Journal of Crystal Growth 310 (2008) 284–289 Controlling of preferential growth mode of ZnO thin films grown by atomic layer deposition A. Wo´jcik à , M. Godlewski 1 , E. Guziewicz, R. Minikayev, W. Paszkowicz Institute of Physics, Polish Academy of Sciences, Al. Lotniko´w 32/46, 02-668 Warsaw, Poland Received 23 July 2007; received in revised form 1 October 2007; accepted 5 October 2007 Communicated by K.W. Benz Available online 10 October 2007 Abstract A method of controlling a preferred orientation of ZnO thin films grown by Atomic Layer Deposition (ALD) is discussed. The results for ALD films grown at low temperature with zinc acetate as a zinc precursor are presented. We demonstrate that to control a preferential growth mode one has to correlate growth temperature and separation time (so-called purging time) between pulses of precursors. r 2007 Elsevier B.V. All rights reserved. PACS: 68.55.Jk; 68.55.Nq; 78.66.Hf; 81.15.Kk Keywords: A1. Crystal structure; A1. Low temperature growth; A3. Atomic layer deposition; B1. Zinc acetate; B2. Zinc oxide 1. Introduction Wide band gap wurtzite phase ZnO has attracted attention due to its versatility in many promising applica- tions. For example, thin polycrystalline ZnO films are suitable materials for piezoelectric transducers, phosphors, chemical and gas sensors, surface acoustic wave (SAW) devices, and also for transparent conducting films in photovoltaic devices [1,2]. Such thin films of ZnO can be prepared by several growth techniques: by sol–gel method [3–6], sputtering [7–10], by various versions of pulsed laser deposition (PLD) [11–14], metal organic chemical vapor deposition (MOCVD) [15–17], and atomic layer deposition (ALD) [18–21]. Quality of ZnO films obtained by these methods depends on a growth method and on growth conditions. In particular, as we demonstrate in the present work, preferential orientation of ZnO films depends on growth conditions. This may be a problem since it is often essential to control orientation of films for a given application. For example, for devices which make use of piezoelectric properties of ZnO, and for SAW devices the preferred orientation (PO) is the one with c-axis perpendi- cular to the substrate [22]. In turn, ZnO films with (1 0 .0) orientation, are suitable for transparent conductive oxide (TCO) applications [18]. Anyway, the most densely packed and thermodynamically favorable growth orientation in wurtzite structure is the one with the c-axis perpendicular to a substrate. ZnO films with c-axis normal to the substrate are thus preferred in most of the cases. In this paper we show how to control PO of polycrystal- line ZnO thin film grown by ALD using zinc acetate as zinc precursor. Among numerous papers about thin films of ZnO by ALD, there are only very few about zinc acetate (Zn(OAc) 2 ) as the zinc precursor [23–25]. Films obtained in early investigations by other groups were almost amor- phous [23]. Our films are polycrystalline with their PO dependent on growth parameters. The ALD technique employs surface reactions between precursors. Zinc acetate is very volatile zinc precursor, which enables to significantly reduce growth temperature in the ALD process. We have demonstrated recently that this enables to obtain ZnMnO films free of foreign phases [26] ARTICLE IN PRESS www.elsevier.com/locate/jcrysgro 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2007.10.010 à Corresponding author. Tel.: +48 22 843 66 01x3507; fax: +48 22 847 52 23. E-mail address: awojcik@ifpan.edu.pl (A. Wo´jcik). 1 Also at: Department of Mathematics and Natural Sciences College of Science, Cardinal S. Wyszyn´ski University, Warsaw, Poland.