Homoepitaxial Growth of SrTiO3 in an Ultrahigh Vacuum with Automatic Feeding of Oxygen from the Substrate at Temperatures as Low as 370°C

Abstract

Homoepitaxial growth of SrTiO 3 without introducing any oxidants has been achieved at low temperatures. The growth was carried out by coevaporation of Sr and Ti metals under extremely low oxygen partial pressure ( pO 2 < 1 × 10 −8 Pa). A clear reflection high-energy electron diffraction (RHEED) intensity oscillation from the layer-by-layer growth of SrTiO 3 was observed during the growth at a substrate temperature of 370 • C. The deposited film was found to have an approximately stoichiometric composition and a single-phase of SrTiO 3 , from the analyses of Auger electron spectroscopy (AES) and RHEED. Oxygen was automatically fed from the substrate to the growing surface. Instead, oxygen vacancies were incorporated into the bulk of the substrate. The incorporated oxygen vacancies were evaluated by positron annihilation.

Suppression of oxygen diffusion by thin Al2O3 films grown on SrTiO3 studied using a monoenergetic positron beam

“…The details of the growth method for metal-oxide films on SrTiO 3 substrates are given elsewhere. 19,21 Before the film growth, the substrates were annealed in an O 2 atmosphere for 1 h at 1050-1100°C, and the films were then grown by evaporating metals (Sr, Ti, and Al). During the growth process, the oxygen partial pressure was less than 1 ϫ 10 −8 Pa.…”

“…Thus, we call this deposition technique "automatic feeding epitaxy" (AFE). 21 For the SrTiO 3 / SrTiO 3 samples, the substrate conductivity was measured by applying a standard dc four-probe technique at room temperature. Al 2 O 3 films were deposited on both sides of the substrates (sample structure: Al 2 O 3 / SrTiO 3 /Al 2 O 3 ) to prevent oxygen penetration from the backside of the sample during annealing.…”

Study of oxygen vacancies in SrTiO3 by positron annihilation

“…Details of the growth method are given elsewhere. 16,17 The substrates were supplied by Shinkosha Co., Ltd., and they were grown with ͑100͒ orientation by the Verneuil method. The substrates were annealed in an O 2 atmosphere for 1 h at 1050-1100°C, and then the SrTiO 3 films were grown epitaxially by coevaporation of Sr and Ti.…”

“…17 No oscillation, but monotonous deterioration of the RHEED pattern was observed during the growth at 280°C ͑the pattern was a halo͒. This indicates that the film is amorphous.…”

“…Shimoyama and co-workers 16,17 reported that BaTiO 3 or SrTiO 3 films can be epitaxially grown on SrTiO 3 substrates by supplying only metal atoms. In their study, an intensity oscillation of RHEED spots from layer-by-layer growth was clearly observed during the growth of the film.…”