Electrolyte-gate-driven carrier density modulation and metal-insulator transition in semiconducting epitaxial CdO films

Helin Wang, William M. Postiglione, Vipul Chaturvedi, Evan L. Runnerstrom, Angela Cleri, Josh Nordlander, Jon-paul Maria, Chris Leighton

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CdO has drawn much recent interest as a high-room-temperature-mobility oxide semiconductor with exciting potential for mid-infrared photonics and plasmonics. Wide-range modulation of carrier density in CdO is of interest both for fundamental reasons (to explore transport mechanisms in single samples) and for applications (in tunable photonic devices). Here, we thus apply ion-gel-based electrolyte gating to ultrathin epitaxial CdO(001) films, using transport, x-ray diffraction, and atomic force microscopy to deduce a reversible electrostatic gate response from -4 to +2 V, followed by rapid film degradation at higher gate voltage. Further advancing the mechanistic understanding of electrolyte gating, these observations are explained in terms of low oxygen vacancy diffusivity and high acid etchability in CdO. Most importantly, the 6-V-wide reversible electrostatic gating window is shown to enable ten-fold modulation of the Hall electron density, a striking voltage-induced metal-insulator transition, and 15-fold variation of the electron mobility. Such modulations, which are limited only by unintentional doping levels in ultrathin films, are of exceptional interest for voltage-tunable devices.

Original languageEnglish (US)
Article number121106
Pages (from-to)121106
JournalAPL Materials
Issue number12
StatePublished - Dec 1 2022

Bibliographical note

Funding Information:
Work at the University of Minnesota (UMN) was primarily supported by the National Science Foundation (NSF) through the UMN MRSEC under Grant No. DMR-2011401. Parts of this work were carried out at the Characterization Facility, UMN, which receives partial support from the NSF through the MRSEC program. Portions of this work were also conducted in the Minnesota Nano Center, which is supported by the NSF through the National Nanotechnology Coordinated Infrastructure under Grant No. ECCS-2025124. Work at Pennsylvania State University was supported by the Office of Naval Research Grant No. N00014-22-12035, Army Research Office Research Grant No. W911NF-16-1-0406, and the Department of Defense (DoD) through the National Defense Science and Engineering Graduate (NDSEG) Fellowship Program.

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© 2022 Author(s).

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