Researchers pin-point carrier localization states in InGaN LEDs

September 05, 2019 //By Julien Happich
InGaN LEDs
A team of researchers at the Hong Kong University of Science and Technology have reported what they believe to be the first direct observation of transition carriers between different localization states within a InGaN LED structure.

Localization states theory is commonly used to explain the high luminescence efficiency gained via the large number of dislocations within the materials of InGaN LEDs. Localization states are the energy minima states believed to exist within the InGaN quantum well region (discrete energy values), but a direct observation of localization states was elusive until now.

The researchers confirmed their observation of localization states by temperature-dependent photoluminescence and excitation power-dependent photoluminescence, which they reported in the Journal of Applied Physics under the title “Visualizing carrier transitions between localization states in a InGaN yellow–green light-emitting-diode structure”.

"Based primarily on indium content fluctuations, we explored the 'energy minima' that remain within the InGaN quantum well region," said Yangfeng Li, the paper's lead author and a now postdoctoral fellow at the Hong Kong University of Science and Technology.


The transition process of carriers between different localization
states with increasing temperatures. Credit: Yangfeng Li.

"Such energy minima will capture the charge carriers—electrons and holes—and prevent them from being captured by defects (dislocations). This means that the emission efficiency is less affected by the large number of defects."

Based on the group's electroluminescence spectra, "the InGaN sample with stronger localization states provides more than a twofold enhancement of the light-output at the same current-injection conditions as samples of weaker localization states," Li observed. The researchers' work can serve as a reference about the emission properties of InGaN materials for use in manufacturing LEDs and laser diodes.

Hong Kong University of Science and Technology - www.ust.hk


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