Mechanism of polarization switching in wurtzite-structured zinc oxide thin films

Journal Article · Mon Sep 05 00:00:00 EDT 2016 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4962440· OSTI ID:22594296

Konishi, Ayako; Ogawa, Takafumi; Fisher, Craig A. J.; Kuwabara, Akihide; Moriwake, Hiroki ^[1]; Shimizu, Takao; Yasui, Shintaro; Itoh, Mitsuru ^[2]

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1. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587 (Japan)
2. Materials and Structures Laboratory, Tokyo Institute Technology, Yokohama 226-8503 (Japan)

The properties of a potentially new class of ferroelectric materials based on wurtzite-structured ZnO thin films are examined using the first-principles calculations. Theoretical P-E hysteresis loops were calculated using the fixed-D method for both unstrained and (biaxially) strained single crystals. Ferroelectric polarization switching in ZnO (S.G. P6{sub 3}mc) is shown to occur via an intermediate non-polar structure with centrosymmetric P6{sub 3}/mmc symmetry by displacement of cations relative to anions in the long-axis direction. The calculated coercive electric field (E{sub c}) for polarization switching was estimated to be 7.2 MV/cm for defect-free monocrystalline ZnO. During switching, the short- and long-axis lattice parameters expand and contract, respectively. The large structural distortion required for switching may explain why ferroelectricity in this compound has not been reported experimentally for pure ZnO. Applying an epitaxial tensile strain parallel to the basal plane is shown to be effective in lowering E{sub c} during polarization, with a 5% biaxial expansion resulting in a decrease of E{sub c} to 3.5 MV/cm. Comparison with calculated values for conventional ferroelectric materials suggests that the ferroelectric polarization switching of wurtzite-structured ZnO may be achievable by preparing high-quality ZnO thin films with suitable strain levels and low defect concentrations.

• OSTI ID: 22594296
• Journal Information: Applied Physics Letters, Vol. 109, Issue 10; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANIONS
CATIONS
COMPARATIVE EVALUATIONS
DEFECTS
ELECTRIC FIELDS
EPITAXY
FERROELECTRIC MATERIALS
HCP LATTICES
LATTICE PARAMETERS
MONOCRYSTALS
POLARIZATION
STRAINS
SYMMETRY
THIN FILMS
ZINC OXIDES