In the 1980s, all known material systems possessing the necessary properties for blue‐light emission had shortcomings, thus negating their utilization in efficient LEDs. Gallium nitride (GaN) was one ...possible candidate, though, at the time, no p‐type or active layer could be created. These challenges were ultimately overcome by Shuji Nakamura, who describes the path to the first blue GaN LED in his Nobel Lecture.
Shuji Nakamura discovered p‐type doping in Gallium Nitride (GaN) and developed blue, green, and white InGaN based light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made ...possible energy efficient, solid‐state lighting systems and enabled the next generation of optical storage. Together with Isamu Akasaki and Hiroshi Amano, he is one of the three recipients of the 2014 Nobel Prize in Physics. In his Nobel lecture, Shuji Nakamura gives an overview of this research and the story of his inventions***.
Shuji Nakamura discovered p‐type doping in Gallium Nitride (GaN) and developed blue, green, and white light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made possible energy efficient, solid‐state lighting systems and enabled the next generation of optical storage. Together with Isamu Akasaki and Hiroshi Amano, he is one of the three recipients of the 2014 Nobel Prize for Physics. In his Nobel lecture, Shuji Nakamura gives an overview of this research and the story of his inventions.
The history of development for gallium-nitride-based light-emitting diodes (LEDs) is reviewed. We identify two broad developments in GaN-based LED technology: first, the key breakthroughs that ...enabled the development of GaN-based devices on foreign substrates like sapphire (first-generation LEDs), and, second, a new wave of devices benefiting from developments in GaN substrate manufacturing, which has led to native bulk-GaN-based LEDs with unprecedented performance characteristics that portend a disruptive shift in LED output power density and the corresponding cost of generating light.
The realization of the first high-brightness blue-light-emitting diodes (LEDs) in 1993 sparked a more than twenty-year period of intensive research to improve their efficiency. Solutions to critical ...challenges related to material quality, light extraction, and internal quantum efficiency have now enabled highly efficient blue LEDs that are used to generate white light in solid-state lighting systems that surpass the efficiency of conventional incandescent lighting by 15–20×. Here we discuss the initial invention of blue LEDs, historical developments that led to their current state-of-the-art performance, and potential future directions for blue LEDs and solid-state lighting.
La mise au point des premières diodes électroluminescentes (LED) bleues en 1993 a marqué le début de plus de vingt années de recherches intensives dans le but d'améliorer leur efficacité. Les solutions qui ont été apportées à des défis critiques associés à la qualité des matériaux, à l'extraction de la lumière et au rendement quantique interne permettent à présent de disposer de LED bleues hautement performantes utilisables pour générer de la lumière blanche dans des systèmes d'éclairage à l'état solide qui surpassent en efficacité les ampoules à incandescence d'un facteur de 15 à 20×. Nous évoquons ici les prémices de l'invention des LED à lumière bleue, l'histoire des développements qui ont mené à la performance de l'état de l'art actuel, ainsi que de potentielles futures directions de recherche en matière de LED à lumière bleue et d'éclairage à l'état solide.
The developments of high performance InGaN based micro-light-emitting diodes (μLEDs) are discussed. We first review the early demonstrations of μLEDs and the state-of-the-art outstanding achievements ...on the emerging high-quality display and visible-light communication applications. Due to the miniature dimensions of μLEDs, the key understandings and the significant device advancements to achieve excellent energy efficiency are addressed. Lastly, two other critical challenges of μLEDs, namely full-color scheme and mass transfer technique, and their potential solutions are explored for future investigations.
Ultrasmall blue InGaN micro-light-emitting diodes (µLEDs) with areas from 10−4 to 0.01 mm2 were fabricated to study their optical and electrical properties. The peak external quantum efficiencies ...(EQEs) of the smallest and largest µLEDs were 40.2 and 48.6%, respectively. The difference in EQE was from nonradiative recombination originating from etching damage. This decrease is less severe than that in red AlInGaP LEDs. The efficiency droop at 900 A/cm2 of the smallest µLED was 45.7%, compared with 56.0% for the largest, and was lower because of improved current spreading. These results show that ultrasmall µLEDs may be fabricated without a significant loss in optical or electrical performance.
High-efficiency light-emitting diodes emitting amber, green, blue, and ultraviolet light have been obtained through the use of an InGaN active layer instead of a GaN active layer. The localized ...energy states caused by in composition fluctuation in the InGaN active layer are related to the high efficiency of the InGaN-based emitting devices. The blue and green InGaN quantum-well structure light-emitting diodes with luminous efficiencies of 5 and 30 lumens per watt, respectively, can be made despite the large number of threading dislocations (1 × 10$^8$ to 1 ×x 10$^{12}$ cm$^{-2}$). Epitaxially laterally overgrown GaN on sapphire reduces the number of threading dislocations originating from the interface of the GaN epilayer with the sapphire substrate. InGaN multi-quantum-well structure laser diodes formed on the GaN layer above the SiO$_2$ mask area can have a lifetime of more than 10,000 hours. Dislocations increase the threshold current density of the laser diodes.
Optoelectronic effects of sidewall passivation on micro-sized light-emitting diodes (µLEDs) using atomic-layer deposition (ALD) were investigated. Moreover, significant enhancements of the optical ...and electrical effects by using ALD were compared with conventional sidewall passivation method, namely plasma-enhanced chemical vapor deposition (PECVD). ALD yielded uniform light emission and the lowest amount of leakage current for all µLED sizes. The importance of sidewall passivation was also demonstrated by comparing leakage current and external quantum efficiency (EQE). The peak EQEs of 20 × 20 µm
µLEDs with ALD sidewall passivation and without sidewall passivation were 33% and 24%, respectively. The results from ALD sidewall passivation revealed that the size-dependent influences on peak EQE can be minimized by proper sidewall treatment.
The efficiency droop of light emitting diodes (LEDs) with increasing current density limits the amount of light emitted per wafer area. Since low current densities are required for high efficiency ...operation, many LED die are needed for high power white light illumination systems. In contrast, the carrier density of laser diodes (LDs) clamps at threshold, so the efficiency of LDs does not droop above threshold and high efficiencies can be achieved at very high current densities. The use of a high power blue GaN-based LD coupled with a single crystal Ce-doped yttrium aluminum garnet (YAG:Ce) sample was investigated for white light illumination applications. Under CW operation, a single phosphor-converted LD (pc-LD) die produced a peak luminous efficacy of 86.7 lm/W at 1.4 A and 4.24 V and a peak luminous flux of 1100 lm at 3.0 A and 4.85 V with a luminous efficacy of 75.6 lm/W. Simulations of a pc-LD confirm that the single crystal YAG:Ce sample did not experience thermal quenching at peak LD operating efficiency. These results show that a single pc-LD die is capable of emitting enough luminous flux for use in a high power white light illumination system.
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