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Colloquium: September 16, 2015

Ümit Özgür*
III-Nitride LEDs for Lighting: Opportunities and challenges
Day Time Place
September 16, 2015 Wednesday 15:40 EE01

Host: A. Aydinli

ABSTRACT — Light Emitting Diodes (LEDs) have become indispensable in a variety of applications from displays to general lighting, offering energy savings, environmental protection and safety, and long operation lifetimes. At the center of this blazing journey is the GaN based LED, which still has its mysteries in that its efficiency degrades with increasing drive current aside from thermal issues, more severely for the green emitting variety. Significant research efforts have been put forth for understanding this efficiency degradation, which is clearly caused by a nonradiative loss mechanism that can be effective inside and outside the quantum wells of the LED active region. Possible remedies have been explored to combat the potential culprits such as Auger recombination augmented by strong nonuniformity of carrier distributions and carrier overflow due to ballistic and quasi-ballistic transport. Upon optimization of growth and device design schemes, internal quantum efficiencies in the 90% range have already become accessible and power conversion efficiencies for white light generation using blue LEDs have reached over 65%. While attainment of packaging with efficient heat removal and cutting cost are currently the key focus areas, unequivocal design rules are yet to be established to overcome efficiency degradation. This talk will include an overview of the status of lighting by LEDs and a discussion of nitride LED device physics with emphasis on efficiency limiting mechanisms as well as potential remedies for the efficiency degradation. Challenging problems from both materials growth and device design fronts will be elaborated on..

*Virginia Commonwealth University, Richmond, VA USA

The Physics Colloquia are designed to address a non-specialist, broad audience and introduce topics of contemporary research through lectures by leading experts. We warmly invite all members of the student body, including undergraduates enrolled in any programme.

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