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Full color micro-displays with a pixel pitch of below 10 µm are needed for augmented and virtual reality applications. In the native emission approach, high efficiency Red-Green-Blue (RGB) pixels could be achieved using monolithically integrated InGaN based micro-LEDs. We have demonstrated the growth of monolithic RGB InGaN nanopyramids of diameter less than 1 µm by metal organic vapor phase epitaxy (MOVPE). The nanopyramids are obtained by nanoselective area growth using an in situ patterned epitaxial graphene on SiC as an embedded mask. Particularly, the red emitting InGaN/InGaN quantum wells are regular while their In content is very high, up to 40%. Nanoscale optical and structural properties of these RGB nanopyramids will be presented.

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The AR and smart glasses market is expanding with “AI glasses” that do not have displays for AR but have a casual design and multi-modal AI features, which would significantly enhance the consumer experience. On the other hand, this trend also affects AR glasses, and “AI-AR glasses” is expected to be the future trend. Combining free-form or birdbath optical methods with Micro OLED has established its position in the AR industry. Still, devices need further miniaturization, and the future trend will be to integrate advanced display technologies such as Micro LED or Micro OLED with waveguide methods. However, improving optical efficiency and image reproducibility continues to be a challenge, and several companies in the Japanese industry are addressing these issues. With the latest market trends in global AR and smart glasses, this presentation will also highlight Japanese companies that are becoming more active in optical industries and unravel the international expansion strategies of Japanese companies.

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We present a bottom-up technology for producing dislocation-free, strain-relaxed InGaN microLEDs in the form of sub-micron scale hexagonal platelets. The use of InGaN barrier material enables high Indium-contents quantum wells with emission tunable from blue to deep red (>670nm). These platelets do not suffer from plasma induced damage and exhibit internal quantum efficiency values up to 60% for deep red emitting quantum wells. We further show red microLEDs exhibiting dominant wavelengths above 630nm for drive currents up to 50A/cm2, which is well suited for wide color gamut, and ultra-high brightness displays.

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Nanowire-based LEDs have the unique ability to maintain high efficiencies as the LED size becomes quite small, contrary to conventional thin-film LEDs. More recently, reports have shown nanowire LEDs in the green with >25% external quantum efficiency (EQE) and red with >8% EQE, competitive with the best direct green and InGaN red LEDs ever fabricated – despite being sub-micron in size. These structures were obtained by molecular beam epitaxy (MBE) using a selective area epitaxy (SAE) technique, where nanostructures can be controllably grown on thin-film templates. This work presents a pathway towards the wafer-scale production of nanowire LEDs for displays, focusing on new processes that are already in production at the wafer-scale.

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Micron or even submicron GaN micro-LEDs are highly required from AR microdisplays. However, fabrication of high-efficiency submicron GaN micro-LEDs remains a significant technical challenge due to the existence of strong sidewall nonradiative recombination induced by ICP etching. We employed an ultralow damage dry etching technique, i.e., neutral beam etching, to fabricate GaN micro-LEDs. In this technique, charged ions are transformed into a beam of neutral particles when ions passed through apertures opened in a carbon plate placed between plasma discharge and etching chamber, thus enabling ultralow damage etching of various materials. We have demonstrated 3.5 3.5 m 2 GaN blue micro-LEDs with negligible sidewall nonradiative recombination by using the neutral beam etching technique [1]. We further extended this technique to the fabrication of submicron GaN micro-LEDs. In this talk, I will present recent progresses on the fabrication of submicron GaN micro-LEDs, including the demonstration of a GaN micro-LED with a diameter as small as 200 nm. [1] X. L. Wang, et al., Nat. Commun. 14 (2023) 7569.

The GaN material system offers a wide range of applications, including light emitters covering a broad spectral range from visible to ultraviolet light, as well as high-power and radio-frequency transistors. A crucial material property of III-nitrides utilized in heterostructure design is the built-in polarization. Since GaN primarily crystallizes in the wurtzite structure, which breaks inversion symmetry along the c-axis [0001], opposite surfaces along this direction exhibit drastically different physical and electronic properties. This fact can be leveraged for specific applications. However, since polarization is dictated by the substrate polarity, until now, the use of a single wafer implied only one alignment of polarization in the devices grown on top of it.

In this work, we propose leveraging the unique advantages of the GaN material system, its wide range of applications, and the support of high-quality bulk substrates to develop a new method for monolithic integration of electronic and optoelectronic devices on the same wafer. By utilizing consecutive epitaxial growth processes on both polarities of GaN substrates, i.e., the gallium face (0001) and nitrogen face (000-1), it is possible to achieve structures with distinct physical and chemical properties on the same bulk crystal. We demonstrate the ability to control epitaxial growth on both polarities of GaN by plasma-assisted molecular beam epitaxy, presenting the monolithic integration of a metal-polar light-emitting diode (LED) and a nitrogen-polar high electron mobility transistor (HEMT) [1], as well as double-sided LEDs emitting at distinct wavelengths. The obtained integrated structures can pave the way for new device functionalities.
[1] L. van Deurzen, E. Kim, et al., Nature, 634 (2024) 334.

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The miniaturization of LEDs has enabled their application in displays of various sizes, with Micro-LEDs emerging as a transformative technology in the field of micro-displays. Known for their high brightness, low power consumption, and exceptional reliability, Micro-LEDs are widely regarded as the optimal solution for AR/XR terminal devices. Early development of Micro-LED micro-displays built upon traditional LED manufacturing processes, utilizing sapphire and flip-chip solutions for low-resolution displays. However, these approaches faced significant limitations in meeting the stringent requirements of AR/XR applications, particularly due to challenges in GaN material growth and integration processes, which hindered the realization of single-chip full-color displays. Recent advancements in single-chip integration technology have paved the way for wafer-level full-color Micro-LED micro-display chips, positioning this technology as a leading candidate for future AR/XR systems.

A notable breakthrough in this field is the development of a 0.13-inch micro-display with a full-color resolution of 320×240 (Micro-LED resolution of 640×480) and color performance exceeding 100% of the DCI-P3 standard. This technology achieves a peak full-color brightness of 500,000 nits while maintaining low power consumption, with a single-chip full-color light engine volume of just 0.18cc, the smallest in its class. The architecture also demonstrates significant potential for further performance enhancements. Beyond display capabilities, this innovation represents a critical step toward mass production, leveraging quantum dot lithography as a highly feasible approach for full-color Micro-LED micro-display fabrication. The integration of versatile interfaces, such as MIPI and QSPI, ensures broad compatibility with diverse hardware systems, reducing development costs and accelerating adoption in AR/XR applications. These advancements underscore the potential of Micro-LED technology to redefine micro-displays for next-generation AR/XR devices.

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The development of Micro LED display technology targets four major applications. The most urgent task for large-sized displays is to accelerate scaling through the optimization of design and technology. Specific approaches include reducing chip size, flexibly utilizing various mass transfer technologies, improving testing solutions, and addressing edge wiring and seamless splicing issues through more diverse methods. To achieve breakthroughs in wearable devices and automotive display applications, the core
focus should be on leveraging the unique advantages of Micro LED technology. This involves the integration of display and sensing components, as well as the development and mass production of transparent displays. Silicon-based products offer new avenues for the integration and application of Micro LED technology. The industry is currently focused on overcoming challenges such as optimizing manufacturing processes, developing bonding solutions, achieving full-colorization, and more.

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