The electronic properties of single- and multication 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 ${\text{In}}_2{\text{O}}_3$, $\alpha$, and $\beta {\text{-Ga}}_2{\text{O}}_3$, rock salt and wurtzite ZnO, and layered ${\text{InGaZnO}}_4$ 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 band-gap 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 ${\text{InGaZnO}}_4$. We show that the transition metal dopants offer a possibility to improve conductivity without compromising the optical transmittance.

• Received 18 December 2009

DOI:https://doi.org/10.1103/PhysRevB.81.125116