High-Density Carrier Accumulation in ZnO Field-Effect Transistors Gated by Electric Double Layers of Ionic Liquids

Authors

  • Hongtao Yuan,

    Corresponding author
    1. Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
    2. Japan Science and Technology Agency (CREST) Kawaguchi 332-0012, Japan
    • Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan).
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  • Hidekazu Shimotani,

    1. Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
    2. Japan Science and Technology Agency (CREST) Kawaguchi 332-0012, Japan
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  • Atsushi Tsukazaki,

    1. Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
    2. Japan Science and Technology Agency (CREST) Kawaguchi 332-0012, Japan
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  • Akira Ohtomo,

    1. Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
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  • Masashi Kawasaki,

    1. Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
    2. Japan Science and Technology Agency (CREST) Kawaguchi 332-0012, Japan
    3. WPI Advanced Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
    4. Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
    5. Japan Science and Technology Agency (CREST) Kawaguchi 332-0012, Japan
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  • Yoshihiro Iwasa

    1. Institute for Materials Research, Tohoku University Sendai 980-8577 (Japan)
    2. Japan Science and Technology Agency (CREST) Kawaguchi 332-0012, Japan
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Abstract

Very recently, electric-field-induced superconductivity in an insulator was realized by tuning charge carrier to a high density level (1 × 1014 cm−2). To increase the maximum attainable carrier density for electrostatic tuning of electronic states in semiconductor field-effect transistors is a hot issue but a big challenge. Here, ultrahigh density carrier accumulation is reported, in particular at low temperature, in a ZnO field-effect transistor gated by electric double layers of ionic liquid (IL). This transistor, called an electric double layer transistor (EDLT), is found to exhibit very high transconductance and an ultrahigh carrier density in a fast, reversible, and reproducible manner. The room temperature capacitance of EDLTs is found to be as large as 34 µF cm−2, deduced from Hall-effect measurements, and is mainly responsible for the carrier density modulation in a very wide range. Importantly, the IL dielectric, with a supercooling property, is found to have charge-accumulation capability even at low temperatures, reaching an ultrahigh carrier density of 8×1014 cm−2 at 220 K and maintaining a density of 5.5×1014 cm−2 at 1.8 K. This high carrier density of EDLTs is of great importance not only in practical device applications but also in fundamental research; for example, in the search for novel electronic phenomena, such as superconductivity, in oxide systems.

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