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A chemically driven insulator–metal transition in non-stoichiometric and amorphous gallium oxide

Nature Materials volume 7, pages 391–398 (2008)Cite this article

Abstract

Insulator–metal transitions are well known in transition-metal oxides, but inducing an insulator–metal transition in the oxide of a main group element is a major challenge. Here, we report the observation of an insulator–metal transition, with a conductivity jump of seven orders of magnitude, in highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO1.2 at a temperature around 670 K. We demonstrate through experimental studies and density-functional-theory calculations that the conductivity jump takes place at a critical gallium concentration and is induced by crystallization of stoichiometric Ga2O3 within the metastable oxide matrix—in chemical terms by a disproportionation. This novel mechanism—an insulator–metal transition driven by a heterogeneous solid-state reaction—opens up a new route to achieve metallic behaviour in oxides that are expected to exist only as classic insulators.

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Figure 1: Electrical conductivity of gallium oxide films prepared by PLD.
Figure 2: Structure of gallium oxide films, Ga0.45O0.55, prepared by PLD in argon atmosphere.
Figure 3: DOS and electron density distribution for gallium oxide with small gallium excess.
Figure 4: Electronic structure of supercells Ga20O24, Ga22O24 and Ga24O24.
Figure 5: In situ optical absorption of a gallium oxide film deposited in nitrogen.
Figure 6: Schematic description of the correlation between geometrical structure, gallium excess, electrical conductivity and band structure of highly non-stoichiometric, amorphous gallium oxide as a function of temperature.

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Acknowledgements

We gratefully acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) within the Priority Program 1136. We thank J. Rodesch for carrying out preliminary measurements; R. Dronskowski for allowing us to use the Quantum Design PPMS; HASYLAB for the provision of beam time and travel funding; E. Welter, W. Calibe, J. Brendt, D. Müller and D. Röhrens for support during the X-ray absorption spectroscopy measurements; and T. Weirich for the TEM measurements.

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Authors and Affiliations

  1. Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany

    Lakshmi Nagarajan, Roger A. De Souza, Dominik Samuelis & Manfred Martin

  2. Institute of Physical Chemistry, Justus Liebig University, 35392 Giessen, Germany

    Ilia Valov & Jürgen Janek

  3. Institute of Physical and Theoretical Chemistry, Technical University of Braunschweig, 38106 Braunschweig, Germany

    Alexander Börger & Klaus-Dieter Becker

  4. Institute of Physical Chemistry, Technical University of Darmstadt, 64287 Darmstadt, Germany

    Peter C. Schmidt

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  1. Lakshmi Nagarajan
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Correspondence to Manfred Martin.

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Nagarajan, L., De Souza, R., Samuelis, D. et al. A chemically driven insulator–metal transition in non-stoichiometric and amorphous gallium oxide. Nature Mater 7, 391–398 (2008). https://doi.org/10.1038/nmat2164

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