Transparent conducting films of zinc oxide and indium-doped zinc oxide have been prepared by a simple and economical sol-gel technique. This process is feasible for the fabrication of high quality TCO thin films when the processing parameters are optimized. It was found that the out-diffusion of oxygen during the vacuum annealing step was a crucial factor to prepare thin layer with superior properties. Annealing lowers the resistivity down to 4.7 10<sup>-3</sup> Ω · cm for the 1 at.% doped films due to the liberation of high-valency In-dopants and the enhanced film density. At high indium concentrations, the free electron density stabilizes because an increasing number of dopant atoms form some kinds of neutral defects. The neutralized indium atoms do not contribute free electrons. The feasibility to deposit highly transparent ZnO thin films has been demonstrated.
Jin, Z.-C., Hamberg, I. and Granqvist, C.G. (1988) Optical Properties of Sputter-Deposited ZnO:Al Thin Films. Journal of Applied Physics, 64, 5117. http://dx.doi.org/10.1063/1.342419
Lee, J.-H., Lee, S.-Y. and Park, B.-O. (2006) Fabrication and Characteristics of Transparent Conducting In2O3-ZnO Thin Films by Ultrasonic Spray Pyrolysis. Materials Science and Engineering B, 127, 267-271. http://dx.doi.org/10.1016/j.mseb.2005.10.008
Addou, M., Moumin, A., El Idrissi, B., Regragui, M., Bougrine, A., Kachouane, A. and Monty, C. (1999) Structural, Optical and Electrical Properties of Undoped and Indium Doped Zinc Oxide Prepared by Spray Pyrolysis. Journal de Chimie Physique, 96, 232-244. http://dx.doi.org/10.1051/jcp:1999133
Castaneda, L., Morales-Saavedra, O.G., Cheang-Wong, J.C., Acosta, D.R., Banuelos, J.G., Maldonado, A. and Olvera, M.L. (2006) Influence of Indium Concentration and Substrate Temperature on the Physical Characteristics of Chemically Sprayed ZnO:In Thin Films Deposited from Zinc Pentanedionate and Indium Sulfate. Journal of Physics: Condensed Matter, 18, 5105-5120. http://dx.doi.org/10.1088/0953-8984/18/22/010
Castaneda, L., Maldonado, A., Escobedo-Morales, A., Avendano-Alejo, M., Gómez, H. Vega-Pérez, J. and Olvera, M.L. (2011) Indium Doped Zinc Oxide Thin Films Deposited by Ultrasonic Spray Pyrolysis Technique: Effect of the Substrate Temperature on the Physical Properties. Materials Science in Semiconductor Processing, 14, 114-119. http://dx.doi.org/10.1016/j.mssp.2011.01.013
Biswal, R., Castaneda, L., Moctezuma, R., Vega-Pérez, J., Olvera, M.L. and Maldonado, A. (2012) Formation of Indium-Doped Zinc Oxide Thin Films Using Ultrasonic Spray Pyrolysis; the Importance of the Water Content in the Aerosol Solution and the Substrate Temperature for Enhancing Electrical Transport. Materials, 5, 432-442. http://dx.doi.org/10.3390/ma5030432
Major, S., Banerjee, A. and Chopra, K.L. (1984) Annealing Studies of Undoped and Indium-Doped Zinc Oxide. Thin Solid Films, 122, 31-43. http://dx.doi.org/10.1016/0040-6090(84)90376-6
Major, S., Banerjee, A. and Chopra, K.L. (1983) Highly Transparent and Conducting Indium-Doped Zinc Oxide Films by Spray Pyrolysis. Thin Solid Films, 108, 333-340. http://dx.doi.org/10.1016/0040-6090(83)90082-2
Reddy, P.S., Chetty, G.R., Uthanna, S., Naidu, S. and Reddy, P.J. (1991) Optical Properties of Spray Deposited ZnO Films. Solid State Communications, 77, 899-901. http://dx.doi.org/10.1016/0038-1098(91)90342-S
Ortiz, A. and Garcia, M. (1992) Photoluminescent Properties of Indium-Doped Zinc Oxide Films Prepared by Spray Pyrolysis. Thin Solid Films, 207, 175-180. http://dx.doi.org/10.1016/0040-6090(92)90119-V
Lo, C.Y., Hsu, C.L., Yu, Q.X., Lee, H.Y. and Lee, C.T. (2002) Investigation of Transparent and Conductive Undoped Zn 2 In 2 O 5-x Films Deposited on n-Type GaN Layers. Journal of Applied Physics, 92, 274. http://dx.doi.org/10.1063/1.1481207
Lim, J.H., Hwang, D.K., Kim, H.S., Oh, J.Y., Yang, J.H., Navamathavan, R. and Park, S.J. (2004) Low-Resistivity and Transparent Indium-Oxide-Doped ZnO Ohmic Contact to p-Type GaN. Applied Physics Letters, 85, 6191. http://dx.doi.org/10.1063/1.1826231
Nomura, K., Ohta, H., Ueda, K., Orita, M., Hirano, M. and Hosono, H. (2002) Novel Film Growth Technique of Single Crystalline In2O3(ZnO)m (m = integer) Homologous Compound. Thin Solid Films, 411, 147-151. http://dx.doi.org/10.1016/S0040-6090(02)00204-3
Galca, A.C., Socol, G. and Cracium, V. (2012) Optical Properties of Amorphous-Like Indium Zinc Oxide and Indium Gallium Zinc Oxide Thin Films. Thin Solid Films, 520, 4722-4725. http://dx.doi.org/10.1016/j.tsf.2011.10.194
Kim, P.Y., Lee, J.Y., Lee, H.Y., Lee, S.J. and Cho, N.I. (2008) Structure and Properties of IZO Transparent Conducting Thin Films Deposited by PLD Method. Journal of Korean Physical Society, 53, 207-211.
Jeon, J.W., Jeon, D.W., Sahoo, T., Kim, M., Baek, J.H., Hoffman, J.L., Kim, N.S. and Lee, I.H. (2011) Effect of Annealing Temperature on Optical Band-Gap of Amorphous Indium Zinc Oxide Film. Journal of Alloys and Compounds, 509, 10062-10065. http://dx.doi.org/10.1016/j.jallcom.2011.08.033
Ohashi, N., Ogino, T., Sakaguchi, I., Hishita, S., Komatsu, M., Takenaka, T. and Haneda, H. (2002) Fabrication of Epitaxial In2O3(ZnO)5 Thin Films by RF Sputtering and Their Characterization by X-Ray and Electron Diffraction Techniques. Journal of Crystal Growth, 237-239, 558-563. http://dx.doi.org/10.1016/S0022-0248(01)01980-7
Moriga, T., Okamoto, T., Hiruta, K., Fujiwara, A., Nakaayashi, I. and Tominaga, K. (2000) Structures and Physical Properties of Films Deposited by Simultaneous DC Sputtering of ZnO and In2O3 or ITO Targets. Journal of Solid State Chemistry, 155, 312-319. http://dx.doi.org/10.1006/jssc.2000.8919
Harding, G.L., Window, B. and Horrigan, E.C. (1991) Aluminum- and Indium-Doped Zinc Oxide Films Prepared by DC Magnetron Reactive Sputtering. Solar Energy Materials, 22, 69-91. http://dx.doi.org/10.1016/0165-1633(91)90007-8
Luna-Arredondo, E.J., Maldonado, A., Asomoza, R., Acosta, D.R., Meléndez-Lira, M.A. and de la L. Olvera, M. (2005) Indium-Doped ZnO Thin Films Deposited by the Sol-Gel Technique. Thin Solid Films, 490, 132.
Kim, M.S., Yim, K.G., Kim, S., Nam, G., Lee, D.Y., Kim, J.S., Kim, J.S. and Leem, J.Y. (2012) Growth and Characterization of Indium-Doped Zinc Oxide Thin Films Prepared by Sol-Gel Method. Acta Physica Polonica A, 121, 217- 220.
Bahadur, H., Srivastava, A.K., Sharma, R.K. and Chandra, S. (2007) Morphologies of Sol-Gel Derived Thin Films of ZnO Using Different Precursor Materials and Their Nanostructure. Nanoscale Research Letters, 2, 469-475. http://dx.doi.org/10.1007/s11671-007-9089-x
Bel Hadj Tahar, R., Ban, T., Ohya, Y. and Takahashi, Y. (1997) Optical, Structural, and Electrical Properties of Indium Oxide Thin Films Prepared by the Sol-Gel Method. Journal of Applied Physics, 82, 865-870. http://dx.doi.org/10.1063/1.365786
Major, S. and Chopra, K.L. (1988) Indium-Doped Zinc Oxide Films as Transparent Electrodes for Solar Cells. Solar Energy Materials, 17, 319-327. http://dx.doi.org/10.1016/0165-1633(88)90014-7
Bel Hadj Tahar, R. (2005) Structural and Electrical Properties of Aluminum-Doped Zinc Oxide Films Prepared by Sol-Gel Process. Journal of the European Ceramic Society, 25, 3301-3306. http://dx.doi.org/10.1016/j.jeurceramsoc.2004.08.028
Bel Hadj Tahar, R. and Bel Hadj Tahar, N. (2005) Crystallographic Orientation in Pure and Aluminum-Doped Zinc Oxide Thin Films Prepared by Sol-Gel Technique. Journal of the American Ceramic Society, 88, 1725-1728. http://dx.doi.org/10.1111/j.1551-2916.2005.00268.x
Lide, D.R. (1991) Handbook of Chemistry and Physics. 71st Edition, CRC Press, Boca Raton.
Bel Hadj Tahar, R. and Bel Hadj Tahar, N. (2005) Boron-Doped Zinc Oxide Thin Films Prepared by Sol-Gel Technique. Journal of Materials Science, 40, 5285-5289. http://dx.doi.org/10.1007/s10853-005-0522-1
Goyal, D.J., Agashe, C., Takwale, M.G., Bhide, V.G., Mahamuni, S. and Kulkarni, S.K. (1993) Dopant Induced Modifications in the Physical Properties of Sprayed ZnO:In Films. Journal of Materials Research, 8, 1052-1056. http://dx.doi.org/10.1557/JMR.1993.1052
Bel Hadj Tahar, R. and Bel Hadj Tahar, N. (2002) Mechanism of Carrier Transport in Aluminum-Doped Zinc Oxide. Journal of Applied Physics, 92, 4498-4501.
Jin, Z.C., Hamberg, I. and Granqvist, C.G. (1987) Optical Properties of Transparent and Heat Reflecting ZnO:Al Films Made by Reactive Sputtering. Applied Physics Letters, 51, 149-151. http://dx.doi.org/10.1063/1.99008
Frank, G. and Kostlin, H. (1982) Electrical Properties and Defect Model of Tin-Doped Indium Oxide Layers. Applied Physics A, 27, 197-206. http://dx.doi.org/10.1007/BF00619080
Ku, D.Y., Kim, I.H., Lee, I., Lee, K.S., Lee, T.S., Jeong, J.H., Cheong, B., Baik, Y.J. and Kim, W.M. (2006) Structural and Electrical Properties of Sputtered Indium-Zinc Oxide Thin Films. Thin Solid Films, 515, 1364-1369. http://dx.doi.org/10.1016/j.tsf.2006.03.040
Qiu, S.N., Qiu, C.X. and Shih, I. (1987) Air Heat Treatment of In-Doped ZnO Thin Films. Solar Energy Materials, 15, 261-267. http://dx.doi.org/10.1016/0165-1633(87)90041-4
Qiu, C.X. and Shih, I. (1986) Tin- and Indium-Doped Zinc Oxide Films Prepared by RF Magnetron Sputtering. Solar Energy Materials, 13, 75-84. http://dx.doi.org/10.1016/0165-1633(86)90036-5
Castro, M.S. and Aldao, C.M. (1999) Effects of the Sintering Temperature on the Oxygen Adsorption in ZnO Ceramics. Journal of the European Ceramic Society, 19, 511-515. http://dx.doi.org/10.1016/S0955-2219(98)00210-6
Srikant, V. and Clark, D.R. (1998) On the Optical Band Gap of Zinc Oxide. Journal of Applied Physics, 83, 5447. http://dx.doi.org/10.1063/1.367375
Pearton, S.J., Norton, D.P., Ip, K., Heo, Y.W. and Steiner, T. (2005) Recent Progress in Processing and Properties of ZnO. Progress in Materials Science, 50, 293-340.
Harvey, S.P., Poeppelmeier, K.R. and Mason, T.O. (2008) Subsolidus Phase Relationships in the ZnO-In2O3-SnO2 System. Journal of the American Ceramic Society, 91, 3683-3689. http://dx.doi.org/10.1111/j.1551-2916.2008.02686.x
Mari, B., Cembrero, J., Mollar, M. and Tortosa, M. (2008) Optical Properties of Zinc Oxide-Based Ternary Compounds Synthesized by Electrodeposition. Physica Status Solidi (c), 5, 555-558. http://dx.doi.org/10.1002/pssc.200776840
Sarkar, A., Ghosh, S., Chaudhuri, S. and Pal, A.K. (1991) Studies on Electron Transport Properties and the Burstein-Moss Shift in Indium-Doped ZnO Films. Thin Solid Films, 204, 255-264. http://dx.doi.org/10.1016/0040-6090(91)90067-8
Weijtens, C.H.L. and Van Loon, P.A.C. (1991) Influence of Annealing on the Optical Properties of Indium Tin Oxide. Thin Solid Films, 196, 1-10. http://dx.doi.org/10.1016/0040-6090(91)90169-X
Roth, A.P., Webb, J.B. and Williams, D.F. (1982) Band-Gap Narrowing in Heavily Defect-Doped ZnO. Physical Review B, 25, 7836-7839. http://dx.doi.org/10.1103/PhysRevB.25.7836
Caporaletti, O. (1982) Electrical and Optical Properties of Bias Sputtered ZnO Thin Films. Solar Energy Materials, 7, 65-73. http://dx.doi.org/10.1016/0165-1633(82)90097-1
Major, S., Banerjee, A. and Chopra, K.L. (1985) Optical and Electronic Properties of Zinc Oxide Films Prepared by Spray Pyrolysis. Thin Solid Films, 125, 179-185. http://dx.doi.org/10.1016/0040-6090(85)90411-0
Major, S., Banerjee, A. and Chopra, K.L. (1986) Electrical and Optical Transport in Undoped and Indium-Doped Zinc Oxide Films. Journal of Materials Research, 1, 300-310. http://dx.doi.org/10.1557/JMR.1986.0300
Burstein, E. (1954) Anomalous Optical Absorption Limit in InSb. Physical Review, 93, 632. http://dx.doi.org/10.1103/PhysRev.93.632
Sernelius, B.E., Berggren, K.F., Jin, Z.C., Hamberg, I. and Granqvist, C.G. (1988) Band-Gap Tailoring of ZnO by Means of Heavy Al Doping. Physical Review B, 37, 10244-10248. http://dx.doi.org/10.1103/PhysRevB.37.10244
Hamberg, I., Granqvist, C.G., Berggren, K.F., Sernelius, B.E. and Engstrom, L. (1984) Band-Gap Widening in Heavily Sn-Doped In2O3. Physical Review B, 30, 3240-3249. http://dx.doi.org/10.1103/PhysRevB.30.3240
Wolff, P.A. (1962) Theory of the Band Structure of Very Degenerate Semiconductors. Physical Review, 126, 405. http://dx.doi.org/10.1103/PhysRev.126.405
Dietz, R.E., Hopfield, J.J. and Thomas, D.G. (1961) Excitons and the Absorption Edge of ZnO. Journal of Applied Physics, 32, 2282. http://dx.doi.org/10.1063/1.1777060
Shooji, S., Minami, T., Takata, S. and Nanto, H. (1984) Rep. IECE of Japan Tech. Group on Electron Parts and Materials, CMP 84-4, 55.
Sernelius, B.E. (1987) Self-Energy Shifts in Heavily Doped, Polar Semiconductors. Physical Review B, 36, 4878-4887. http://dx.doi.org/10.1103/PhysRevB.36.4878
Hamberg, I. and Granqvist, C.G. (1986) Evaporated Sn-Doped In2O3 Films: Basic Optical Properties and Applications to Energy-Efficient Windows. Journal of Applied Physics, 60, R123-R159. http://dx.doi.org/10.1063/1.337534