First-principles study of proton migration in indium oxide

Indium oxide is a semiconductor with a band gap of 2.68 eV, widely used as a transparent conducting oxide when doped with Sn. Previous work has shown that hydrogen also acts as a shallow donor [1]. Understanding diffusion of interstitial hydrogen is essential to control device properties such as conductivity and carrier density. As such, we investigate the migration of hydrogen in In₂O₃ using first-principles calculations based on density functional theory. We employ a hybrid functional to precisely describe the three possible charge states of hydrogen in the material and find that H⁺ (i.e., a proton) is most stable. We decompose the possible long-range migration paths of H⁺ into short-range mechanisms. Two mechanisms are involved in the motion of protons: rotations of the hydrogen atom around oxygen atoms and jumps between two oxygen atoms. We calculate the migration barrier heights using the nudged elastic band method. We establish that the jump between oxygen atoms is the rate-limiting step in the long-range migration mechanism, with an energy barrier of 0.8 eV.

[1] S. Limpijumnong et al., Phys. Rev. B 80, 193202 (2009).