Study of epitaxial SrTiO3 (STO) thin films grown on Si(001)-2 x 1 substrates by molecular beam epitaxy

Perovskite-type oxide SrTiO3 (STO) thin films with thicknesses of 30, 100, 300 and 1000 Angstrom 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 x 10(-8) Torr at 500 degreesC by molecular beam epitaxy (MBE). SrO buffer layers of 100 Angstrom have been grown at 350 degreesC on Si substrates. The SrTiO3 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 degreesC under Sr exposure for 2 min after the chemical cleaning and formation of protective SiO2 layer, RHEED patterns of the atomically clean Si(0 0 1)-2 x 1 surface have been observed. RHEED pattern becomes unclear after the growth of 30 and 100 Angstrom-thick STO films. On the contrary, spotty and streaky patterns, and spotty patterns are observed clearly for 300 and 1000 Angstrom-thick films, respectively. The surface crystallinity improves for all the samples after annealing at 800 degreesC. The STO films with thicknesses of 30 and 1000 Angstrom consist of grains in the images of atomic force microscopy. The flatness and crystallinity of STO films with the thickness of 100-300 Angstrom are better than the other films. (C) 2003 Elsevier Science B.V. All rights reserved.