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Light-emitting diodes (LEDs) have become ubiquitous in modern life, powering a wide range of devices, from smartphones and laptops to home lighting solutions and automotive systems. However, the current generation of LEDs has a significant drawback – when we increase their power for added brightness, efficiency takes a significant hit, resulting in reduced performance and increased energy consumption.
A team of researchers at Nagoya University in Japan has introduced an innovative approach that promises to make LEDs brighter while maintaining their efficiency, thereby reducing the cost and environmental impact of LED production. Their groundbreaking research aims to improve performance in various applications, including visible light communication, virtual reality (VR) glasses, and micro-LED displays for mobile devices and large televisions.
“The innovation of this work lies in a better understanding of the effects of polarization, an intrinsic property of the gallium nitride/indium gallium nitride (GaN/InGaN) layer structure that is essential for light generation,” lead researcher Markus Pristovsek explained. “By optimizing the polarization of InGaN layers, we can create LEDs that are not only brighter but also more energy-efficient, paving the way for a new generation of LED technologies.”
Indium gallium nitride (InGaN) LEDs are widely considered the world’s most efficient source of light, although they generally function at low power levels. To achieve greater brightness, it is essential to raise their power, but this typically leads to a reduction in efficiency, a phenomenon referred to as efficiency droop. This efficiency droop has been a major challenge for LED manufacturers, limiting the performance and adoption of LED-based technologies.
To overcome this hurdle, expanding the LED area can result in more light output, but this also requires a larger chip, leading to fewer LEDs being produced from a single wafer – the thin, flat semiconductor base made of InGaN used to fabricate LED devices. This, in turn, results in higher manufacturing costs and a larger environmental footprint, making it essential to develop more efficient and sustainable LED production methods.
Researchers have been actively working on mitigating efficiency droop by tilting InGaN layers and adjusting the wafer orientations, which significantly alters the crystal properties. One crucial property affected by this technique is ‘polarization,’ which plays a critical role in determining the efficiency of LEDs. Although tilted orientations with low polarization have been under study for over 15 years, InGaN LEDs produced with these angles have consistently demonstrated less than 50% efficiency compared to standard high-polarization LEDs.
A study conducted by Pristovsek and Nan Hu at the Center for Integrated Research of Future Electronics (CIRFE) at Nagoya University revealed that lower polarization is advantageous only when it aligns with the orientation of standard LEDs. Building on this insight, the researchers grew LEDs on an economical sapphire substrate in the (10-13) orientation, which features reduced polarization while maintaining a direction akin to conventional LEDs. This innovative approach enables the creation of LEDs with improved efficiency at higher power levels, opening up new possibilities for LED-based technologies.
These (10-13) LEDs demonstrate improved efficiency at higher power levels, indicating new possibilities for manufacturers to create advanced LED technologies, such as more efficient and brighter micro-LED screens for mobile devices and large televisions. Increased current density capacity could also lead to novel applications in automotive and specialized industrial lighting, while quicker switching speeds could be useful in visible-light communication technology and VR eyewear.
“Future research is unlikely to find a better orientation, particularly on the cost-efficient sapphire substrates, because only two tilted directions can be fit to it,” Pristovsek said. “However, there are other ways to make (10-13) LEDs with fewer defects on sapphire and maybe even silicon. But the other orientations achieved on sapphire or silicon so far are worse because they are either inherently rough, they increase the amount of polarization, or they have the wrong sign of polarization.”
Journal reference:
- Markus Pristovsek, Nan Hu. How to Make Semi-Polar InGaN Light Emitting Diodes with High Internal Quantum Efficiency: The Importance of the Internal Field. Laser & Photonics Reviews, 2024; DOI: 10.1002/lpor.202400529
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