EuO epitaxy by oxygen scavenging on SrTiO3 (001): Effect of SrTiO3 thickness and temperature

• Published in: Journal of applied physics 2018-12, Vol.124 (23)
• Main Authors: Guo, Wei, Posadas, Agham B., Lu, Sirong, Smith, David J., Demkov, Alexander A.
• Format: Article
• Language: English
• Subjects: Applied physics; Crystal structure; Deposition; Electronic structure; Ferromagnetic materials; Heterojunctions; High temperature; Interlayers; Oxygen; Photoelectrons; Scavenging; Silicon substrates; Strontium titanates; Thickness; Ultrahigh vacuum
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5059560

The EuO/SrTiO3 heterojunction is a promising combination of a ferromagnetic material and a two-dimensional electron system. We explore the deposition of Eu metal on SrTiO3/Si pseudo-substrates, with varying SrTiO3 (STO) thickness, under ultrahigh vacuum conditions. By varying the thickness of the STO layer (2-10 nm) and the deposition temperature (20-300 °C), we investigate the process by which oxygen is scavenged from STO by Eu. In situ x-ray photoelectron spectroscopy is used to investigate the electronic structure of the nominal Eu/STO/Si stack. We find that as a result of Eu deposition, epitaxial EuO is formed on thick STO (6-10 nm), leaving behind a highly oxygen-deficient SrTiO3-δ layer of ∼4 nm in thickness. However, if the thickness of the STO layer is comparable to or less than the scavenging depth, the crystal structure of STO is disrupted and a solid state reaction between Eu, Si, and STO occurs when the deposition is done at a high temperature (300 °C). On the other hand, at a low temperature (20 °C), only a 1-2 nm-thick EuO interlayer is grown, on top of which the Eu metal appears to be stable. This study elucidates the growth process under different conditions and provides a better understanding and control of this system.