NB-Photonics Seminar with prof. Chris Van de Walle

What: NB-Photonics seminar with prof. Chris Van de Walle (Materials Department, University of California, Santa Barbara, California, USA) on “Impact of Defects on Efficiency of Light Emitters”.

When: Monday 20th March 2017, 12.30 to 14.05

Where: LES 1.1 (1st floor), iGent, Campus Ardoyen – Zwijnaarde. For location and parking details see here.

** Registration is free but mandatory via this link **

12.30 – 13.00: Sandwich Lunch on ground floor of iGent Tower
13.00 – 13.05: Introduction by prof. Roel Baets
13.05 – 13.50: Seminar by prof. Chris Van de Walle
13.50 – 14.05: Discussion


Impact of Defects on Efficiency of Light Emitters

Nitride semiconductors are the key materials for solid-state lighting; they are also increasingly used for power electronics. For all these applications, high-quality material is essential. In both bulk crystals and epitaxial layers, point defects may act as compensating centers, charge traps, or radiative or nonradiative recombination centers. In addition, unintentional impurities often play an equally important role; for instance, carbon that is unavoidably incorporated during growth can act as a source of yellow luminescence.
I will discuss the theoretical advances that are enabling us to calculate the electronic and optical properties of point defects with unprecedented accuracy. I will focus on examples where defects limit device performance, although I will also touch upon cases where point defects provide functionality, for instance as single-photon sources, fluorescent biomarkers, or in metrology—a prominent example is the NV center in diamond.
Both point defects and impurities can affect the efficiency of light emitters, and we are actively pursuing the microscopic origins of nonradiative recombination. In spite of a long history (dating back to Shockley-Read-Hall), the quantitative evaluation of nonradiative recombination has proven very challenging. We have developed a first-principles methodology to determine carrier capture coefficients; all parameters in the theory, including electron-phonon coupling matrix elements, are computed consistently using state-of-the-art electronic structure techniques. Our approach allows us to identify specific defects in semiconductors that play a key role in limiting the efficiency of light-emitting diodes.
Work performed in collaboration with A. Alkauskas, C. Dreyer, A. Janotti, J. Lyons, J. Shen, D. Wickramaratne, and Q. Yan, and supported by DOE and NSF.


Biosketch of speaker

Chris Van de Walle (vandewalle@mrl.ucsb.edu) is the inaugural recipient of the Herbert Kroemer Endowed Chair in Materials Science and a Distinguished Professor of Materials at the University of California, Santa Barbara. Prior to joining UCSB in 2004, he was a Principal Scientist at the Xerox Palo Alto Research Center (PARC).

He received an Engineering Degree from the University of Gent in 1982, a Ph.D. in Electrical Engineering from Stanford University in 1986, and was a postdoctoral scientist at IBM Yorktown Heights (1986-1988) and a Senior Member of Research Staff at Philips Laboratories in Briarcliff Manor (1988-1991).

He has published over 350 research papers, holds 23 patents, has given 160 invited and plenary talks at international conferences, and was included in the 2014 “Highly Cited Researchers” list (www.highlycited.com). Van de Walle is a Member of the National Academy of Engineering, 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, the Medard W. Welch Award from the AVS, and the TMS John Bardeen Award.

His research interests include novel electronic materials, wide-band-gap semiconductors (III-V nitrides, II-VI compounds), transparent conductors, and complex oxides; loss mechanisms in light emitters; two-dimensional conductors; quantum information science; and physics and chemistry of hydrogen interactions with solids.