Electronic and structural defects in transition-metal-oxide semiconductors

Date & Time
29 June 2012 (Fri), 16:00-17:00
4F room 409/410, Collaborative Bldg., Namiki site
Prof. Anderson Janotti
Materials Department, University of California, Santa Barbara
Electronic and structural defects in transition-metal-oxide semiconductors
There is great interest in developing transition-metal oxides such as TiO2 and SrTiO3 for semiconductor devices applications. As with any semiconductor, one of the main challenges in the early stages of development is to control the conductivity by doping and reducing the concentration of native defects and unintentional impurities, thus, minimizing their deleterious effects. These transition-metal oxides significantly differ from conventional semiconductors (Si, Ge, and GaAs) with respect to their electronic structure and charge transport. While in conventional semiconductors, electron and holes originated from doping are delocalized and result in high carrier mobility, excess electrons in TiO2 and SrTiO3 occupy degenerate conduction bands derived from Ti d states, leading to a variety of interesting physical phenomena; for instance, is often argued that transport in TiO2 occurs through hopping of small polarons, giving rise to rather low electron mobility. Here we will present results of density functional theory and hybrid functional for electronic and structural defects in TiO2 and SrTiO3. We will discuss the effects of charge localization in the form of small polarons in TiO2 and the consequences for optical and transport measurements. Shortcomings of the conventional density functional methods in describing charge localization will also be addressed.
Dr. Naoto Umezawa(梅澤直人)