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Title: Defects, stoichiometry, and electronic transport in SrTiO{sub 3-δ} epilayers: A high pressure oxygen sputter deposition study

Abstract

SrTiO{sub 3} is not only of enduring interest due to its unique dielectric, structural, and lattice dynamical properties, but is also the archetypal perovskite oxide semiconductor and a foundational material in oxide heterostructures and electronics. This has naturally focused attention on growth, stoichiometry, and defects in SrTiO{sub 3}, one exciting recent development being such precisely stoichiometric defect-managed thin films that electron mobilities have finally exceeded bulk crystals. This has been achieved only by molecular beam epitaxy, however (and to a somewhat lesser extent pulsed laser deposition (PLD)), and numerous open questions remain. Here, we present a study of the stoichiometry, defects, and structure in SrTiO{sub 3} synthesized by a different method, high pressure oxygen sputtering, relating the results to electronic transport. We find that this form of sputter deposition is also capable of homoepitaxy of precisely stoichiometric SrTiO{sub 3}, but only provided that substrate and target preparation, temperature, pressure, and deposition rate are carefully controlled. Even under these conditions, oxygen-vacancy-doped heteroepitaxial SrTiO{sub 3} films are found to have carrier density, mobility, and conductivity significantly lower than bulk. While surface depletion plays a role, it is argued from particle-induced X-ray emission (PIXE) measurements of trace impurities in commercial sputtering targets thatmore » this is also due to deep acceptors such as Fe at 100's of parts-per-million levels. Comparisons of PIXE from SrTiO{sub 3} crystals and polycrystalline targets are shown to be of general interest, with clear implications for sputter and PLD deposition of this important material.« less

Authors:
; ; ; ; ; ;  [1];  [2]
  1. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
  2. Characterization Facility, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
Publication Date:
OSTI Identifier:
22597695
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 5; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CARRIER DENSITY; DEFECTS; DIELECTRIC MATERIALS; DOPED MATERIALS; ELECTRON MOBILITY; ENERGY BEAM DEPOSITION; LASER RADIATION; MOLECULAR BEAM EPITAXY; MOLECULAR BEAMS; OXIDES; OXYGEN; PEROVSKITE; PIXE ANALYSIS; POLYCRYSTALS; PULSED IRRADIATION; SPUTTERING; STOICHIOMETRY; STRONTIUM TITANATES; THIN FILMS

Citation Formats

Ambwani, P., Xu, P., Jeong, J. S., Deng, R., Mkhoyan, K. A., Jalan, B., Leighton, C., E-mail: leighton@umn.edu, and Haugstad, G. Defects, stoichiometry, and electronic transport in SrTiO{sub 3-δ} epilayers: A high pressure oxygen sputter deposition study. United States: N. p., 2016. Web. doi:10.1063/1.4960343.
Ambwani, P., Xu, P., Jeong, J. S., Deng, R., Mkhoyan, K. A., Jalan, B., Leighton, C., E-mail: leighton@umn.edu, & Haugstad, G. Defects, stoichiometry, and electronic transport in SrTiO{sub 3-δ} epilayers: A high pressure oxygen sputter deposition study. United States. doi:10.1063/1.4960343.
Ambwani, P., Xu, P., Jeong, J. S., Deng, R., Mkhoyan, K. A., Jalan, B., Leighton, C., E-mail: leighton@umn.edu, and Haugstad, G. Sun . "Defects, stoichiometry, and electronic transport in SrTiO{sub 3-δ} epilayers: A high pressure oxygen sputter deposition study". United States. doi:10.1063/1.4960343.
@article{osti_22597695,
title = {Defects, stoichiometry, and electronic transport in SrTiO{sub 3-δ} epilayers: A high pressure oxygen sputter deposition study},
author = {Ambwani, P. and Xu, P. and Jeong, J. S. and Deng, R. and Mkhoyan, K. A. and Jalan, B. and Leighton, C., E-mail: leighton@umn.edu and Haugstad, G.},
abstractNote = {SrTiO{sub 3} is not only of enduring interest due to its unique dielectric, structural, and lattice dynamical properties, but is also the archetypal perovskite oxide semiconductor and a foundational material in oxide heterostructures and electronics. This has naturally focused attention on growth, stoichiometry, and defects in SrTiO{sub 3}, one exciting recent development being such precisely stoichiometric defect-managed thin films that electron mobilities have finally exceeded bulk crystals. This has been achieved only by molecular beam epitaxy, however (and to a somewhat lesser extent pulsed laser deposition (PLD)), and numerous open questions remain. Here, we present a study of the stoichiometry, defects, and structure in SrTiO{sub 3} synthesized by a different method, high pressure oxygen sputtering, relating the results to electronic transport. We find that this form of sputter deposition is also capable of homoepitaxy of precisely stoichiometric SrTiO{sub 3}, but only provided that substrate and target preparation, temperature, pressure, and deposition rate are carefully controlled. Even under these conditions, oxygen-vacancy-doped heteroepitaxial SrTiO{sub 3} films are found to have carrier density, mobility, and conductivity significantly lower than bulk. While surface depletion plays a role, it is argued from particle-induced X-ray emission (PIXE) measurements of trace impurities in commercial sputtering targets that this is also due to deep acceptors such as Fe at 100's of parts-per-million levels. Comparisons of PIXE from SrTiO{sub 3} crystals and polycrystalline targets are shown to be of general interest, with clear implications for sputter and PLD deposition of this important material.},
doi = {10.1063/1.4960343},
journal = {Journal of Applied Physics},
number = 5,
volume = 120,
place = {United States},
year = {Sun Aug 07 00:00:00 EDT 2016},
month = {Sun Aug 07 00:00:00 EDT 2016}
}
  • Cited by 2
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  • In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO 3 (STO) thin films onmore » single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Thus, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but it expands the utility of pulsed laser epitaxy of other materials as well.₃« less