Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates

• Published in: Journal of applied physics 2014-06, Vol.115 (22)
• Main Authors: McDaniel, Martin D., Posadas, Agham, Ngo, Thong Q., Karako, Christine M., Bruley, John, Frank, Martin M., Narayanan, Vijay, Demkov, Alexander A., Ekerdt, John G.
• Format: Article
• Language: English
• Subjects: Annealing; Applied physics; Atomic layer epitaxy; Barium titanates; Buffers; Crystal structure; Crystallinity; Electron diffraction; Energy transmission; Epitaxial growth; Ferroelectric materials; Ferroelectricity; Field effect transistors; Heterostructures; Lanthanum; Molecular beam epitaxy; Molecular structure; Semiconductor devices; Silicon substrates; Strontium titanates; Thin films; Transmission electron microscopy; X ray reflection; X-ray diffraction
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4883767

Strontium titanate, SrTiO3 (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5–25 nm. Atomic layer deposition (ALD) is used to grow the LaxSr1−xTiO3 (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (∼225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ∼2.0 × 10−2 Ω cm for 20-nm-thick La:STO (x ∼ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO3 integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.