ELSEVIER Thin Solid Films 305 (1997) 201-209 The physical properties of Al-doped zinc oxide films prepared by RF magnetron sputtering Ki Cheol Park a, Dae Young Ma a, Kun Ho Kim b,, Department of Electronic Materials Engineering and Research Center for Aircraft Parts Technology, Gyeongsang National University, Chinju 660-701, South Korea b Department of Physics and the Research Institute of Natural Science, Gyeongsang National UniL,ersity, Chinju 660-701, South Korea Received 17 October 1996; accepted 10 April 1997 Abstract Al-doped zinc oxide (AZO) films are prepared by RF magnetron sputtering on glass and Si substrates with specifically designed ZnO targets containing different amounts of A1203 powder as a doping source. The physical properties of the AZO films are investigated in terms of the preparation conditions, such as A120 3 content in the target, RF power (PRF), substrate temperature (T~) and working pressure (Pw). The crystal structure of the AZO film is hexagonal wurtzite, and all the films show the typical crystallographic orientation, with the c-axis perpendicular to the substrate. The growth rate increases with increasing Pro,, but decreases with increasing T~ and Pw. Films 1500 ,~ thick with the lowest resistivity (p) of 4.7 × 10 .4 ~ cm and the transmittance over 90% at the visible region are prepared by using norminal 3 wt.% A1203 target at T s = 150°C, Pw = 2 mTorr an d Pay = 150 W. Optical transmittance measurements show that AZO films are degenerate semiconductors with direct bandgap. The optical energy bandgap for undoped ZnO film is ~ 3.3 eV and those for AZO films increase as the carrier concentration (n e) in the film increases. The blue shift in the AZO films is proportional to one third power of he. © 1997 Elsevier Science S.A. PACS: 72.80.Ey; 81.15.Cd; 68.55 Ke~words: Electrical properties and measurements; Optical properties; Structural properties; Zinc oxide 1. Introduction Transparent conductive films such as ITO (tn203:Sn), NESA (SnO2), and ZnO have been widely studied for their practical applications as transparent electrodes, window materials in display, solar cell, and various optoelectronic devices [1-4]. ZnO films are very attractive due to the ease in doping of Si [5], Ga [6,7], AI, and so on. Al-doped ZnO (AZO or ZnO:A1) transparent conductive film has high transmittance in the visible region, low p, and, especially, the optical bandgap can be controlled by the A1 doping level [3,4,8-13]. Generally, AZO films are fabricated by vacuum evaporation, chemical vapor deposition (CVD), and sputter deposition. Sputter deposition is the most widely used technique for preparing AZO films [9,12,14,15]. For pure ZnO film growth, Zn target is used in Ar and 0 2 mixed gas ambient, but for AZO film growth, two types of targets can be applicable according to ' Correspondingauthor. 0040-6090/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S0040-6090(97)00215-0 the A1 doping method. One is the co-sputtering of an A1 target and a pure ZnO target [14], the other is the conven- tional sputtering of a ZnO + A120 3 target [3,9,12]. Studies on AZO films prepared by sputter deposition have shown that the AZO films were strongly oriented perpendicular to the substrate surface (c-axis orientation) with polycrystalline hexagonal wurtzite structure [8,10,11,14], and have the properties as transparent elec- trodes comparable to ITO or FTO (Fluorine-doped tin oxide) with p as low as 10 .4 f), cm and the optical transmittance ~ 90% in the visible region. They cost tess of raw material, have good thermal stability, and are stable in the hydrogen plasma ambient [3,11,16]. Thus, many studies have been concentrated to replace ITO or FrO [4-6]. The structural, optical, and electrical properties of AZO films are influenced by deposition parameters such as the AI20 3 content in the target, substrate temperature (T~), ambient gas and pressure (Pw), and RF power (PRF)' Therefore, it is meaningful to study the effects of the