Role of self-trapping in luminescence and $p$-type conductivity of wide-band-gap oxides

ORAL

Abstract

Using hybrid functional calculations, we investigate the behavior of holes in the valence band of a range of wide-band-gap oxides including ZnO, MgO, In$_2$O$_3$, Ga$_2$O$_3$, Al$_2$O$_3$, SnO$_2$, SiO$_2$, and TiO$_2$. We find that, due to the orbital composition of the valence band, holes tend to form localized small polarons with characteristic lattice distortions, even in the absence of defects or impurities. These self-trapped holes (STHs) are energetically more favorable than delocalized, free holes in the valence band in all materials but ZnO and SiO$_2$. Based on calculated optical absorption and emission energies we show that STHs provide an explanation for the luminescence peaks that have been observed in many of these oxides. Additionally, we demonstrate that polaron formation prohibits $p$-type conductivity in this class of materials.

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Authors

  • Joel Varley

    Materials Department, University of California Santa Barbara, Stanford University

  • Anderson Janotti

    Materials Department, University of California Santa Barbara, University of California, Santa Barbara Materials Department, University of California Santa Barbara, University of California, Santa Barbara

  • Cesare Franchini

    University of Vienna and Center for Computational Materials Science

  • Chris Van de Walle

    University of California at Santa Barbara, Materials Department, University of California, Santa Barbara, Materials Department, University of California Santa Barbara, University of California, Santa Barbara, University of California, Santa Barbara Materials Department, University of California Santa Barbara, Materials department and materials Research Lab, University of California Santa Barbara, California 93106-5050, USA, Materials Department, University of California at Santa Barbara