A Caltech Library Service

Ultrafast Hot Carrier Dynamics in GaN and its Impact on the Efficiency Droop

Jhalani, Vatsal A. and Zhou, Jin-Jian and Bernardi, Marco (2017) Ultrafast Hot Carrier Dynamics in GaN and its Impact on the Efficiency Droop. Nano Letters, 17 (8). pp. 5012-5019. ISSN 1530-6984. doi:10.1021/acs.nanolett.7b02212.

[img] PDF - Accepted Version
See Usage Policy.

[img] PDF - Submitted Version
See Usage Policy.

[img] PDF (Origin of the stronger average e-ph coupling strength for electrons compared to holes; (Figure S1) Phonon mode-resolved electron–phonon scattering rates; (Figure S2) Origin of the stronger average electron–phonon coupling strength for electrons...) - Supplemental Material
See Usage Policy.


Use this Persistent URL to link to this item:


GaN is a key material for lighting technology. Yet, the carrier transport and ultrafast dynamics that are central in GaN light-emitting devices are not completely understood. We present first-principles calculations of carrier dynamics in GaN, focusing on electron–phonon (e-ph) scattering and the cooling and nanoscale dynamics of hot carriers. We find that e-ph scattering is significantly faster for holes compared to electrons and that for hot carriers with an initial 0.5–1 eV excess energy, holes take a significantly shorter time (∼0.1 ps) to relax to the band edge compared to electrons, which take ∼1 ps. The asymmetry in the hot carrier dynamics is shown to originate from the valence band degeneracy, the heavier effective mass of holes compared to electrons, and the details of the coupling to different phonon modes in the valence and conduction bands. We show that the slow cooling of hot electrons and their long ballistic mean free paths (over 3 nm at room temperature) are a possible cause of efficiency droop in GaN light-emitting diodes. Taken together, our work sheds light on the ultrafast dynamics of hot carriers in GaN and the nanoscale origin of efficiency droop.

Item Type:Article
Related URLs:
URLURL TypeDescription Information Paper
Jhalani, Vatsal A.0000-0003-0866-0858
Zhou, Jin-Jian0000-0002-1182-9186
Bernardi, Marco0000-0001-7289-9666
Alternate Title:Asymmetry in the Hot Carrier Dynamics in GaN and its Impact on the Efficiency Droop
Additional Information:© 2017 American Chemical Society. Received: May 25, 2017; Revised: July 20, 2017; Published: July 24, 2017. V.J. thanks the Resnick Sustainibility Institute at Caltech for fellowship support. J.-J.Z. acknowledges support from the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, as follows: the development of the computational methods employed in this work was supported through the Office of Science of the U.S. Department of Energy under Award No. DE-SC0004993. M.B. acknowledges support by the National Science Foundation under Grant No. ACI-1642443, which provided for basic theory and part of the electronphonon coupling code development. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors thank Davide Sangalli for fruitful discussions. Author Contributions: M.B. conceived and designed the research. V.J. and J.-J.Z. developed the computational codes and carried out the calculations. All authors wrote the manuscript. The authors declare no competing financial interest.
Group:JCAP, Resnick Sustainability Institute
Funding AgencyGrant Number
Resnick Sustainability InstituteUNSPECIFIED
Department of Energy (DOE)DE-SC0004993
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:Gallium nitride, light emitting diodes, ultrafast dynamics, electron-phonon scattering
Issue or Number:8
Record Number:CaltechAUTHORS:20170705-124137567
Persistent URL:
Official Citation:Ultrafast Hot Carrier Dynamics in GaN and Its Impact on the Efficiency Droop. Vatsal A. Jhalani, Jin-Jian Zhou, and Marco Bernardi Nano Letters 2017 17 (8), 5012-5019. DOI: 10.1021/acs.nanolett.7b02212
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78766
Deposited By: Tony Diaz
Deposited On:05 Jul 2017 22:47
Last Modified:15 Nov 2021 17:42

Repository Staff Only: item control page