thin film solar cell totally sprayed with CuInS,/Cd(Zn)S with an efficiency of 2.6% has been described by Rajaram et al. [ll]. Kazmerski et al. [12] have reported an efficiency of 3.6% for CuInSJCdS using CuInS, prepared by means of double-source evaporation. It has also been reported that single-source evaporation does not produce good quality single phase CuInS, films [13]. For large scale production only spray pyrolysis and sulphurization of CuIn layers seem to be useful. The purpose of this work is to report the physical characteristics of sprayed CuInS, thin films, prepared by varying the copper to indium ratio in the starting spray solution.
A starting solution containing the desired cations with sulphur, indium and copper respectively in the form of thiourea, indium trichloride and cuprous chloride at a concentration of 0.005 M was used. This starting solution was sprayed in a fine mist on to clean glass substrates heated to 570-670 K. A schematic diagram of our set-up is shown in Fig. 1.
0254-0584/93/$6.00
2
8T 1
+I
+3-
d
5
6
7
: Fig. 1. A schematic of the chemical spraying set-up. 1, Spraying solution; 2, pump flowmeter; 3, nozzle waggon; 4, air pump; 5, nozzle; 6, aspiration chamber; 7, glass substrates; 8, hot plate; 9, temperature controller.
0 1993 - Elsevier Sequoia. All rights reserved
A preliminary investigation showed that good and reproducible films could be obtained using a spray-rate of 5 cc min-l and a substrate temperature of around 620 K. This would yield a deposition rate about 50 nm min-I. For the purpose of studying the effect of the copper to indium ratio, the films had been deposited with Cu:In ratio in the 0.8-1.3 range. The structure of the thin films of CuInS, was determined from X-ray diffraction; their composition by the electron probe micro-analysis (EPMA), and their electrical properties, from thermoelectric and four point resistivity probes. The films’ surface morphology was investigated using a JEOL JM S-35 scanning electron microscope (SEM).
Results X-ray di~action, SEM and EPM4 analysis Figure 2 shows the X-ray diffraction pattern of CuInS, films sprayed with various Cu:In ionic ratios in the spraying mixture. The study of these diffractograms showed that all films were oriented with the (112) planes parallel to the substrate. The presence of the faint (103) line in the samples deposited with the Cu:In ratio equal to 1 and 1.3 confirms the chalcopyrite structure of these films. However, it appears that increasing the Cu:In up to 1.2 favours the formation of additional phases attributed to the Cu,S. SEM micrographs of sprayed CuInS, films are shown in Fig. 3. The cross-sectional photograph (Fig. 3(a)) indicates that the film is about 1 pm thick, as expected. The surface morphology changed by varying the copper to indium ratio (Fig. 3(b) and 3(c)). With an increasing copper content, the density of particles present on the film surfaces increases and the films become rough. Similar results have been reported previously by Padam and Rao [14]. The average grain size is around 50 nm, as has been reported by Rajaram et al. [15] with CuInS, sprayed onto a KC1 substrate. Table 1 shows the corrected results of the ionic ratio of the sprayed films. The Cu:In ratio is more than that in the starting solution and the sulphur content is less than that in the solution.
Optical transmission curves in the 400-2500 nm range were recorded at 300 K on a Beckman U.V. 5240 spectrophotometer. The transmission spectra for films deposited with various amounts of excess copper in the spray solution are shown in Fig. 4. The spectra display a single slope in the absorption edge region of 800-1000 nm. The absorption coefficients cr were calculated from these curves and were found to be about lo4 cm-’ near the band edge. Figure 5 shows plots of (&z#
662COS
n^
E Cdl”
: 1
8’ +
(cl Fig. 2. X-ray diffraction patterns of CuInSz thin films deposited at different Cu:In ratios in the initial spra:y solution: (a) 0.9:1; (b) 1:l and (c) 1.3:1 ratios.
26 TABLE 1. Composition
of the CuInS, films determined
Initial ratio Cu:In:S
Cu
In
0.8:1:3 0.9:1:3 1.0:1:3 1.1:1:3 1.2:1:3 1.3:1:3
26.1 f 1.5 28.2rt 1.5 29.6kO.8 31.5 f 1.5 36.7k1.5 39.7 + 1.5
27.1 f 25.6k 24.4 f 21.4+ 19.6& 18.7&
Composition
by EPMA
of the film (at.%)
1.5 1.5 1.2 1.5 1.0 1.5
S
Cu/In in the film
46.8 + 2.0 46.2 f 2.0 46.0 f 2.0 47.lk2.0 43.7 k2.0 41.6k2.0
0.96 1.10 1.21 1.47 1.87 2.12
(a) Cc) (d)
300
1300
800
1800
2300
h (nm)
Fig. 4. The transmission T as a function of wavelength A of CuInS, thin films deposited at: (a) 0.8:1; (b) 0.9:1; (c) 1:l; (d) 1.2:l and (e) 1.3:1 ratios in the initial spray solution.
.
(b) l
. II
(a)/ m
.
.
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.6
h v (eV) Fig. 5. (u&v)* versus hv for films deposited at: (a) 0.9:1; (b) 1:l and (c) 1.2:1 ratios in the initial spray solution.
Fig. 3. Cross-sectional micrograph (a) and surface micrographs of CuInS, thin films sprayed with: (b) 1.3:1 and (c) 1:l ratios.
than the 1.5 eV energy CuInS, [ 11.
reported
in the literature
for
against the photon energy hv. The band gaps of the films were determined by the extrapolation of the curves. The value for all films is around 1.45 eV, which is less
Electrical properties All the CuInS, films were p-type semiconductors as was observed by using the hot-probe method. Typical
27
TABLE 2. Electrical properties Cu:In ratios in the initial spray
Initial ratio Cu:In
Resistivity P (a
0.9:1 l.O:l l.l:l 1.2:1
63 2.0 6.0 x lo-* 2.8x10-*
cm)
for films solution
deposited
at different
Carrier cont. N,,, (cm-‘)
Mobility
3.8 2.7 1.8 9.0
2.6 11.6 5.8 2.5
x x x x
lOI 10” lOI 10’9
PP
(cm* V-’
s-l)
room temperature electrical resistivity variations with the excess copper in the spray solution are reported in Table 2. The p-type conductivity observed in CuInS, is governed by the cation vacancy or by the anion vacancy and cation interstitial [16]. The van der Pauw technique was used to evaluate the Hall effect measurements. The results are listed in Table 2. The details of measurements have been previously reported [17].
Conclusion
p-type CuInS, thin films with chalcopyrite structure were obtained using the spray solution method. The film sprayed with excess copper indicated the presence of another phase attributed to Cu,S. The Hall measurements show that the film sprayed with a Cu:In ratio equal to 1 presents a hole mobility in the order of 12 cm2 V-l ss’. This value is comparable to that obtained for the CuInS, single crystal [Ml.
References Ternary Chalcopyrite Semicon1 J. L. Shay and J. H. Wernic, ductors: Growth, Electronic Properties and Applications, Pergamon, New York, 1975, p. 110. and I>. R. Locker, Bull. 2 J. M. Messe, J. C. Manthuruthil Am. Phys. Sot., 20 (1975) 696. M. S. Ayyagari and G. A. Sanborn, J. Appl. 3 L. L. Kazmerski, Phys., 46 (1975) 4865. 4 H. L. Hwang, C. L. Cheng, L. M. Liu and C. Y. Sun, Thin Solid Films, 67 (1980) 83. 5 H. L. Hwang, C. C. Tu, J. S. Maa and C. Y. Sun, Sol. Enew Mater., 2 (1980) 433. 6 H. Neumann, W. Horig, B. Schumann, G. Kuhn, V. Savelev and J. Lagzdonis, Thin Solid Films, 79 (1981) 167. 7 H. L. Hwang, B. H. Tseng, C. Y. Sun and J. J. Loferski, Sol. Energy Mater., 4 (1980) 67. 8 S. P. Gindle, C. W. Smith and S. D. Mittlem, Appl. Phys. Lett., 35 (1) (1979) 24. 9 A. N. Tiwari, D. K. Pandya and K. L. Chopra, Thin Solid Films, 130 (1985) 217. M. Amlouk and R. Bennacer, Rev. Phys. Appl., 10 S. Belgacem, 25 (1990) 1213. 11 P. Rajaram, R. Thangaram, A. K. Sharma and 0. P. Agnihotri, Sol. Cells, 14 (1985) 123. 12 L. L. Kazmerski, F. R. White, G. A. Sanborn, A. J. Merill, M. S. Ayyagari, S. D. Mittleman and G. K. Morgan, Proc. 12th IEEE Conf: Photovoltaic Specialists Baton Rouge, LA, 1977, IEEE, New York 1977, p. 534. 13 L. L. Kazmerski, M. S. Ayyagari, G. A. Sanborn, F. R. White and A. J. Merill, Thin Solid Films, 41 (1977) 35. 14 G. D. Padam and S. U. M. Rao, Sol. Energy Mater., 13 (1986) 297. R. Thangaraj, A. K. Sharma, A. Raza and 0. 15 P. Rajaram, P. Agnihotri, Thin Solid Films, 100 (1983) 111. 16 B. R. Pamplin, Prog. Cryst. Growth Charact., 1 (1979) 331. 17 H. Bihri, C. Messaoudi, D. Sayah, A. Boyer, A. Mzerd.and M. Abd-Lefdil, Phys. Status Solidi (a), 129 (1992) 193. 18 B. Tell, J. L. Shay and H. M. Kasper, J. Appl. Phys., 43 (1972) 2469.