摘要
本文采用直流磁控溅射技术在玻璃衬底上制备ZnO:Al透明导电薄膜,研究了衬底温度、溅射功率、退火气氛等工艺参数对薄膜性能的影响,并对薄膜其影响机制进行了探讨。在此基础上,以实现高质量ZnO:Al薄膜的低温沉积为目标,采用在溅射气氛中引入H2和ZnO:Al靶、Zn靶两靶共溅射两种方法制备ZnO:Al薄膜来改善低温沉积下的电学性质。得出以下主要结果:
(1)采用直流(DC)磁控溅射技术,以ZnO:Al陶瓷靶(ZnOwt%:Al2O3wt%=98:2)为靶材,在玻璃衬底上制备高透明和高导电的ZnO:Al薄膜。所制备的ZnO:Al薄膜均为具有(002)面择优取向的六角纤锌矿结构且c轴垂直于衬底,薄膜的晶粒尺寸均在18-32nm之间。
(2)衬底温度、溅射功率和退火气氛等因素对薄膜的结构、光学及电学性能均有很大的影响。衬底温度为400℃、溅射功率为120 W时,ZnO:Al薄膜的结晶性能最好。所有的ZnO:Al薄膜在可见光区域均表现出了良好的透过性能。随着衬底温度的升高,薄膜电阻率下降,当衬底温度为500℃时,ZnO:Al薄膜的电阻率降到最低,在真空、Ar气等气氛下退火后,ZnO:Al薄膜电阻率降低,而在O2,N2和空气等气氛下退火后,ZnO:Al薄膜电阻率增加。
(3)采用在溅射气氛中通入H2、衬底温度为200℃的低温条件下制备ZnO:Al薄膜。随着溅射气氛中H2流量的增加,薄膜的晶粒尺寸减小,载流子浓度上升,电阻率下降;薄膜在400-900 nm范围内透过率均保持的90%以上,体现出良好的光透性能。
(4)首次采用ZnO:Al靶和Zn靶两靶共溅射的方法,研究了Zn靶功率和衬底温度对薄膜性能的影响。随着Zn靶的溅射功率的增加,ZnO:Al薄膜的晶面间距增大,载流子浓度升高,而电阻率随之下降,这主要由于Zn填隙浓度增加造成。还发现在两靶共溅射模式下,随着衬底温度的升高,ZnO:Al薄膜的结构性能、光透过性能学和电导性能均有所改善。
In this paper ZnO:Al transparent conductive fims were deposited on glass substrate by using DC magnetron sputtering technique. The effects of substrate temperature, sputtering power and annealing atmosphere on the film structure, optical and electrical properties have been studied systemically, and the mechanisms of electrical property are discussed. In addition, in order to realize high quanity ZnO:Al films deposition at low temperature, H-doping and ZnO:Al target, Zn target co-sputtering methods are applied to grow ZnO:Al films, the influence of H2 flows, the power on Zn target and substrate temperature on ZnO:Al films properties were investigated in details separately. The main results obtained as follows:
(1) ZnO:Al thin films have been deposited on glass substrate applying ZnO:Al ceramic target by DC magnetron sputtering. All the ZnO:Al films with the preferential orientation of (002) plane are polycrystalline and possess hexagonal wurtzite structure with their crystallographic c-axis perpendicular to the substrate. The grain size of the films is between 18-32 nm.
(2) Substrate temperature, sputtering power and annealing atmosphere have great influences on structure, optical and electrical properties of ZnO:Al films. The crystalline quality of ZnO:Al film is best when the film was prepared under 120 W of sputtering power and 400℃of substrate temperature. All the films show good transmittance during the visible region. Resistivity decrease with the increasing of substrate temperature; the resistivity drops to the lowest, when the film was prepared at 500℃; after annealing in vacuum and Ar, the resistivity drop, but after annealing in O2, N2 and air, the resistivity rise.
(3) To realize high quanity ZnO:Al films deposition at low temperature, The effects of H2 flows in the sputtering atmosphere on the properties of ZnO:Al films are studied. As the H2 flow incresing, grain size decreases, carrier concentration increases and resistivity drops. The transmittance of ZnO:Al films is above 90% from 400-900 nm, indicating excellent optical property.
(4) The influence of power on Zn target and substrate temperature on the properties of ZnO:Al films is studied by using ZnO:Al target, Zn target co-sputtering. With the increasing of the power on Zn target, the content of Zn element rise and the crystalline distance increases, which may be result of the the increasement of the concentration of Zn interstitial, carrier concentration goes up and resistivity drops correspondingly. With the increasing of substrate temperature, the structure, transmittance and resistivity have been improved.
引文
[1]R. Oesterlein, H. Krokoszinski, Optical dispertion in electron-beam-evaporated indium tin oxide thin films.1989,175:241
[2]J. E. Jaffe, A. C. Hess. Hartree-Fock study of phase changes in ZnO at high pressure. Phy. Rev. B,1993,48:7903
[3]孙柏.PLD技术制备ZnO薄膜及其结构和发光性质的研究.[博士学位论文].合肥:中国科学技术大学,2007
[4]黄昆,谢希德.半导体物理学.北京:科学出版社,1958.236
[5]E.L. Papadopoulou, M. Varda, K. Kouroupis-Agalou, M. Androulidaki, E. Chikoidze, P. Galtier, G. Huyberechits, E. Aperathitis. Undoped and Al-ZnO films with tuned properties grown by pulsed laser deposition. Thin solid films,2008, (516): 8141
[6]Klaus Ellmer, Rainald Mientus. Carrier transport in polycrystalline ITO and ZnO:Al Ⅱ:the influence of grain barriors and boundaries. Thin Solid Films,2008, 516:4620
[7]M.Chen, Z.L.Pei, X.Wang, et al. Structural, electrical, and optical properties of transparent conductive oxide ZnO:Al films prepared by magnetron reactive sputtering. J. Vac. Sci. Technol,2001, A19(3):963
[8]Wei Li, Yun sun, Yaxin Wang, et al. Effects of substrate temperature on the properties of facing-target sputtered Al-doped ZnO films. Sol. Energy Mater. Sol. Cells,2007,91(8):659
[9]F. Couzinie-Devy, N. Barreau, J. Kessler. Dependence of ZnO:Al properties on the substrate to target position in RF sputtering. Thin solid films,2008, (516):7049
[10]V. Khranovskyy, A. Ulyashin, G. Lashkarev, B.G. Svensson, R. Yakimova. Morphology, electrical and optical properties of undoped ZnO layers deposited on silicon substrates by PEMOCVD. Thin solid films,2008, (516):1396
[11]X.H. Wang, B. Yao, C.X. Cong, et al. Hole transport properties of P-type polycrystalline ZnO film using a dual-acceptor doping method with lithium and nitrogen. Thin solid films,2010 (518):3428
[12]M. Joseph, H. Tabata, H. Saeki, K. Ueda, Fabrication of the low-resistive p-type ZnO by codoping method. Physica B,2001, (302-303):140
[13]Martin A. Green, Keith Emery, Yoshihiro Hishikawa, Wilhelm Warta. Solar cell efficiency tables (Version 32). Prog. Photovolt:Res Appl,2008, (16):435
[14]刘彦松,王连卫等.用PLD法制备声表面滤波器件用ZnO薄膜.功能材料,2001,32(1):78-90
[15]S.Hayyamizu, H.Tabata, H.Tanaka, et al. Preparation of crystallized zinc oxide films on amorphous glass substrates by pulsed laser deposition. J Appl Phys,1996,80: 787
[16]H.Kim, C.M.Gilmore, et al. Transparent conducting aluminum-doped zinc oxide thin films for organic light-emitting devices. Appl Phys Lett,2000,76(3):259
[17]BaoHeng Sang, Seiichi Suzuki, Akira Yamada, et al. Growth of low resistive textured ZnO films by atomic layer deposition and their application to a-Si solar cells. 14th European photovoltaic solar conference, Barcelona, Spain,1997.613
[18]Y. Yamamoto, K. Saito, K. Takahashi, et al. Preparation of boron doped ZnO thin films by photoatomotic layer deposition. Sol. Energy Mater. Sol. Cells,2001,65:125
[19]Baosheng Sang, Nagoya Yoshinori, Kushiya Katsumi. MOCVD-ZnO windows for 30cm×30cm GIGS-based modules. Sol. Energy Mater. Sol. Cells,2003,75:179
[20]Xinlian Cheng, buheng Xu, Ying Zhao, et al. Boron-doped ZnO films for a-Si solar cell grown by MOCVD.15th International Photovoltaic Science and Engineering Conference, Shanghai, China,2005.557
[21]王兆阳,胡礼中,孙捷,等.激光分子束外延技术及其在氧化锌薄膜制备中的应用.中国稀土学报,2003,21(增刊):141
[22]梁红伟,吕有明,申德振,等.等离子体增强分子束外延生长ZnO薄膜及光电特性研究.人工晶体学报,2003,32(6):579
[23]姜海清,王连星,赵世民,等.溶胶-凝胶法制备Al3+离子掺杂型ZnO薄膜与评价.功能材料,2000,31(3):278
[24]Jin-Hong Lee, Byung-Ok Park. Transparent Conductive ZnO:Al, In and Sn thin films deposited by the sol-gel method. Thin solid films,2003,426:94
[25]W Tang, D C Cameron. Aluminum-doped zinc oxide transparent conductors deposited by the sol-gel process. Thin solid films,1994,238:83
[26]汪雷.ZnO薄膜生长技术的最新研究进展.材料导报,2002,16(9):33
[27]王华.特色功能材料-透明导电氧化物薄膜.材料导报,2005,19(11):101
[28]M N Islam, B K Samantaray, K L Chopra, et al. Microstructural characterization of transparet conducting aluminium doped zinc oxide films prepared by spray pyrolysis. Sol. Energy Mater. Sol. Cells,1993,29:27
[29]C. Trejo-Cruz, A. Mendoza-Galvan, A. M. Lopez-beltran et al. Effects of air annealing on the optical, electrical, and structural properties of indium-tin oxide thin films. Thin solid films,2009,517:4615
[31]J Mcller, O Kluth, S Wieder, et al. Development of highly efficient thin film silicon solar cells on textured-etched zinc oxide-coated glass substrates. Sol. Energy Mater. Sol. Cells,2001, (66):275
[32]T Repmann, W Appenzeller, T Roschek, et al. Large area deposition of intrinsic microcrystalline silicon for thin film solar cells. In:Proceedings of the 28th IEEE Photovoltaic Specialists Conference, Anchorage, Alaska,2000,912
[33]周继承,李莉.溅射气压对ZnO透明导电薄膜光电性能的影响.中国有色金属学报,2009,19(7):1278
[34]Jinsu Yoo, Jeonghul Lee, Seokki Kim, et al. High transmittance and low resistive ZnO:Al films for thin film solar cells. Thin solid films,2005, (480-481):213
[35]S A. V ingh., R. M Mefra., A Wakahara. et al. P-type conduction in codoped ZnO thin films. Journal of applied Physics,2003,93(1):396
[36]S. Ishizuka, K. Sakurai, A. Yamada, ea tl. Fabrication of wide-gap Cu(In1-xGax)Se2 thin film solar cells:a study on the correlation of cell performance with highly resistive i-ZnO layer thickness. Sol. Energy Mater. Sol. Cells.2005, (87): 541
[37]N Joel. Duenow, A Timothy. Gessert, David M. Wood, et al. Effects of hydrogen content in sputtering ambient on ZnO:Al electrical properties. Journal of Non-Crystalline Solids,2008,354:2787
[38]Jing-Chie Lin, Kun-Cheng Peng, C.A. Tseng, et al. Deposition of Al-doped and Al, Sc-co-doped zinc oxide by RF-and DC-sputtering of ZnO and Al-xSc (x=0,0.4 0.8 and 1.7 wt%) targets. Surface and Coating Technology,2008,202:5480
[39]Neelkanth G. Dhere. Presrnt status and future prospects of CIGSS thin film solar cells. Sol. Energy Mater. Sol. Cells,2006 (90):2181
[40]M. Suchea, S. Christoulakis, N. Katsarakis, et al. Comparative study of zinc oxide and aluminum doped zinc doped zinc oxide transparent thin films grown by direct current magnetron sputtering. Thin solid films,2007,515:6562
[41]W. W. Wang, X. G. Diao, Z. Wang, et al. Preparation and characterization of high-performance direct current magnetron sputtered ZnO:Al films. Thin solid films, 2005,491:54
[42]C. Platzer-Bjorkman, J Lu, J Kessler, L. Stolt. Interface study of CuInSe2/ZnO and Cu(In,Ga)Se2/Zn devices using ALD ZnO buffer layer. Thin solid films,2003, 431-432:321
[43]Alan E. Delahoy, Liangfan Chen, Masud Akhtar, et al. New technology for CIGS Photovoltaics. Solar Energy,2004,77:785
[44]W J Jeong, S K Kim, G C Park. Preparation and characteristic of ZnO thin film with high and low resistivity for an application of solar cell. Thin solid films,2006, 506-507:180
[45]张化福,袁玉珍,刘云燕.柔性透明导电膜ZAO.液晶与显示,2008,23(4):489
[46]Y. N. Xu, W. Y Ching. Electronic, optical, and structural properties of some wurtzite crystals. Phys. Rev. B.,1993,48 (7):4335
[47]Doron Azulay, Oded Millo, Isaac Balberg, et al. Current routes in polycrystalline CuInSe2 and Cu(In,Ga)Se2 films. Sol. Energy Mater. Sol. Cells.,2007(91):85
[48]Cetin Kilic, Alex Zungerb. N-type doping of oxides by hydrogen, Appl. Phys. Lett.,2002,81(1):73
[49]G Chris, Van de Walle. Hydrogen as a Cause of Doping in Zinc Oxide. Phys. Rev. Lett.,2000,85(5):1012
[50]S.F.J.Cox, E. A. Davis, S. P. Cottrell. Experimental Confirmation of the Predicted Shallow Donor Hydrogen State in Zinc Oxide. Phys. Rev. Lett.,2001,86(12):2601
[51]W. F. Liu, G. T. Du, Y. F. Sun, et al. Effects of hydrogen flux on the properties of Al-doped ZnO films sputtered in Ar+H2 ambient at low temperature. Applied Surface Science,2007,253:2999
[52]Liang-Yih Chen, Wen-Hwa Chen, Jia-Jun Wang and Franklin Chau-Nan Hong. Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering. Applied physicis letters,2004,85(23):5630
[53]Yanfeng Sun, Weifeng Liu, Zhidan He, et al. Novel properties of AZO film sputtered in Ar+H2 ambient at high temperature. Vacuum,2006,80:981
[54]郑伟涛等.薄膜生长及薄膜技术.北京:化学工业出版社,2004:68
[55]马全宝.透明的高导电近红外反射ZnO:Ga薄膜的制备及特性研究:[博士学位论文].杭州:浙江大学,2007
[56]许振嘉.半导体的检测与分析.北京:科学出版社,2006:473
[57]J N Zeng, J K Low and Z M Ren, et al. Effects of deposition conditions on the optical and electrical properties of ZnO films prepared by pulsed laser deposition. Appl. Surf. Sci.,2002 197-198:362
[58]Klaus Ellmer, Rainald Mientus. Carrier transport in polycrystalline transparent conductive oxides:A comparative study of zinc oxide and indium oxide. Thin Solid Films,2008,516:4620
[59]Xue-Yong Li, Hong-Jian Li, Zhi-Jun Wang et al. Effect of substrate temperature on the structural and optical properties of ZnO and Al-doped ZnO thin films prepared by dc magnetron sputtering. Opt. Commun.,2009247:247
[60]Qing Hua Li, Deliang Zhu, Wenjun Liu, et al. Optical properties of Al-doped ZnO thin films by ellipsometry. Appl. Surf. Sci.,2008,204:2922
[61]李小换,朱满康,侯育冬等.衬底温度对ZnO薄膜氧缺陷的影响.压电与声光,2004,4:318
[62]En-Gang Fu, Da-Ming Zhuang, Gong Zhang et al. Substrate temperature dependence of the properties of ZAO thin films deposited by magnetron sputtering. Appl. Surf. Sci.,2003,217:88
[63]孙柏,邹崇文,刘忠良等.衬底温度对PLD方法生长的ZnO薄膜结构和发光特性的影响.无机材料学报,2006,21:1005
[64]T Minami, Y Ohtani, T Miyata and T Kuboi. Transparent conducting Al-doped ZnO thin films prepared by magnetron sputtering with dc and rf power applied in combnation. Journal Vacuum Society Techology,2007, A25(4):1172
[65]N D Joel, A G, Timothy M W David, M B Teresa, et al. Transparent conducting zinc oxide thin films doped with aluminum and molybdenum. Journal Vacuum Society Techology,2007, A25(4):955
[66]H W Lee, S P Lau, Y G Wang. Structural, electrical and optical properties of Al-doped ZnO thin films prepared by filtered catholic vacuum are technique. Journal of Crystal Growth,2004,268(3/4):596
[67]G. Z. Xing, B. Yao, C. X. Cong, et al. Effect of annealing on conductivity behavior of undoped zinc oxide prepared by rf magnetron sputtering. Journal of Alloys and Compounds,2008,457:36
[68]C. Y. Zhang. The influence of substrate and annealing temperature on electrical properties of p-type ZnO films. Physica B,2009,404:138
[69]A. G. Rolo, J. Ayres de Campos, T. Viseu, et al. The annealing effect on structure and optical properties of ZnO thin films produced by r.f. sputtering. Superlattices and Microstructure 2007 42:265
[70]Sheng-Yuan Chu, Walter Water, Jih-Tsang Liaw, et al. Influnce of postposition annealing on the properties of ZnO films prepared by magnetron sputtering. Journal of the European Ceramic Society,2003,23:1593
[71]M. Bouderbala, S. Hamzaoui, M. Adnane, et al. Annealing effect on properties of transparent and conducting ZnO thin films. Thin Solid Films,2009,517:1572
[72]S K Sieber, N Wanderka, I Urban, et al. Electron microscopic characterization of reactively sputtered ZnO with differerent Al-doping levels. Thin solid films,1998, 330(2):108
[73]M. S. Jang, M. K. Ryu, M. Y. Yoon, et al. A study on the Raman spectra of Al-doped and Ga doped ZnO ceramics. Current Applied Physics,2009,9:651
[74]K Ellmer. Resistivity of polycrystalline zinc oxide films:current status and physical limit. J. Phys. D:Appl. Phys.,2001,34:3097
[75]Manoj Kumar, R. M. Mehra, Se-Young Choi. Effect of oxygen ambient on structural, optical and electrical properties of epitaxial Al-doped ZnO thin films on r-plane sapphire by pused laser deposition. Current Applied Physics,2009,9:737
[76]Dong-Joo Kwak, Min-Woo Park and Youl-Moon Sung et al. Discharge power dependence of structure and electrical properties of Al-doped ZnO conducting film by magnetron sputtering. Vaccum,2009,83:113