Invited Paper EM2-ThA3
The Role of Native Defects in the Electrical Conductivity of Metal-Oxide Semiconductors

Thursday, October 31, 2013, 2:40 pm, Room 101 B

Oxide semiconductors exist in a variety of crystal structures, exhibiting a wide range of bonding environments and electronic behavior. For instance, ZnO (wurtzite), In₂O₃ (bixbyite), and SnO₂ (rutile) all support high levels of n-type conductivity and are highly transparent to visible light, making them excellent transparent conductors. TiO₂ (rutile and anatase) and SrTiO₃ (STO, perovskite) are prototype wide-band-gap transition-metal oxides, widely studied for catalysis and, in the case of STO, often used as a substrate for high-T_c superconductors and other oxides. STO is also at the core of recently fabricated complex-oxide-based heterostructures that display two-dimensional electron gases (2DEGs) with high carrier densities. As in any semiconductor, native defects are expected to greatly influence the electronic properties of these oxides. In particular, oxygen vacancies have been invariably invoked as a source of unintentional n-type conductivity, based on annealing experiments. In this talk, the role of native defects in oxide semiconductors will be revisited from the perspective of first-principles calculations. The donor or acceptor character, the likelihood of defects to form as a function of Fermi-level position and chemical potential, and defect-related optical transitions will be discussed. The possibility of p-type doping will also be addressed.

This work was performed in collaboration with C. G. Van de Walle, J. L. Lyons, M. Choi, L. Bjaalie, and J. B. Varley, and supported by ARO and NSF.