Journal of Crystal Growth 306 (2007) 47–51 Strain relaxation and critical thickness for epitaxial LaAlO 3 thin films grown on SrTiO 3 (0 0 1) substrates by molecular beam epitaxy C. Merckling a,b,Ã , M. El-Kazzi a , G. Delhaye a , V. Favre-Nicolin c,d , Y. Robach a , M. Gendry a , G. Grenet a , G. Saint-Girons a , G. Hollinger a a INL—UMR5270/CNRS—Ecole Centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully, France b STMicroelectronics, 850 rue Jean Monnet, 38926 Crolles, France c CEA/DRFMC/SP2 M, 17 rue des Martyrs, 38054 Grenoble, France d Universite´Joseph Fourier, BP 53, 38041, Grenoble Cedex 9, France Received 1 December 2006; received in revised form 27 February 2007; accepted 23 April 2007 Communicated by M.S. Goorsky Available online 27 April 2007 Abstract This study investigates the tensile-strained growth of LaAlO 3 on SrTiO 3 (0 0 1) substrates by molecular beam epitaxy (MBE). Reflection high energy electron diffraction (RHEED) analysis shows that for thicknesses smaller than 3.8 nm, LaAlO 3 films grow pseudomorphically. Plastic relaxation starts for films thicker than this critical thickness of 3.8 nm. The in- and out-of-plane lattice parameters of the strain-relaxed layers have been measured by ex situ X-ray diffraction (XRD) at grazing angles. The relaxation mechanism is discussed on the basis of these experiments. r 2007 Elsevier B.V. All rights reserved. PACS: 81.15.Hi; 77.55.+f; 61.14.Hg Keywords: A1. AFM; A1. RHEED; A1. XRD; A3. MBE; B1. LaAlO 3 ; B2. High-k dielectrics 1. Introduction Crystalline perovskite thin films have been the scope of intensive research because of their dielectric, ferroelectric and magnetic properties. Crystalline LaAlO 3 (LAO) and SrTiO 3 (STO) are currently the object of many studies due to their potential use as gate oxides integrated on silicon for microelectronic applications [1]. Epitaxial oxides are believed to have superior potential properties because they should allow obtaining abrupt interfaces if coherently grown on Si. On the other hand, such LAO layers grown on STO(0 0 1) substrates could also be used for the fabrication of twin-free LAO/STO pseudosubstrates. It is known that commercial bulk LAO(0 0 1) substrates present a high concentration of twins that make them inappropriate for a wide range of applications. Finally, LAO/STO multi layers could also be the base for further development of innovating devices [2]. Hence, there is a strong interest to define growth conditions for pseudomorphic, partially or fully relaxed layers. The growth conditions of LAO layers prepared on STO(0 0 1) using pulsed layer deposition have already been studied by Fuchs et al. [3], Ohtomo and Hwang [4] and more recently by Maurice et al. [5]. In this study we used molecular beam epitaxy (MBE) to grow epitaxial LAO films on STO(0 0 1). The strain relaxation of the LAO films is investigated by in situ reflection high energy electron diffraction (RHEED) and by ex situ grazing incidence X-ray diffraction (GIXRD). The critical thickness for plastic relaxation is determined, and the relaxation mechanism is discussed. The surface morphology is studied by atomic force microscopy (AFM) in contact mode under room conditions. 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.2007.04.048 Ã Corresponding author. INL—UMR5270/CNRS—Ecole Centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully, France. E-mail address: clement.merckling@ec-lyon.fr (C. Merckling).