Unintentional F doping of the surface of SrTiO3(001) etched in HF acid -- structure and electronic properties

Abstract

We show that the HF acid etch commonly used to prepare SrTiO3(001) for heteroepitaxial growth of complex oxides results in a non-negligible level of F doping within the terminal surface layer of TiO2. Using a combination of x-ray photoelectron spectroscopy and scanned angle x-ray photoelectron diffraction, we determine that on average ~13 % of the O anions in the surface layer are replaced by F, but that F does not occupy O sites in deeper layers. Despite this perturbation to the surface, the Fermi level remains unpinned, and the surface-state density, which determines the amount of band bending, is driven by factors other than F doping. The presence of F at the STO surface is expected to result in lower electron mobilities at complex oxide heterojunctions involving STO substrates because of impurity scattering. Unintentional F doping can be substantially reduced by replacing the HF-etch step with a boil in deionized water, which in conjunction with an oxygen tube furnace anneal, leaves the surface flat and TiO2 terminated.

18 pages, 7 figures

References in corpus (4)

• Unveiling a two-dimensional electron gas with universal subbands at the surface of SrTiO3
• Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface
• Instability, Intermixing and Electronic Structure at the Epitaxial LaAlO3/SrTiO3(001) Heterojunction
• Depth-Resolved Subsurface Defects in Chemically Etched SrTiO3

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• Interface-induced Polarization in SrTiO${}_3$-LaCrO${}_3$ Superlattices
• Does a pristine, unreconstructed SrTiO${}_3$(001) surface exist?
• Layer-resolved band bending at the n-SrTiO3(001)/p-Ge(001) interface
• Infrared Optical Absorption in Low-spin Fe${}^{2+}$-doped SrTiO${}_3$
• Observation by resonant angle-resolved photoemission of a critical thickness for 2-dimensional electron gas formation in SrTiO${}_3$ embedded in GdTiO${}_3$
• Conducting LaAlO3/SrTiO3 heterointerfaces on atomically flat substrates prepared by deionized-water