Tuning the properties of complex transparent conducting oxides: role of crystal symmetry, chemical composition and carrier generation

Abstract

The electronic properties of single- and multi-cation transparent conducting oxides (TCOs) are investigated using first-principles density functional approach. A detailed comparison of the electronic band structure of stoichiometric and oxygen deficient In${}_2$O${}_3$, $\alpha$- and $\beta$-Ga${}_2$O${}_3$, rock salt and wurtzite ZnO, and layered InGaZnO${}_4$ reveals the role of the following factors which govern the transport and optical properties of these TCO materials: (i) the crystal symmetry of the oxides, including both the oxygen coordination and the long-range structural anisotropy; (ii) the electronic configuration of the cation(s), specifically, the type of orbital(s) -- $s$, $p$ or $d$ -- which form the conduction band; and (iii) the strength of the hybridization between the cation's states and the p-states of the neighboring oxygen atoms. The results not only explain the experimentally observed trends in the electrical conductivity in the single-cation TCO, but also demonstrate that multicomponent oxides may offer a way to overcome the electron localization bottleneck which limits the charge transport in wide-bandgap main-group metal oxides. Further, the advantages of aliovalent substitutional doping -- an alternative route to generate carriers in a TCO host -- are outlined based on the electronic band structure calculations of Sn, Ga, Ti and Zr-doped InGaZnO${}_4$. We show that the transition metal dopants offer a possibility to improve conductivity without compromising the optical transmittance.

References in corpus (3)

• Magnetically Mediated Transparent Conductors: In${}_2$O${}_3$ doped with Mo
• Averaging of the electron effective mass in multicomponent transparent conducting oxides
• Electronic band structure and carrier effective mass in calcium aluminates

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• Electron effective mass and electronic structure in nonstoichiometric a-IGZO films
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