Study of epitaxial SrTiO 3 (STO) thin films grown on Si(0 0 1)–2  1 substrates by molecular beam epitaxy M.N.K. Bhuiyan * , A. Matsuda, T. Yasumura, T. Tambo, C. Tatsuyama Department of Electrical and Electronic Engineering, Faculty of Engineering, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan Abstract Perovskite-type oxide SrTiO 3 (STO) thin films with thicknesses of 30, 100, 300 and 1000 A ˚ have been grown epitaxially on Si(0 0 1) substrates using co-evaporation of Sr and Ti in an O 2 atmosphere of 9:0  10 8 Torr at 500 8C by molecular beam epitaxy (MBE). SrO buffer layers of 100 A ˚ have been grown at 350 8C on Si substrates. The SrTiO 3 films have been studied using reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) and atomic force microscopy (AFM) as a function of the thickness of STO films. By heating the Si(0 0 1) substrates at 800 8C under Sr exposure for 2 min after the chemical cleaning and formation of protective SiO 2 layer, RHEED patterns of the atomically clean Si(0 0 1)–2  1 surface have been observed. RHEED pattern becomes unclear after the growth of 30 and 100 A ˚ -thick STO films. On the contrary, spotty and streaky patterns, and spotty patterns are observed clearly for 300 and 1000 A ˚ -thick films, respectively. The surface crystallinity improves for all the samples after annealing at 800 8C. The STO films with thicknesses of 30 and 1000 A ˚ consist of grains in the images of atomic force microscopy. The flatness and crystallinity of STO films with the thickness of 100–300 A ˚ are better than the other films. # 2003 Elsevier Science B.V. All rights reserved. Keywords: STO film; Epitaxy; MBE; RHEED; AFM; Si 1. Introduction There have been several reports on the epitaxial growth of high-temperature cuprate oxide-supercon- ductor (Bi 2 Sr 2 Ca n1 Cu n O x ) thin films on SrTiO 3 (0 0 1) substrates by molecular beam epitaxy (MBE) [1–3]. There has also been much interest in the application of superconductor films on Si substrates to electronic devices [4,5]. This process is complicated by the reac- tivity of the Si surfaces, which areoxidized easily, as well as the mismatch of lattice constants between Si and the grown films. For these reasons, buffer layers are needed for the growth of SrTiO 3 (STO) films. The epitaxial STO thin films also serve as an excellent buffer layer for subsequent heteroepitaxy of various functional oxides including ferroelectric [6] and high-T c superconductor [7] thin films on Si substrates. The dielectric constants at room temperature of STO and SrO are 300 and 3.2, respectively. So far, there have been a few reports of successful STO growth on Si substrates using pulsed laser deposi- tion [7–9], electron-beam (e-beam) deposition [10,11] and molecular beam epitaxy [12–15]. SrO buffer layer has been proposed for the epitaxial growth of STO films on Si(0 0 1) substrates [10,15,16]. Furthermore, the growths of a superconducting YBa 2 Cu 3 O 7x and Applied Surface Science 216 (2003) 590–595 * Corresponding author. Tel.: þ81-76-445-6728; fax: þ81-76-445-6728. E-mail address: d013014@ems.toyama-u.ac.jp (M.N.K. Bhuiyan). 0169-4332/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0169-4332(03)00452-5