Study of epitaxial SrTiO 3 (STO) thin films grown on Si(0 0 1)–2 × 1 substrates by molecular beam epitaxy

Abstract

Perovskite-type oxide SrTiO 3 (STO) thin films with thicknesses of 30, 100, 300 and 1000 Å 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 °C by molecular beam epitaxy (MBE). SrO buffer layers of 100 Å have been grown at 350 °C 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 °C 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 Å-thick STO films. On the contrary, spotty and streaky patterns, and spotty patterns are observed clearly for 300 and 1000 Å-thick films, respectively. The surface crystallinity improves for all the samples after annealing at 800 °C. The STO films with thicknesses of 30 and 1000 Å consist of grains in the images of atomic force microscopy. The flatness and crystallinity of STO films with the thickness of 100–300 Å are better than the other films.