Abstract
A highly conductive metallic gas that is quantum mechanically confined at a solid-state interface is an ideal platform to explore non-trivial electronic states that are otherwise inaccessible in bulk materials. Although two-dimensional electron gases have been realized in conventional semiconductor interfaces, examples of two-dimensional hole gases, the counterpart to the two-dimensional electron gas, are still limited. Here we report the observation of a two-dimensional hole gas in solution-processed organic semiconductors in conjunction with an electric double layer using ionic liquids. A molecularly flat single crystal of high-mobility organic semiconductors serves as a defect-free interface that facilitates two-dimensional confinement of high-density holes. A remarkably low sheet resistance of 6âkΩ and high hole-gas density of 1014âcmâ2 result in a metalâinsulator transition at ambient pressure. The measured degenerate holes in the organic semiconductors provide an opportunity to tailor low-dimensional electronic states using molecularly engineered heterointerfaces.
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We declare that all data supporting the findings of this study are included within the paper and its Supplementary Information files. Source data are provided with this paper.
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Acknowledgements
S.W. acknowledges the support from the Leading Initiative for Excellent Young Researchers of JSPS. T.O. acknowledges the support from PRESTO-JST through the project âScientific Innovation for Energy Harvesting Technologyâ (grant no. JPMJPR17R2). This work was supported by Kakenhi Grants-in-Aid (nos. JP17H06123, JP17H06200, 20H00387) from JSPS, and JST FOREST Program, grant no. JPMJFR2020.
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N.K. conceived, designed and performed the experiments and analysed the data. N.K. and J. Tsurumi performed the density functional theory calculations. T.O. synthesized and purified C8-DNBDT-NW. N.K., S.W. and J. Takeya wrote the manuscript. S.W. and J. Takeya supervised the work. All authors discussed the results and reviewed the manuscript.
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Supplementary Information
Supplementary Figs. A1âD1, Notes AâD and references.
Source data
Source Data Fig. 2
Currentâvoltage characteristics, gate voltage dependent carrier density and Hall mobility derived from the Hall effect measurements.
Source Data Fig. 3
Temperature dependence of sheet resistance.
Source Data Fig. 4
Temperature dependence of Hall mobility and carrier density.
Source Data in Supplementary information
Sample variation in currentâvoltage characteristics and magnetotransports.
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Kasuya, N., Tsurumi, J., Okamoto, T. et al. Two-dimensional hole gas in organic semiconductors. Nat. Mater. 20, 1401â1406 (2021). https://doi.org/10.1038/s41563-021-01074-4
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DOI: https://doi.org/10.1038/s41563-021-01074-4
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