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Preparation of In2O3:F thin films grown by spray pyrolysis technique
Renewable Energy 29 (2004) 1665–1669 www.elsevier.com/locate/renene
Preparation of In2O3:F thin films grown by spray pyrolysis technique S.M. Rozati , T. Ganj Physics Department, The University of Guilan, Rasht 41335, Iran Received 1 August 2003; accepted 19 January 2004
Abstract Transparent conducting fluorine doped indium oxide (In2O3:F) thin films have been deposited on Corning 7059 glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. The X-ray diffraction pattern of the films deposited at lower substrate temperav ture (Ts ¼ 300 C) showed no peaks of In2O3:F. In the useful range for deposition (i.e. 425– v 600 C), the orientation of the films was predominantly [400]. For the 4500 G thick In2O3:F deposited with an F content of 10-wt%, the minimum sheet resistance was 120 X and average transmission in the visible wavelength rang (400–700 nm) was 88%. # 2004 Elsevier Ltd. All rights reserved. Keywords: In2O3:F; Spray pyrolysis; Transparent-conducting oxide
1. Introduction In recent years, there has considerable interest in transparent and conducting oxides because of their many industrial applications [1–5]. Thin films of these materials can be produced by various techniques and are called transparent conducting oxides (TCO) [6–9]. They possess a high transparency for visible radiation and also high electrical conductivity [10]. Transparent conducting oxides are normally n-type semiconductors. The high transparency for the visible light and infrared radiation in these films are due to the moderately high carrier concentration of free electrons and sufficiently wide band gap (greater than 3 eV) [11,12]. The purpose of
Corresponding author. fax: + 89-131-322-0066. E-mail address: [email protected] (S.M. Rozati).
0960-1481/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2004.01.007
1666
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the present work is to produce and investigate thin In2O3:F films which have repeatable electrical properties and good adhesion of the film to substrate for liquid crystal display devices [13].
2. Experimental The spray pyrolysis apparatus used in this work consists of a home made spraying unit, substrate holder with heater, and enclosure. The glass substrate is kept on a stainless steel (ss) plate (17 17 2 cm) that is heated by a 3 kW heater using canthal-heating coil. The heater is capable of heating the substrate up to a v temperature of 700 C. The temperature of the substrate is controlled by using a temperature controller and a Chromel-Alomel thermocouple kept at the center of the ss plate. The carrier gas used in all the experiments was air, which is supplied from an air compressor. The air produced by the compressor was first filtered and then connected to the glass spray-gun (atomizer) through a flow meter for controlling its flow. The custom glass spray gun, having a nozzle diameter of 0.2 mm, was positioned at a distance of 30 cm above the substrate. The whole assembly is kept in an enclosure connected to an exhaust. The structural, electrical, and optical properties of TCOs are strongly affected by the temperature of substrate. The optical transmission was evaluated using a uvvisible spectrophotometer (UV/VIS-2100 Shimadzu). X-ray diffraction (XRD) (Philips-pw-1830) was used to characterize the crystal structure of the films. The thickness of the films can be calculated by using an interference pattern observed in the visible region following the formula given by Manifacier [14].
3. Results and discussion In the spray pyrolysis technique, a solution containing soluble salts of the constituent atoms of the desired mineral compound such as indium chloride (In Cl3) dissolved in a solution of water and alcohol is atomized into a heated glass substrate with the aid of a carrier gas through a heterogeneous reaction. A metal oxide is formed on the substrate. For depositing fluorine doped indium oxide films, an aerosol solution prepared from a solution of ammonium fluoride was added to the solution of InCl3. In2O3:F (F=In ¼ 10wt%) thin films were deposited on Corning 7059 glass subv strate at different substrate temperature ranging from 300 to 600 C at an interval v of 50 C keeping all other parameters constant (i.e. air flow rate 6 l/min (l pm), distance between substrate to nozzle Dsn ¼ 30 cm and solution composition). Substrate temperature is an important parameter for spray pyrolysis deposition. v It is observed that at lower substrate temperature (less than 250 C), the growth
S.M. Rozati, T. Ganj / Renewable Energy 29 (2004) 1665–1669
1667
Fig. 1. X-ray diffraction patterns of In2O3 thin films deposited at various substrate temperatures.
rate is controlled by activated processes. At higher substrate temperature (greater v than 550 C), the size of the droplet decreases appreciably due to the evaporation of water molecules, resulting In a homogeneous reaction, the reaction may be completed above the substrate, leading to powder formation. Hence, very low and very high temperatures are not suitable for preparation of these TCOs. Results of X-ray diffraction analysis revealed that the film prepared at substrate v temperature less than 300 C gave no observed diffraction peaks (Fig. 1a) (amorphous) and become polycrystalline when deposited at higher temperature (Fig. 1b–f). This crystalline structure was based on one peak (400) corresponding to the cubic structure for In2O3. The sheet resistance of In2O3:F coating is shown as a function of the substrate temperature in Fig. 2. The sheet resistance decreases with increased substrate temperature, and values as low as Rsh ¼ 120 X are reached for substrate temperatures v of 425 C. This enables us to obtain the maximum transmission and minimum
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Fig. 2. Variation of sheet resistance with substrate temperature for In2O3:F films deposited at different substrate temperatures.
sheet resistance for a given In2O3:F films by adjusting the substrate temperature. Similar results for the dependence of resistance on substrate temperature have been obtained in [15] for deposition of In2O3 films doped with 10-wt% ZrO2. Fig. 3 shows a typical curve of transmission (at wavelength 550 nm) versus substrate temperature of a series of In2O3:F thin films. Films deposited at lower subv strate temperature (less than 350 C) exhibited a dark milky appearance due to the low wavelength absorption at a low-temperature deposition. The optical properties of the films changed significantly by increasing substrate temperature from 400 to v 600 C. In the case of higher substrate temperature, the appropriate amount of reduced oxides necessary to exhibit good transparency and low sheet resistance are incorporated into the grown crystals.
Fig. 3. Variation of visible transmission with substrate temperature for In2O3:F films deposited at different substrate temperatures.
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4. Summary We have outlined a simple procedure for coating In2O3:F transparent conducting coating. The XRD results reveal that the predominant orientation of the film is [400]. The sheet resistance of the films decreases with increasing the substrate temv perature and become minimum at Ts ¼ 425 C. It is also observed that the visible transmission of the film improves as the deposition temperature is increased and saturates at higher temperature. Acknowledgements This work was supported by the department of research of the University of Guilan. The authors are grateful to Professor Zanjanchi, Head of the Higher Education Department for using X-ray systems. References [1] Coutts TJ, Young DL, Li X. MRS Bull 2000;25:56. [2] Coutts TJ, Mason TO, Perkins JD, Ginley DS. Proceedings of the Int. Symposium on Photovoltaic for the 21st Century, USA, 1999:99;274. [3] Coutts TJ, Young DL, Li X, Mulligan WP, Wu X. J Vac Sci Technol A Vac Surf Films 2000; 18:2646. [4] Sohn MH, Kim D, Kim SJ, Paik NW, Gupta S. J Vac Sci Technol A 2003;21:1347. [5] Biyikli N, Kartgoglu T, Aytur O, Kimukin I, Ozbay E. Appl Phys Lett 2001;79:2838. [6] Bel R, Tahar H, Ban T, Ohaya Y, Takahashi Y. J Appl Phys 1997;82:865. [7] Sohan MH, Kim D, Kim SJ, Paik NW. J Vac Sci Technol A 2003;21:1347. [8] Li X, Young DL, Moutinho H, Yan Y, Narayanswamy C, Gessert TA, Coutts TJ. Electroch SolidState Lett 2001;4:43. [9] Cho JS, Yoon KH, Koh SK. J Appl Phys 2001;89:3223. [10] Hartnagel H, Dawar AL, Jain AK, Jagadish C. Semiconducting transparent thin films. Institute of Physics Publishing Bristol and Philadelphia; 1995. [11] Hamberg I, Granqvist CG. J Appl Phys 1986;60:R123. [12] Chopra KL, Major S, Pandya DK. Thin Solid Films 1983;102:1. [13] Ghanadzadeh A, Zanjanchi MA. Spectrochimica Acta 2001;57/9A:1865. [14] Manifacier JC, Fillard JP, Bind JM. Thin Solid Films 1981;77:67. [15] Qadri SB, Kim H, Khan HR, Pique A, Horwitz JS, Chrisey D, Kim WJ, Skerton EF. Thin Solid Films 2000;377:750.
Preparation of In2O3:F thin films grown by spray pyrolysis technique S.M. Rozati , T. Ganj Physics Department, The University of Guilan, Rasht 41335, Iran Received 1 August 2003; accepted 19 January 2004
Abstract Transparent conducting fluorine doped indium oxide (In2O3:F) thin films have been deposited on Corning 7059 glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. The X-ray diffraction pattern of the films deposited at lower substrate temperav ture (Ts ¼ 300 C) showed no peaks of In2O3:F. In the useful range for deposition (i.e. 425– v 600 C), the orientation of the films was predominantly [400]. For the 4500 G thick In2O3:F deposited with an F content of 10-wt%, the minimum sheet resistance was 120 X and average transmission in the visible wavelength rang (400–700 nm) was 88%. # 2004 Elsevier Ltd. All rights reserved. Keywords: In2O3:F; Spray pyrolysis; Transparent-conducting oxide
1. Introduction In recent years, there has considerable interest in transparent and conducting oxides because of their many industrial applications [1–5]. Thin films of these materials can be produced by various techniques and are called transparent conducting oxides (TCO) [6–9]. They possess a high transparency for visible radiation and also high electrical conductivity [10]. Transparent conducting oxides are normally n-type semiconductors. The high transparency for the visible light and infrared radiation in these films are due to the moderately high carrier concentration of free electrons and sufficiently wide band gap (greater than 3 eV) [11,12]. The purpose of
Corresponding author. fax: + 89-131-322-0066. E-mail address: [email protected] (S.M. Rozati).
0960-1481/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2004.01.007
1666
S.M. Rozati, T. Ganj / Renewable Energy 29 (2004) 1665–1669
the present work is to produce and investigate thin In2O3:F films which have repeatable electrical properties and good adhesion of the film to substrate for liquid crystal display devices [13].
2. Experimental The spray pyrolysis apparatus used in this work consists of a home made spraying unit, substrate holder with heater, and enclosure. The glass substrate is kept on a stainless steel (ss) plate (17 17 2 cm) that is heated by a 3 kW heater using canthal-heating coil. The heater is capable of heating the substrate up to a v temperature of 700 C. The temperature of the substrate is controlled by using a temperature controller and a Chromel-Alomel thermocouple kept at the center of the ss plate. The carrier gas used in all the experiments was air, which is supplied from an air compressor. The air produced by the compressor was first filtered and then connected to the glass spray-gun (atomizer) through a flow meter for controlling its flow. The custom glass spray gun, having a nozzle diameter of 0.2 mm, was positioned at a distance of 30 cm above the substrate. The whole assembly is kept in an enclosure connected to an exhaust. The structural, electrical, and optical properties of TCOs are strongly affected by the temperature of substrate. The optical transmission was evaluated using a uvvisible spectrophotometer (UV/VIS-2100 Shimadzu). X-ray diffraction (XRD) (Philips-pw-1830) was used to characterize the crystal structure of the films. The thickness of the films can be calculated by using an interference pattern observed in the visible region following the formula given by Manifacier [14].
3. Results and discussion In the spray pyrolysis technique, a solution containing soluble salts of the constituent atoms of the desired mineral compound such as indium chloride (In Cl3) dissolved in a solution of water and alcohol is atomized into a heated glass substrate with the aid of a carrier gas through a heterogeneous reaction. A metal oxide is formed on the substrate. For depositing fluorine doped indium oxide films, an aerosol solution prepared from a solution of ammonium fluoride was added to the solution of InCl3. In2O3:F (F=In ¼ 10wt%) thin films were deposited on Corning 7059 glass subv strate at different substrate temperature ranging from 300 to 600 C at an interval v of 50 C keeping all other parameters constant (i.e. air flow rate 6 l/min (l pm), distance between substrate to nozzle Dsn ¼ 30 cm and solution composition). Substrate temperature is an important parameter for spray pyrolysis deposition. v It is observed that at lower substrate temperature (less than 250 C), the growth
S.M. Rozati, T. Ganj / Renewable Energy 29 (2004) 1665–1669
1667
Fig. 1. X-ray diffraction patterns of In2O3 thin films deposited at various substrate temperatures.
rate is controlled by activated processes. At higher substrate temperature (greater v than 550 C), the size of the droplet decreases appreciably due to the evaporation of water molecules, resulting In a homogeneous reaction, the reaction may be completed above the substrate, leading to powder formation. Hence, very low and very high temperatures are not suitable for preparation of these TCOs. Results of X-ray diffraction analysis revealed that the film prepared at substrate v temperature less than 300 C gave no observed diffraction peaks (Fig. 1a) (amorphous) and become polycrystalline when deposited at higher temperature (Fig. 1b–f). This crystalline structure was based on one peak (400) corresponding to the cubic structure for In2O3. The sheet resistance of In2O3:F coating is shown as a function of the substrate temperature in Fig. 2. The sheet resistance decreases with increased substrate temperature, and values as low as Rsh ¼ 120 X are reached for substrate temperatures v of 425 C. This enables us to obtain the maximum transmission and minimum
1668
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Fig. 2. Variation of sheet resistance with substrate temperature for In2O3:F films deposited at different substrate temperatures.
sheet resistance for a given In2O3:F films by adjusting the substrate temperature. Similar results for the dependence of resistance on substrate temperature have been obtained in [15] for deposition of In2O3 films doped with 10-wt% ZrO2. Fig. 3 shows a typical curve of transmission (at wavelength 550 nm) versus substrate temperature of a series of In2O3:F thin films. Films deposited at lower subv strate temperature (less than 350 C) exhibited a dark milky appearance due to the low wavelength absorption at a low-temperature deposition. The optical properties of the films changed significantly by increasing substrate temperature from 400 to v 600 C. In the case of higher substrate temperature, the appropriate amount of reduced oxides necessary to exhibit good transparency and low sheet resistance are incorporated into the grown crystals.
Fig. 3. Variation of visible transmission with substrate temperature for In2O3:F films deposited at different substrate temperatures.
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4. Summary We have outlined a simple procedure for coating In2O3:F transparent conducting coating. The XRD results reveal that the predominant orientation of the film is [400]. The sheet resistance of the films decreases with increasing the substrate temv perature and become minimum at Ts ¼ 425 C. It is also observed that the visible transmission of the film improves as the deposition temperature is increased and saturates at higher temperature. Acknowledgements This work was supported by the department of research of the University of Guilan. The authors are grateful to Professor Zanjanchi, Head of the Higher Education Department for using X-ray systems. References [1] Coutts TJ, Young DL, Li X. MRS Bull 2000;25:56. [2] Coutts TJ, Mason TO, Perkins JD, Ginley DS. Proceedings of the Int. Symposium on Photovoltaic for the 21st Century, USA, 1999:99;274. [3] Coutts TJ, Young DL, Li X, Mulligan WP, Wu X. J Vac Sci Technol A Vac Surf Films 2000; 18:2646. [4] Sohn MH, Kim D, Kim SJ, Paik NW, Gupta S. J Vac Sci Technol A 2003;21:1347. [5] Biyikli N, Kartgoglu T, Aytur O, Kimukin I, Ozbay E. Appl Phys Lett 2001;79:2838. [6] Bel R, Tahar H, Ban T, Ohaya Y, Takahashi Y. J Appl Phys 1997;82:865. [7] Sohan MH, Kim D, Kim SJ, Paik NW. J Vac Sci Technol A 2003;21:1347. [8] Li X, Young DL, Moutinho H, Yan Y, Narayanswamy C, Gessert TA, Coutts TJ. Electroch SolidState Lett 2001;4:43. [9] Cho JS, Yoon KH, Koh SK. J Appl Phys 2001;89:3223. [10] Hartnagel H, Dawar AL, Jain AK, Jagadish C. Semiconducting transparent thin films. Institute of Physics Publishing Bristol and Philadelphia; 1995. [11] Hamberg I, Granqvist CG. J Appl Phys 1986;60:R123. [12] Chopra KL, Major S, Pandya DK. Thin Solid Films 1983;102:1. [13] Ghanadzadeh A, Zanjanchi MA. Spectrochimica Acta 2001;57/9A:1865. [14] Manifacier JC, Fillard JP, Bind JM. Thin Solid Films 1981;77:67. [15] Qadri SB, Kim H, Khan HR, Pique A, Horwitz JS, Chrisey D, Kim WJ, Skerton EF. Thin Solid Films 2000;377:750.