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A deep understanding of relationship between reverse time and growth of ITO film deposited by direct current pulsed sputtering
Accepted Manuscript A deep understanding of relationship between reverse time and growth of ITO film deposited by direct current pulsed sputtering Weichao Chen, Haoting Sun, Hualin Wang, Weiwei Jiang, Shimin Liu, Chaoqian Liu, Nan Wang, Yunxian Cui, Weiping Chai, Wanyu Ding, Bing Han PII: DOI: Reference:
S0167-577X(18)30343-4 https://doi.org/10.1016/j.matlet.2018.02.129 MLBLUE 23955
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
11 December 2017 27 January 2018 27 February 2018
Please cite this article as: W. Chen, H. Sun, H. Wang, W. Jiang, S. Liu, C. Liu, N. Wang, Y. Cui, W. Chai, W. Ding, B. Han, A deep understanding of relationship between reverse time and growth of ITO film deposited by direct current pulsed sputtering, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.02.129
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A deep understanding of relationship between reverse time and growth of ITO film deposited by direct current pulsed sputtering Weichao Chena, Haoting Suna, Hualin Wanga, Weiwei Jianga, Shimin Liua, Chaoqian Liua, Nan Wanga, Yunxian Cuia, Weiping Chaia, Wanyu Dinga,1, Bing Hanb,2 a
b
Dalian Jiaotong University, Dalian 116028, China.
Liaoning Province Key Laboratory of Metallurgical Equipment and Process Control, University of Science and Technology Liaoning, Anshan 114051, China.
Abstract: Indium tin oxide (ITO) film was deposited by the traditional direct current (DC) pulsed magnetron sputtering technology. With the increase of reverse time from 0 to 4.0 μs, the crystal structure of ITO film changed from the polycrystalline structure without preferred orientation to (100) preferred orientation. ITO film with (100) preferred orientation showed the satisfactory optical and electrical properties, such as the band gap in 4.15 eV and carrier concentration in 4.25×1020/cm3. Based on DC pulsed voltage waveform, the formation of (100) preferred orientation, as well as the change of optical and electrical properties of ITO film, were analyzed logically. Keywords: Indium tin oxide; Thin films; Sputtering; Reverse time; Preferred orientation; Optical and electrical property 1. Introduction Indium tin oxide (ITO) film has been widely employed in the photo-electric and electro-optical conversion fields, which was mainly used as the transparent conductive electrode [1-3]. In the industry fields, ITO film was mainly prepared by 1
2
Co-Corresponding author: Dr./Prof. Wanyu Ding E-mail: [email protected] and [email protected] Address: College of Materials Science and Engineering, Dalian Jiaotong University, No. 794 Huanghe Road, Shahekou District, Dalian, Liaoning Province/116028, China. Co-Corresponding author: Dr./Prof. Bing Han E-mail: [email protected] and [email protected] Address: College of Mechanical Engineering & Automation, University of Science and Technology Liaoning, No. 185 Qianshanzhong Road, Qianshan District, Anshan, Liaoning Province/114051, China.
1
the sputtering technology, such as direct current (DC), radio frequency, medium frequency, and so on [4-6]. Now, ITO film could also be prepared by DC pulsed sputtering, which had the advantage of high sputtering efficiency [7]. The growth model of ITO film was strongly influenced by DC pulsed sputtering parameters, such as power density, frequency, especially for reverse time. In turn, the crystal structure and optical-electrical properties of ITO film could be strongly influenced by the reverse time. But, the sputtering mechanism behind different reverse time was still not deeply understood. In our experiment, ITO films were deposited by DC pulsed magnetron sputtering technology. The aim is to deeply understand the relationship between reverse time, preferred orientation, and optical-electrical properties of ITO film, as well as the physicochemical mechanism behind them. 2. Experimental ITO film was deposited onto the quartz substrate, which was sputtered from ITO target by pure Ar gas. The sputtering power was supplied by Pinnacle™ Plus+ 5 kW DC pulsed power supply unit. DC pulsed sputtering power and pulse frequency was kept at 600 W and 100 kHz, respectively. The reverse time was adjusted from 0 to 4.0 μs. The crystal structure, electrical, and optical property of ITO film was analyzed by PANalytical Empyrean X-ray diffraction (XRD) system, Hall 8800 system, and U-3310 UV spectrophotometer, respectively. Based on Tauc relationship, the band gap of ITO film could be deduced [8, 9]. Because the sputtering process was carried out by pure Ar gas, the composition and chemical bond structure of ITO film was same for all reverse time [10]. The thickness of ITO film was kept at 301.4±5.5 nm for all reverse time. In turn, the growth rate of ITO film could be deduced. During the sputtering process, the sputtering voltage waveform of pulsed power supply unit was recorded by Tektronix TDS 2022B oscilloscope. The detailed deposition parameters
2
and measurement information could be found in Supplementary. 3. Results and discussion The crystal structure of ITO film was shown in Fig. 1. From Fig. 1, it can be seen clearly that all XRD patterns displayed the diffraction peaks attributed to cubic ferrite In2O3 (222) and (400) phase, respectively [11-13]. It can be found that all diffraction peaks shifted toward the small angle, which was explained in Supplementary. While, the most important feature of Fig. 1 was that with the increase of reverse time from 0 to 4.0 μs, the relative intensity of (222) and (400) peak gradually became weaker and stronger, respectively. Especially for ITO film with reverse time in 4.0 μs, (400) peak became the main one, which meant ITO film with (100) preferred orientation.
Fig. 1. XRD patterns of ITO films deposited with different reverse time. Hall measurement results showed that the resistivity was kept at 6.16±0.29×10-4 Ω·cm for all ITO films. In general, because of almost constant resistivity, perhaps the conclusion was drawn that the reverse time had no influence on the properties of ITO film. In order to deeply understand the relationship between reverse time and properties of ITO film, the relevant measurement results were shown in Fig. 2. From Fig. 2, it can be seen that with the increase of reverse time from 0 to 4.0 μs, the growth rate, band gap, and carrier concentration increased from 1.12 to 1.85 nm/s, 3.92 to 4.15 eV, and 2.93 to 4.25×1020/cm3, respectively. On the contrary, the carrier mobility decreased from 31.58 to 23.89 cm2/Vs. Combining the results in Fig. 1 and 2, it can be found that the reverse time had a strong influence on the crystal structure, growth rate, optical, and electrical properties of ITO film.
3
Fig. 2. The growth rate, band gap, concentration, and mobility of ITO film deposited with different reverse time. In order to deeply understand the sputtering process, DC pulsed voltage waveform was recorded, just as shown in Fig. 3 (a). One pulsed period could be divided into Region 1, 2, and 3, which was the reverse time, high power time, and low power time respectively, just as shown in Fig. 3 (b). The calculation result showed that the sum work in Region 1, 2, and 3 was almost same for all reverse time. Besides, the work in Region 1 could be negligible for all reverse time. So only sum work in Region 2 and 3 was considered, which really contributed to the sputtering process. Then, the average power in Region 2 and 3 could be theoretically calculated and actually measured, which corresponded well each other, just as shown in Fig. 4 (a). Based on the result in Fig. 4 (a), the equivalent power arrangement for different reverse time was shown in Fig. 4 (b). The details of measured and calculated work/power could be found in Supplementary. From Fig. 4 (b), it can be found that with the increase of reverse time, the average power in Region 2 increased gradually, except a little decrease for reverse time of 4.0 μs.
Fig. 3. DC pulse voltage waveform with different reverse time (a). The diagram of dividing DC pulse voltage waveform (b).
4
Fig. 4. The calculated and measured power with different reverse time (a), which Pr, Pa, T, and R was the average power in Region 2 and 3, average power in one period, period, and reverse time, respectively. The equivalent power arrangement for different reverse time (b). Based on the analysis of DC pulse sputtering process in Fig. 3 and 4, the change in Fig. 1 and 2 could be logically discussed. Firstly, in case of DC sputtering process, the sputtering power was fixed at lower value, which resulted in the incident In, Sn, and O atom/ion without kinetic energy higher enough and all kinetic energy was lost as the heat through inelastic collision. Besides, based on the plasma theory [14, 15], the mean free path of 0.6 Pa was about 100-101 cm, which was similar to the distance between target and substrate. So it was hard for In, Sn, and O atom/ion in plasma to collide each other. So In, Sn, and O atom/ion in plasma was incident onto the growth surface of ITO film, directly. Combining above reasons, the incident In, Sn, and O atom/ion was located at ITO film growth surface randomly, which resulted in the random chemical bond and random crystal growth direction. So in case of DC sputtering process, XRD pattern displayed no preferred orientation. Secondly, with the increase of reverse time, the sputtering process began with the high power, and ended with the low power. In high power sputtering process, In, Sn, and O atom/ion contented the higher kinetic energy. In this situation, these particles arrived at ITO film growth surface with kinetic energy higher enough, which couldn’t be totally lost as the heat through inelastic collision. So part of kinetic energy was transformed as the crystal energy in ITO crystal lattices, which could result in the growth of ITO grains along the certain direction. Besides, based on the film growth
5
ratio, the sputtering yield in high power part was much higher than that in low power part, which in turn decreased the mean free path at high power part. So one reasonable hypothesis should be considered, which was the reactive collision between In, Sn, and O atom/ion in plasma. Except the elastic/inelastic collision between In, Sn, and O atom/ion in plasma, the reactive collision between them could chemically product In-O/Sn-O groups, which was the key point in our experiment. For the growth surface of ITO film, the incident In-O/Sn-O groups also arranged themselves at the positions with lowest energy, which resulted in the formation of columnar grain along the normal direction of ITO film surface [16]. The detailed results and discussion about formation of columnar grain were shown in Supplementary. Combining above reasons, with the increase of reverse time, the value of high power increased, which resulted in more columnar grains appeared in ITO film. In turn, with the increase of reverse time, ITO film displayed more obvious (100) preferred orientation, just as shown in Fig. 1. Above analysis indicated that the high power sputtering process influenced ITO grain growth models, obviously. Based on the different ITO grain growth models, the change of optical and electrical properties of ITO film in Fig. 2 could be deeply understood. With the increase of reverse time, ITO grain growth mode changed from the equiaxed grain to columnar grain, which could improve the band gap and carrier concentration. On the contrary, the grain boundary between columnar had a little influence to the carrier mobility. The detailed discussion could be found in Supplementary. 4. Conclusions In summary, the traditional direct current pulsed magnetron sputtering technology was employed to prepare ITO film, which the reverse time was adjusted
6
from 0 to 4.0 μs. The reverse time had no influence on the resistivity of ITO film. But the reverse time had the strong influence on crystal structure and growth model of ITO film. With the increase of reverse time, the value of high power sputtering part increased gradually, which resulted in the crystal structure of ITO film changing from no preferred orientation to (100) preferred orientation. Besides, the growth rate and carrier concentration increased gradually, too. Finally, for extending the application field of ITO film, it is interesting to prepare ITO film with (100) preferred orientation. The high sputtering power part of DC pulsed sputtering process could be effectively adjusted by the reverse time, which is an ideal choice for preparing ITO film with (100) preferred orientation. The present work provides the deep understanding of reverse time for DC pulsed sputtering process, as well as the physicochemical mechanism happened behind the sputtering process. Acknowledgments This work was supported by National Natural Science Foundation of China (Nos. 51472039/51772038/51575074/61504017), Project of Dalian Youth Star of Science and Technology (No. 2015R071), Natural Science Foundation of Liaoning Province, China (Nos. 2015020182/191/653, 201602120), Project Sponsored by the Scientific Research Foundation for the Doctor, Liaoning Province, China (No. 201601248)，and Liaoning Province Key Laboratory of Metallurgical Equipment and Process Control, University of Science and Technology Liaoning. References [1] C. G. Granqvist, Solar Energy Mater. Sol. Cells 91 (2007) 1529-1598. [2] M. G. Helander, Z. B. Wang, J. Qiu, M. T. Greiner, D. P. Puzzo, Z. W. Liu, et. al., Science 332 (2011) 944-947. [3] K. Ellmer, Nat. Photonics 6 (2012) 809-817.
7
[4] J. Shi, L. Shen, F. Meng, Z. Liu, Materials Letters, 182 (2016) 32-35. [5] Q. Liu, G. Dong, Y. Xiao, F. Gao, M. Wang, Q. Wang, et. al., Materials Letters, 142 (2015) 232-234. [6] G. S. Zhu, H. R. Xu, J. J. Li, P. Wang, X. Y. Zhang, Y. D. Chen, et. al., Materials Letters, 194 (2017) 90-93. [7] H. Wang, H. Liu, W. Ding, W. Chai, Thin Solid Films 542 (2013) 415-419. [8] O. Stenzel, The physics of thin film optical spectra: an introduction, Springer-Verlag, Berlin, 2005. [9] K. W. Böer, Handbook of the physics of thin-film solar cells, Springer Berlin Heidelberg, New York, 2013. [10] Hualin Wang, Ph.D thesis, Preparation of high-quality indium tin oxide film used for organic light-emitting display, Dalian Jiaotong University, 2014 (in Chinese) [11] PCPDFWIN card number: 00-06-0416 (Version 2.1, Copyright 2000) [12] T. Sasabayashi, N. Ito, E. Nishimura, M. Kona, P. K. Song, K. Utsumi, et. al., Thin Solid Films 445 (2003) 219-223. [13] D. A. Kirienko and O. Y. Berezina, Semiconductors 51 (2017) 823-827. [14] M. A. Lieberman and A. J. Lichtenberg, Principles of plasma discharges and materials processing, Second Edition, Wiley-Interscience, Hoboken, 2005. [15] T. Ma, X. Hu, Y. Chen, The principles of plasma physics, Revised Edition, University of Science and Technology of China Press, 2012 (in Chinese). [16] Z. Lv, J. Liu, D. Wang, H. Tao, W. Chen, H. Sun, et. al., A simple route to prepare (100) preferred orientation indium tin oxide film onto polyimide substrate by direct current pulsed magnetron sputtering, Materials Chemistry and Physics, Accepted.
8
Fig. 1. XRD patterns of ITO films deposited with different reverse time.
9
Fig. 2. The growth rate, band gap, concentration, and mobility of ITO film deposited with different reverse time.
10
Fig. 3. DC pulse voltage waveform with different reverse time (a). The diagram of dividing DC pulse voltage waveform (b).
11
Fig. 4. The calculated and measured power with different reverse time (a), which Pr, Pa, T, and R was the average power in Region 2 and 3, average power in one period, period, and reverse time, respectively. The equivalent power arrangement for different reverse time (b).
12
Increasing reverse time to 4.0 μs, ITO film change to (100) texture gradually.
ITO film with (100) texture displays better carrier concentration and band gap.
High sputtering power region improve kinetic energy of incident In/Sn/O ion/atom.
Incident In/Sn/O with higher kinetic energy result in ITO film with (100) texture.
13
S0167-577X(18)30343-4 https://doi.org/10.1016/j.matlet.2018.02.129 MLBLUE 23955
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
11 December 2017 27 January 2018 27 February 2018
Please cite this article as: W. Chen, H. Sun, H. Wang, W. Jiang, S. Liu, C. Liu, N. Wang, Y. Cui, W. Chai, W. Ding, B. Han, A deep understanding of relationship between reverse time and growth of ITO film deposited by direct current pulsed sputtering, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.02.129
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A deep understanding of relationship between reverse time and growth of ITO film deposited by direct current pulsed sputtering Weichao Chena, Haoting Suna, Hualin Wanga, Weiwei Jianga, Shimin Liua, Chaoqian Liua, Nan Wanga, Yunxian Cuia, Weiping Chaia, Wanyu Dinga,1, Bing Hanb,2 a
b
Dalian Jiaotong University, Dalian 116028, China.
Liaoning Province Key Laboratory of Metallurgical Equipment and Process Control, University of Science and Technology Liaoning, Anshan 114051, China.
Abstract: Indium tin oxide (ITO) film was deposited by the traditional direct current (DC) pulsed magnetron sputtering technology. With the increase of reverse time from 0 to 4.0 μs, the crystal structure of ITO film changed from the polycrystalline structure without preferred orientation to (100) preferred orientation. ITO film with (100) preferred orientation showed the satisfactory optical and electrical properties, such as the band gap in 4.15 eV and carrier concentration in 4.25×1020/cm3. Based on DC pulsed voltage waveform, the formation of (100) preferred orientation, as well as the change of optical and electrical properties of ITO film, were analyzed logically. Keywords: Indium tin oxide; Thin films; Sputtering; Reverse time; Preferred orientation; Optical and electrical property 1. Introduction Indium tin oxide (ITO) film has been widely employed in the photo-electric and electro-optical conversion fields, which was mainly used as the transparent conductive electrode [1-3]. In the industry fields, ITO film was mainly prepared by 1
2
Co-Corresponding author: Dr./Prof. Wanyu Ding E-mail: [email protected] and [email protected] Address: College of Materials Science and Engineering, Dalian Jiaotong University, No. 794 Huanghe Road, Shahekou District, Dalian, Liaoning Province/116028, China. Co-Corresponding author: Dr./Prof. Bing Han E-mail: [email protected] and [email protected] Address: College of Mechanical Engineering & Automation, University of Science and Technology Liaoning, No. 185 Qianshanzhong Road, Qianshan District, Anshan, Liaoning Province/114051, China.
1
the sputtering technology, such as direct current (DC), radio frequency, medium frequency, and so on [4-6]. Now, ITO film could also be prepared by DC pulsed sputtering, which had the advantage of high sputtering efficiency [7]. The growth model of ITO film was strongly influenced by DC pulsed sputtering parameters, such as power density, frequency, especially for reverse time. In turn, the crystal structure and optical-electrical properties of ITO film could be strongly influenced by the reverse time. But, the sputtering mechanism behind different reverse time was still not deeply understood. In our experiment, ITO films were deposited by DC pulsed magnetron sputtering technology. The aim is to deeply understand the relationship between reverse time, preferred orientation, and optical-electrical properties of ITO film, as well as the physicochemical mechanism behind them. 2. Experimental ITO film was deposited onto the quartz substrate, which was sputtered from ITO target by pure Ar gas. The sputtering power was supplied by Pinnacle™ Plus+ 5 kW DC pulsed power supply unit. DC pulsed sputtering power and pulse frequency was kept at 600 W and 100 kHz, respectively. The reverse time was adjusted from 0 to 4.0 μs. The crystal structure, electrical, and optical property of ITO film was analyzed by PANalytical Empyrean X-ray diffraction (XRD) system, Hall 8800 system, and U-3310 UV spectrophotometer, respectively. Based on Tauc relationship, the band gap of ITO film could be deduced [8, 9]. Because the sputtering process was carried out by pure Ar gas, the composition and chemical bond structure of ITO film was same for all reverse time [10]. The thickness of ITO film was kept at 301.4±5.5 nm for all reverse time. In turn, the growth rate of ITO film could be deduced. During the sputtering process, the sputtering voltage waveform of pulsed power supply unit was recorded by Tektronix TDS 2022B oscilloscope. The detailed deposition parameters
2
and measurement information could be found in Supplementary. 3. Results and discussion The crystal structure of ITO film was shown in Fig. 1. From Fig. 1, it can be seen clearly that all XRD patterns displayed the diffraction peaks attributed to cubic ferrite In2O3 (222) and (400) phase, respectively [11-13]. It can be found that all diffraction peaks shifted toward the small angle, which was explained in Supplementary. While, the most important feature of Fig. 1 was that with the increase of reverse time from 0 to 4.0 μs, the relative intensity of (222) and (400) peak gradually became weaker and stronger, respectively. Especially for ITO film with reverse time in 4.0 μs, (400) peak became the main one, which meant ITO film with (100) preferred orientation.
Fig. 1. XRD patterns of ITO films deposited with different reverse time. Hall measurement results showed that the resistivity was kept at 6.16±0.29×10-4 Ω·cm for all ITO films. In general, because of almost constant resistivity, perhaps the conclusion was drawn that the reverse time had no influence on the properties of ITO film. In order to deeply understand the relationship between reverse time and properties of ITO film, the relevant measurement results were shown in Fig. 2. From Fig. 2, it can be seen that with the increase of reverse time from 0 to 4.0 μs, the growth rate, band gap, and carrier concentration increased from 1.12 to 1.85 nm/s, 3.92 to 4.15 eV, and 2.93 to 4.25×1020/cm3, respectively. On the contrary, the carrier mobility decreased from 31.58 to 23.89 cm2/Vs. Combining the results in Fig. 1 and 2, it can be found that the reverse time had a strong influence on the crystal structure, growth rate, optical, and electrical properties of ITO film.
3
Fig. 2. The growth rate, band gap, concentration, and mobility of ITO film deposited with different reverse time. In order to deeply understand the sputtering process, DC pulsed voltage waveform was recorded, just as shown in Fig. 3 (a). One pulsed period could be divided into Region 1, 2, and 3, which was the reverse time, high power time, and low power time respectively, just as shown in Fig. 3 (b). The calculation result showed that the sum work in Region 1, 2, and 3 was almost same for all reverse time. Besides, the work in Region 1 could be negligible for all reverse time. So only sum work in Region 2 and 3 was considered, which really contributed to the sputtering process. Then, the average power in Region 2 and 3 could be theoretically calculated and actually measured, which corresponded well each other, just as shown in Fig. 4 (a). Based on the result in Fig. 4 (a), the equivalent power arrangement for different reverse time was shown in Fig. 4 (b). The details of measured and calculated work/power could be found in Supplementary. From Fig. 4 (b), it can be found that with the increase of reverse time, the average power in Region 2 increased gradually, except a little decrease for reverse time of 4.0 μs.
Fig. 3. DC pulse voltage waveform with different reverse time (a). The diagram of dividing DC pulse voltage waveform (b).
4
Fig. 4. The calculated and measured power with different reverse time (a), which Pr, Pa, T, and R was the average power in Region 2 and 3, average power in one period, period, and reverse time, respectively. The equivalent power arrangement for different reverse time (b). Based on the analysis of DC pulse sputtering process in Fig. 3 and 4, the change in Fig. 1 and 2 could be logically discussed. Firstly, in case of DC sputtering process, the sputtering power was fixed at lower value, which resulted in the incident In, Sn, and O atom/ion without kinetic energy higher enough and all kinetic energy was lost as the heat through inelastic collision. Besides, based on the plasma theory [14, 15], the mean free path of 0.6 Pa was about 100-101 cm, which was similar to the distance between target and substrate. So it was hard for In, Sn, and O atom/ion in plasma to collide each other. So In, Sn, and O atom/ion in plasma was incident onto the growth surface of ITO film, directly. Combining above reasons, the incident In, Sn, and O atom/ion was located at ITO film growth surface randomly, which resulted in the random chemical bond and random crystal growth direction. So in case of DC sputtering process, XRD pattern displayed no preferred orientation. Secondly, with the increase of reverse time, the sputtering process began with the high power, and ended with the low power. In high power sputtering process, In, Sn, and O atom/ion contented the higher kinetic energy. In this situation, these particles arrived at ITO film growth surface with kinetic energy higher enough, which couldn’t be totally lost as the heat through inelastic collision. So part of kinetic energy was transformed as the crystal energy in ITO crystal lattices, which could result in the growth of ITO grains along the certain direction. Besides, based on the film growth
5
ratio, the sputtering yield in high power part was much higher than that in low power part, which in turn decreased the mean free path at high power part. So one reasonable hypothesis should be considered, which was the reactive collision between In, Sn, and O atom/ion in plasma. Except the elastic/inelastic collision between In, Sn, and O atom/ion in plasma, the reactive collision between them could chemically product In-O/Sn-O groups, which was the key point in our experiment. For the growth surface of ITO film, the incident In-O/Sn-O groups also arranged themselves at the positions with lowest energy, which resulted in the formation of columnar grain along the normal direction of ITO film surface [16]. The detailed results and discussion about formation of columnar grain were shown in Supplementary. Combining above reasons, with the increase of reverse time, the value of high power increased, which resulted in more columnar grains appeared in ITO film. In turn, with the increase of reverse time, ITO film displayed more obvious (100) preferred orientation, just as shown in Fig. 1. Above analysis indicated that the high power sputtering process influenced ITO grain growth models, obviously. Based on the different ITO grain growth models, the change of optical and electrical properties of ITO film in Fig. 2 could be deeply understood. With the increase of reverse time, ITO grain growth mode changed from the equiaxed grain to columnar grain, which could improve the band gap and carrier concentration. On the contrary, the grain boundary between columnar had a little influence to the carrier mobility. The detailed discussion could be found in Supplementary. 4. Conclusions In summary, the traditional direct current pulsed magnetron sputtering technology was employed to prepare ITO film, which the reverse time was adjusted
6
from 0 to 4.0 μs. The reverse time had no influence on the resistivity of ITO film. But the reverse time had the strong influence on crystal structure and growth model of ITO film. With the increase of reverse time, the value of high power sputtering part increased gradually, which resulted in the crystal structure of ITO film changing from no preferred orientation to (100) preferred orientation. Besides, the growth rate and carrier concentration increased gradually, too. Finally, for extending the application field of ITO film, it is interesting to prepare ITO film with (100) preferred orientation. The high sputtering power part of DC pulsed sputtering process could be effectively adjusted by the reverse time, which is an ideal choice for preparing ITO film with (100) preferred orientation. The present work provides the deep understanding of reverse time for DC pulsed sputtering process, as well as the physicochemical mechanism happened behind the sputtering process. Acknowledgments This work was supported by National Natural Science Foundation of China (Nos. 51472039/51772038/51575074/61504017), Project of Dalian Youth Star of Science and Technology (No. 2015R071), Natural Science Foundation of Liaoning Province, China (Nos. 2015020182/191/653, 201602120), Project Sponsored by the Scientific Research Foundation for the Doctor, Liaoning Province, China (No. 201601248)，and Liaoning Province Key Laboratory of Metallurgical Equipment and Process Control, University of Science and Technology Liaoning. References [1] C. G. Granqvist, Solar Energy Mater. Sol. Cells 91 (2007) 1529-1598. [2] M. G. Helander, Z. B. Wang, J. Qiu, M. T. Greiner, D. P. Puzzo, Z. W. Liu, et. al., Science 332 (2011) 944-947. [3] K. Ellmer, Nat. Photonics 6 (2012) 809-817.
7
[4] J. Shi, L. Shen, F. Meng, Z. Liu, Materials Letters, 182 (2016) 32-35. [5] Q. Liu, G. Dong, Y. Xiao, F. Gao, M. Wang, Q. Wang, et. al., Materials Letters, 142 (2015) 232-234. [6] G. S. Zhu, H. R. Xu, J. J. Li, P. Wang, X. Y. Zhang, Y. D. Chen, et. al., Materials Letters, 194 (2017) 90-93. [7] H. Wang, H. Liu, W. Ding, W. Chai, Thin Solid Films 542 (2013) 415-419. [8] O. Stenzel, The physics of thin film optical spectra: an introduction, Springer-Verlag, Berlin, 2005. [9] K. W. Böer, Handbook of the physics of thin-film solar cells, Springer Berlin Heidelberg, New York, 2013. [10] Hualin Wang, Ph.D thesis, Preparation of high-quality indium tin oxide film used for organic light-emitting display, Dalian Jiaotong University, 2014 (in Chinese) [11] PCPDFWIN card number: 00-06-0416 (Version 2.1, Copyright 2000) [12] T. Sasabayashi, N. Ito, E. Nishimura, M. Kona, P. K. Song, K. Utsumi, et. al., Thin Solid Films 445 (2003) 219-223. [13] D. A. Kirienko and O. Y. Berezina, Semiconductors 51 (2017) 823-827. [14] M. A. Lieberman and A. J. Lichtenberg, Principles of plasma discharges and materials processing, Second Edition, Wiley-Interscience, Hoboken, 2005. [15] T. Ma, X. Hu, Y. Chen, The principles of plasma physics, Revised Edition, University of Science and Technology of China Press, 2012 (in Chinese). [16] Z. Lv, J. Liu, D. Wang, H. Tao, W. Chen, H. Sun, et. al., A simple route to prepare (100) preferred orientation indium tin oxide film onto polyimide substrate by direct current pulsed magnetron sputtering, Materials Chemistry and Physics, Accepted.
8
Fig. 1. XRD patterns of ITO films deposited with different reverse time.
9
Fig. 2. The growth rate, band gap, concentration, and mobility of ITO film deposited with different reverse time.
10
Fig. 3. DC pulse voltage waveform with different reverse time (a). The diagram of dividing DC pulse voltage waveform (b).
11
Fig. 4. The calculated and measured power with different reverse time (a), which Pr, Pa, T, and R was the average power in Region 2 and 3, average power in one period, period, and reverse time, respectively. The equivalent power arrangement for different reverse time (b).
12
Increasing reverse time to 4.0 μs, ITO film change to (100) texture gradually.
ITO film with (100) texture displays better carrier concentration and band gap.
High sputtering power region improve kinetic energy of incident In/Sn/O ion/atom.
Incident In/Sn/O with higher kinetic energy result in ITO film with (100) texture.
13