Image: Point defects in light-emitting diodes can reduce the efficiency of the device. Computational calculations can elucidate the defects and mechanisms responsible and make lighting less energy intensive

 

Semiconductor devices such as light-emitting diodes (LED), solar cells, and transistors are the building blocks of modern technologies, and therefore are at the front lines of the effort to reduce energy consumption and produce energy in more sustainable ways. In order to elucidate the mechanisms of efficiency loss, we use first-principles calculations to study a variety of properties of III-nitride materials, which are key to LED and transistor technologies.

We have developed methodologies to determine surface energies of polar crystal facets, which are important quantities for understanding growth, as well as the rate of radiative and nonradiative processes at point defects, which limit the efficiency of LED devices. We are particularly interested in the treatment and effect of electronic excited states of defects.

Online talks:

Also, a short talk I gave on light-emitting diodes and a seminar on Shockley-Read-Hall recombination.

Related publications:

Jimmy-Xuan Shen, Darshana Wickramaratne, Cyrus E. Dreyer, Audrius Alkauskas, Erin Young, James S. Speck, and Chris G. Van de Walle,
Calcium as a nonradiative recombination center in InGaN,
Appl. Phys. Express, 10, 021001 (2017)

Darshana Wickramaratne, Jimmy-Xuan Shen, Cyrus E. Dreyer, Manuel Engel, Martijn Marsman, Georg Kresse, Saulius Marcinkevicius, Audrius Alkauskas, and Chris G. Van de Walle,
Iron as a source of efficient Shockley-Read-Hall recombination in GaN,
Applied Physics Letters 109, 162107 (2016)

Audrius Alkauskas, Cyrus E. Dreyer, John L. Lyons, and Chris G. Van de Walle,
Role of excited states in Shockley-Read-Hall recombination in wide-band-gap semiconductors,
Physical Review B 93, 201304(R) (2016), Editor’s Suggestion, arXiv:1605.05673

Cyrus E. Dreyer, Audrius Alkauskas, John L. Lyons, James S. Speck, and Chris G. Van de Walle,
Gallium vacancy complexes as a cause of Shockley-Read-Hall recombination in III-nitride light emitters,
Applied Physics Letters 108, 141101 (2016), Selected for feature article and issue cover

Cyrus E. Dreyer, Anderson Janotti, and Chris G. Van de Walle,
Absolute surface energies of polar and nonpolar planes of wurtzite GaN,
Phys. Rev. B 89, 081305(R) (2014) Editor’s Suggestion

Collaborators:

Chris G. Van de Walle, University of California, Santa Barbara

Audrius Alkauskas, Center for Physical Sciences and Technology, Vilnius, Lithuania

John L. Lyons, United States Naval Research Lab

Darshana Wickramaratne, United States Naval Research Lab

Anderson Janotti, University of Delaware

Press coverage:

LED Lighting May Now Shine Brighter: Scientists apprehended the atomic-scale, microscopic mechanism that limits light emission in LED lighting
News Wise, March 1, 2017

LEDs: Resolving the iron conundrum
Compound Semiconductor, December 2016

Trace amounts of transition-metal impurities in GaN kill LED efficiency
Semiconductor Today, November 11, 2016

Trace metal recombination centres kill LED efficiency
Compound Semiconductor, November 7, 2016

Trace metal recombination centers kill LED efficiency
AAAS Eureka Alert, November 3, 2016

Supercomputers Help Identify Efficiency-Limiting Defects in LEDs
NERSC.gov, July 18, 2016

LED lighting may now shine brighter
US DOE Office of Science, Science Highlight, July 1, 2016

Unravelling the nature of point defects in nitride LEDs
Compound Semiconductor, June 4, 2016

Defects in LED diodes that lead to less efficient solid state lighting identified
Energy Daily, April 13, 2016

Certain type of vacancy in gallium nitride based LEDs lowers their efficiency
Laser Focus World, April 11, 2016

Identifying defects in LED materials promises more efficient lighting
Smart2Zero, April 7, 2016

UCSB researchers identify specific defects in LED diodes that lead to less efficient solid state lighting
AAAS Eureka Alert, April 6, 2016

Researchers identify specific defects in LED diodes that lead to less efficient solid state lighting
Phys.org, April 6, 2016

Becoming Crystal Clear: UCSB researchers identify specific defects in LED diodes that lead to less efficient solid state lighting
The UC Santa Barbara Current, April 5, 2016

Theoretical technique identifies defects in LED materials
Photonics Media, April, 2016

Aiding nitride growth with accurate surface energies
Compound Semiconductor, May 19, 2014