Description:

The Department of Materials Science and Engineering welcomes you to its 2014 Fall Colloquium Series.

Location: Tech L361, 4:00pm

Chris Van de Walle
Professor, Materials Department
University of California Santa Barbara

Effects of High Doping in Transparent Conductors
Basic information about transparent conductors, particularly about doping and how it affects electronic and optical properties, is often lacking. First-principles calculations are now capable of accurately predicting quantities that are directly relevant for applications. In oxides that can be highly doped, the large carrier concentrations significantly affect optical transparency. While direct absorption (either across the gap or to higher-lying conduction bands) is usually not a problem, indirect processes assisted by electron-phonon scattering create absorption, sometimes with unexpected wavelength dependence. First-principles evaluations of free-carrier absorption provide insight into the factors that limit this key criterion for transparent conducting oxides. The presence of large concentrations of electrons in the conduction band also affects the absorption edge, not only because of conduction-band filling but also through band-gap renormalization. I will discuss these processes and how we can treat them consistently and in quantitative detail.
Biography:
Chris Van de Walle is the inaugural recipient of the Herbert Kroemer Endowed Chair in Materials Science at the University of California, Santa Barbara. Van de Walle develops and employs first-principles computational techniques to model the structure and behavior of materials. He has performed extensive studies of semiconductor interfaces (including the development of a widely used model for band offsets) and of defects and impurities in semiconductors, with particular emphasis on doping problems. In recent years he has been focusing his attention on wide-band-gap semiconductors, nitrides, oxides, on the behavior of hydrogen in materials, and on spin centers for quantum computing. He co-leads IRG-2, “Correlated Electronics”, in the UCSB MRSEC, and his group is actively engaged in studies of efficiency limits in light emitters, novel channel materials for CMOS, transparent conducting oxides, and hydrogen storage materials. He has published over 350 research papers, holds 23 patents, has given 150 invited and plenary talks at international conferences, and is included in the 2014 “Highly Cited Researchers” list (www.highlycited.com). Professor Van de Walle has chaired three conferences, and was Program Chair for the 27th International Conference on the Physics of Semiconductors in 2004. He is a Fellow of the APS, AVS, AAAS, MRS, and IEEE, as well as the recipient of a Humboldt Award for Senior US Scientist, the David Adler Award from the APS, and the Medard W. Welch Award from the AVS.

Before joining the UCSB Materials Department in 2004, Professor Van de Walle was a Principal Scientist in the Electronic Materials Laboratory at the Xerox Palo Alto Research Center (PARC). He received his Ph.D. in Electrical Engineering from Stanford University in 1986. He was a postdoctoral scientist at the IBM T. J. Watson Research Center in Yorktown Heights, New York (1986-1988), a Senior Member of Research Staff at Philips Laboratories in Briarcliff Manor, New York (1988-1991), and an Adjunct Professor of Materials Science at Columbia University (1991).