D. Feezell1,*, X. Li1, E. DeJong1, N. Pant2, A. Elshafiey1, S. Rahman3, A. Armstrong4, S. Rajan3, E. Kioupakis2, and R. Armitage5

*email: dfeezell@unm.edu

 

The carrier dynamics in InGaN/GaN light-emitting diodes (LEDs) are directly tied to their efficiency and maximum modulation speed, which are important metrics for solid-state lighting, displays, and optical communication. In this work, we measure the carrier dynamics of a variety of commercial-grade c-plane InGaN/GaN LEDs using small-signal electroluminescence (SSEL) methods [1]. A rate equation approach and associated small-signal circuit are used to model carrier injection, recombination in the active region, recombination in the cladding regions, and carrier escape. The model is fit to the measured optical frequency response (S21) and input impedance (S11) of the LEDs to extract the various carrier lifetimes, the carrier density, and the recombination rates. We first present measurements on a wavelength series consisting of LEDs with the same active region design but different indium compositions. The results offer insights into the contributions of the quantum confined Stark effect (QCSE) and InGaN material quality on the green gap [2]. Next, we present measurements on a defect-density series consisting of LEDs with the same active region design and indium composition, but with different point defect densities. We then study the impact of deep-level defect density on trap-assisted Auger–Meitner recombination (TAAR) and show that TAAR accounts for a relatively small fraction of the total nonradiative recombination, which is dominated by intrinsic Auger–Meitner recombination in the samples studied [3]. SSEL results offer insights into the underlying causes of efficiency droop and the green gap and may inform application specific design strategies for higher efficiency LEDs.

[1] A. Rashidi, et. al., “Differential carrier lifetime and transport effects in electrically injected III-nitride light-emitting diodes,” Journal of Applied Physics, 122(3), 035706 (2017).

[2] X. Li, et al., “Carrier dynamics in blue, cyan, and green InGaN/GaN LEDs measured by small-signal electroluminescence,” Applied Physics Letters, 122(21), 212108 (2023).

[3] X. Li, et al., “Influence of trap-assisted and intrinsic Auger–Meitner recombination on efficiency droop in green InGaN/GaN LEDs,” Applied Physics Letters, 123(11), 112109 (2023).

 

Daniel Feezell is a Professor, Regents’ Lecturer, and Director of Graduate Programs in the ECE Department and a member of the Center for High Technology Materials at UNM. He received the Ph.D. degree in 2005 from the University of California Santa Barbara (UCSB). Prior to joining UNM, he was a Project Scientist in the Solid-State Lighting and Energy Center at UCSB and worked for Soraa, a GaN-based LED and laser start-up company. His research includes epitaxial growth and fabrication of group-III nitrides, high-efficiency and high-speed LEDs; nanoscale selective-area epitaxy, vertical-cavity surface-emitting lasers, and wide-bandgap power electronics. He has authored or co-authored over 150 journal and conference publications and holds more than 20 U.S. patents. Dr. Feezell received an NSF CAREER award in 2015 and a DARPA Young Faculty Award in 2013.  Dr. Feezell’s projects have been funded by DOE, DOD, DARPA, ARPA-E, NSF, DTRA, and the commercial sector.  He is a Senior Member of IEEE.