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

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

J. B. Varley, A. Janotti, C. Franchini, and C. G. Van de Walle

Phys. Rev. B 85, 081109(R) – Published 27 February 2012

Abstract

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 $_{2}$ . Based on hybrid functional calculations, 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. We demonstrate that polaron formation prohibits $p$ -type conductivity in this class of materials.

Received 21 January 2012

DOI:https://doi.org/10.1103/PhysRevB.85.081109

Authors & Affiliations

J. B. Varley¹, A. Janotti², C. Franchini³, and C. G. Van de Walle²

¹Department of Physics, University of California, Santa Barbara, California 93106-9530, USA
²Materials Department, University of California, Santa Barbara, California 93106-5050, USA
³Faculty of Physics, University of Vienna and Center for Computational Materials Science, A-1090 Vienna, Austria

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Issue

Vol. 85, Iss. 8 — 15 February 2012

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