PIONNERING EXPERIMENT
MYSTERY of NITRIDE LEDs
HOW ELECTRON EMISSION UNCOVERED THE LAST MYSTERY OF NITRIDE LEDS
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Jean-Yves DUBOZ * Centre de Recherche sur l’ HétéroEpitaxie et ses Applications( CRHEA); Université Côte d ' Azur, Valbonne-Sophia-Antipolis, France * jyd @ crhea. cnrs. fr
The remarkable energy efficiency of GaN-based white LEDs has made them the cornerstone of modern lighting. Yet behind this global commercial triumph lay a lingering mystery: why do these LEDs lose efficiency at high currents? That question has finally been answered, thanks to a groundbreaking physics experiment based on electron emission.
https:// doi. org / 10.1051 / photon / 202613724
This is an Open Access article distributed under the terms of the Creative Commons Attribution License( https:// creativecommons. org / licenses / by / 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Historical context
Sometimes, technological breakthroughs with major societal impact emerge ahead of our fundamental scientific understanding. The rise of LED lighting is a striking example: high-performance LEDs reached the market even as key aspects of the physics behind GaN, the material at their core, remained poorly understood. In fact, the 2014 Nobel Prize in Physics was awarded to three materials scientists not only for their technical achievement but also for the profound societal impact of their work. While science initially struggled to explain how these imperfect materials could emit light so efficiently, it has now caught up, uncovering why those same LEDs lose efficiency at high currents. Among the key factors behind the success of nitride LEDs( GaN and its InGaN and AlGaN alloys) were major advances in material science, notably the improvement of GaN crystal quality through a two-step growth process on sapphire substrates, and above all, the achievement of p-type doping via the activation of magnesium acceptor dopant atoms. This activation, first discovered accidentally under electron irradiation and later optimized through thermal annealing, ultimately led to the Nobel Prize together with the discovery of the nucleation layer which leads to materials with high crystalline order. However, the level of p-type doping remained limited compared to n-type doping which might lead to holes injected from the p-side( 7 in Fig. 1) being fewer than electrons injected from the n-side( 1 in Fig. 1). This imbalance might occur in the central region of the LED, composed of InGaN quantum wells, where electron – hole recombination takes place to generate light( 2 in Fig. 1). The non-recombining excess electrons
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