title: Enhanced thermopower in ZnO two-dimensional electron gas.
abstract: Control of dimensionality has proven to be an effective way to manipulate the electronic properties of materials, thereby enabling exotic quantum phenomena, such as superconductivity, quantum Hall effects, and valleytronic effects. Another example is thermoelectricity, which has been theoretically proposed to be favorably controllable by reducing the dimensionality. Here, we verify this proposal by performing a systematic study on a gate-tuned 2D electron gas (2DEG) system formed at the surface of ZnO. Combining state-of-the-art electric-double-layer transistor experiments and realistic tight-binding calculations, we show that, for a wide range of carrier densities, the 2DEG channel comprises a single subband, and its effective thickness can be reduced to [Formula: see text] 1 nm at sufficiently high gate biases. We also demonstrate that the thermoelectric performance of the 2DEG region is significantly higher than that of bulk ZnO. Our approach opens up a route to exploit the peculiar behavior of 2DEG electronic states and realize thermoelectric devices with advanced functionalities.
authors.affiliation: RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan; sshimizu@riken.jp.
authors.forename: Sunao
authors.initials: S
authors.lastname: Shimizu
authors.affiliation: RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan; Quantum Phase Electronics Center and Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan;
authors.forename: Mohammad Saeed
authors.initials: MS
authors.lastname: Bahramy
authors.affiliation: Quantum Phase Electronics Center and Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan;
authors.forename: Takahiko
authors.initials: T
authors.lastname: Iizuka
authors.affiliation: RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan; Central Research Institute of Electric Power Industry, Yokosuka, Kanagawa 240-0196, Japan.
authors.forename: Shimpei
authors.initials: S
authors.lastname: Ono
authors.affiliation: Central Research Institute of Electric Power Industry, Yokosuka, Kanagawa 240-0196, Japan.
authors.forename: Kazumoto
authors.initials: K
authors.lastname: Miwa
authors.affiliation: RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan; Quantum Phase Electronics Center and Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan;
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Tokura
authors.affiliation: RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan; Quantum Phase Electronics Center and Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan;
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Iwasa
mesh_terms: D004560:Electricity; D004583:Electrons; D005740:Gases; D006358:Hot Temperature; D008962:Models, Theoretical; D012666:Semiconductors; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D005740:Gases; D015034:Zinc Oxide
keywords: Seebeck effect; electric-double-layer transistor; field effect; two-dimensional electron gas