OSE Seminar with Alumni, Dr. Arman Rashidi on Carrier dynamics in III-nitride light-emitting diodes: An RF approach to understand efficiency issues

Departmental News

Dr. Arman Rashidi

Posted: February 16, 2019

Date: Thursday, February 21, 2019 

Time:  11:00 AM to Noon

Location:  CHTM, Room 101

Map to CHTM:


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Dr. Arman Rashidi
Research Scientist


III-nitride light-emitting diodes (LEDs) are now ubiquitous in solid-state lighting (SSL) systems. Despite the significant advancement of III-nitride LEDs, the origins of fundamental challenges such as efficiency droop, thermal droop, and green gap are not completely understood. In addition, emerging applications such as micro-pixel LED displays and visible-light communication (VLC) require efficient LEDs capable of high-speed modulation. Studies of carrier dynamics are essential to better understand the fundamental efficiency challenges and enable the design of high-efficiency, high-speed LEDs. Among approaches to characterize the carrier dynamics in LEDs, electrically injected methods are preferred over optically pumped methods to capture the carrier dynamics under typical operating conditions. In this talk, a comprehensive method is developed to study carrier dynamics in electrically injected LEDs using small-signal RF measurements and differential rate equation analysis. This method represents an entirely new approach to characterizing the classic DC properties of III-nitride LEDs and enables the simultaneous determination of the dynamic properties. This method enabled the determination of the injection efficiency, carrier density in the active region, modulation bandwidth and differential carrier lifetime, carrier escape lifetime, radiative and non-radiative recombination rates, and RC time constant in LEDs. Understanding the above properties under electrical injection provides valuable information about the origins of fundamental efficiency challenges and aids in the co-optimization of modulation bandwidth and efficiency. This approach is expected to accelerate the development of LEDs tailored for micro-pixel displays and VLC.


Arman Rashidi is a postdoctoral fellow at the Center for High Technology Materials (CHTM), working with Prof. Feezell’s group.  He earned his Ph.D. in Optical Science and Engineering in 2018 under the guidance of Prof. Feezell at UNM. Prior to coming to UNM, he earned a B.S. and an M.S. degree from Shiraz University, Iran, in 2012 and 2014, respectively. His current research includes a study of efficiency issues in GaN-based LEDs and lasers.