Manipulation of polycrystalline TiO2 carrier concentration via electrically active native defects

Sellers, Meredith C. K.; Seebauer, Edmund G.

doi:doi:10.1116/1.3635373

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Journal of Vacuum Science & Technology A / Volume 29 / Issue 6 / Thin Films

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J. Vac. Sci. Technol. A 29, 061503 (2011); http://dx.doi.org/10.1116/1.3635373 (8 pages)

Manipulation of polycrystalline TiO₂ carrier concentration via electrically active native defects

Meredith C. K. Sellers and Edmund G. Seebauer

Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801

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(Published online 14 September 2011)

Abstract

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There is good reason to believe that the properties of semiconducting metal oxides for catalytic applications can be improved when designed according to the principles of microelectronic devices. Nevertheless, defect engineering of polycrystalline TiO₂ is complicated by native charged point defects and grain boundaries that alter bulk carrier concentration in a manner that depends on synthesis and post-treatment protocols. These influences are difficult to decouple with standard electrical characterization methods, which typically induce rectifying Schottky barriers to wide-bandgap semiconductors like TiO₂. Here, TiO₂ donor carrier concentration (N_d) is investigated as a function of film thickness and annealing time using a rigorous Schottky diode-based electrical characterization approach. N_d scales inversely with film thickness due to a reduction in the concentration of electrically active grain boundaries in the bulk. Annealing of polycrystalline TiO₂ at 550 °C induces film densification that reduces the void volume surface area available for charge trapping. Strategies for defect engineering polycrystalline metal oxides must focus on tuning electrical activity of grain boundaries and intergranular voids for successful control and manipulation of N_d.

ACKNOWLEDGMENTS

This work was carried out in part at the Center for Microanalysis of Materials at the Frederick Seitz Materials Research Laboratory, University of Illinois, which is partially supported by the U.S. Department of Energy (DE-FG02-07ER46453 and DE-FG02-07ER46471) and by the National Science Foundation. The authors acknowledge funding from the National Science Foundation through a Graduate Research Fellowship (M.C.K.S.) and Grant No. DMR 07-04354. The authors are grateful for the assistance of Mauro Sardela, Rick Haasch, Dane Sievers, and Edmond Chow.

Article Outline

INTRODUCTION
EXPERIMENT
1. Preparation of polycrystalline TiO ₂ films
2. Film characterization and analysis
RESULTS
1. Chemical composition
2. Crystallinity and morphology
3. Influence of film thickness on carrier concentration
4. Influence of annealing time on carrier concentration
DISCUSSION
CONCLUSION

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KEYWORDS and PACS

Keywords

annealing, carrier density, catalysts, densification, grain boundaries, interstitials, rectification, Schottky barriers, semiconductor materials, semiconductor thin films, titanium compounds, voids (solid), wide band gap semiconductors

PACS

73.61.Le

Other inorganic semiconductors
61.72.jj

Interstitials
68.55.-a

Thin film structure and morphology
61.72.Cc

Kinetics of defect formation and annealing
73.30.+y

Surface double layers, Schottky barriers, and work functions
61.72.Mm

Grain and twin boundaries
61.72.Qq

Microscopic defects (voids, inclusions, etc.)

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History

Received 14 May 2011
Accepted 19 August 2011
Published online 14 September 2011

Digital Object Identifier

http://dx.doi.org/10.1116/1.3635373

PUBLICATION DATA

ISSN

0734-2101 (print)

1520-8559 (online)

Publisher

American Vacuum Society

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