We discuss state of the art microLED performance for AR and direct view display applications, including a detailed comparison of both InGaN and AlInGaP material systems at various sizes from <2micron to >10micron pixels. In particular, we detail our most recent results on efficiency, gamut coverage, and reliability. We also quantify how sidewall passivation can lead to high IQE for 2 micron scale devices. Further we describe early results for a polychromatic LED demonstration that represents a possible breakthrough display technology.

µLED devices are being designed for more and more applications due to a long list of promised display improvements including improved resolution, higher brightness, improved energy efficiency, high contrast ratio and more. Some technologies can employ direct emitters, which would have several advantages, however, there are certain circumstances where downconverted µLED solutions are beneficial. The advantages of color conversion from direct blue emission to green and red light become more pronounced as the dimensions of µLEDs continues to diminish to 10 µm and below. In particular, at these small length scales, few options for downconverters exist. However, colloidal Quantum Dots (QDs) are prime candidates for this task due to their small size and strong absorption properties. We outline the absorption, emission, and stability requirements for quantum dot materials placed in on-chip downconverter µLED systems.

As today’s world is unthinkable without light emitting devices, questions of throughput, yield and tight control of the ever-increasing specifications become an increasingly important topic in semiconductor device production. Especially the first steps in the value chain – epitaxy and plasma etching – are both complex and crucial for the quality and yield of the final devices. In this presentation, we will discuss the capabilities of optical in-situ metrology for both the epitaxial and the plasma etch process. We will demonstrate that the precision of the in-situ control can be substantially increased when the metrology is connected across the different processes and measurement results are used to analyse downstream processes. Also for post-epitaxial 2D wafer mapping, that is used for characterizing wafer uniformity, the analysis capabilities are strongly extended, when layer thickness information of the whole layer stack are available from the in-situ metrology of the previous growth. In the talk we will show examples from different opto-electronical devices and highlight new developments in metrology.

MOCVD technology has widely grown compound semiconductors for various applications, like Power/RF GaN and micro-LEDs. Precise control of wafer uniformity, defect density, and run-to-run consistency is essential for optimal results and reducing COO. High-speed rotation vertical reactors, with uniform deposition capabilities, enable a wide process window. Implementing these in a single wafer configuration enhances film uniformity through concentric temperature and flow patterns. The Propel® MOCVD 300mm single wafer reactor made 300mm semiconductor fabrication accessible to the nitride material system, critical for RF and micro-LEDs. This presentation covers latest Propel® 300mm MOCVD single wafer reactor advancements, including uniformity, repeatability, crystal quality for GaN/Si, GaN HEMT structure characterization, and GaN on Si LED wavelength uniformity. We'll discuss recent progress in red InGaN LED performance on 6” sapphire and 8” Si wafers, highlighting how Propel® MOCVD enhances high indium composition materials with Turbodisc® single wafer reactor technology.

We found that the GaInN nanopyramids, which are obtained by the similar growth method as the nanowires, provides a high In incorporation in the growth of GaInN/GaN MQS. When we grew the GaInN pyramids with an InN molar fraction of 21 %, the MQS overgrown on the nanopyramid exhibited the cathodoluminescence (CL) peak wavelength of 620 nm, which is approximately 80 nm longer than that of the MQS simultaneously grown on the GaN nanopyramids. The CL intensity at 620 nm in the MQS/GaInN nanopyramid structure is almost the same as that at 540 nm in the MQS/GaN nanopyramid structure.

This presentation will provide an overview of the state-of-the-art in the development of AlGaN-based far-UVC-LED technologies. We will explore origins for the observed decline in the external quantum efficiency (EQE) with decreasing emission wavelength and present different approaches to improve the RRE, CIE, and LEE of UV light emitters. We will also discuss design aspects for far-UVC irradiation systems and provide an outlook of future prospects of far-UVC-LED device technology as well as the potential for a wider use of far-UVC sources in applications like room air disinfection.

Narrow-band line-emitter phosphors offer improved lm/W for white LEDs, while maintaining high CRI. Especially Eu3+-doped phosphors are ideal from an emitter perspective. However, using Eu3+ for practical LEDs is hampered by the lack of absorption in the blue spectral region. To solve this problem, we have developed nano-engineered phosphors harvesting interparticle energy transfer (IFRET), an innovative approach to sensitize Eu3+, and other ions, in the blue spectral range. In this presentation, we will share our progress on our IFRET materials, as well as demonstrate high-quality (high QY and small-size) nano-YAG phosphors.

Phosphors with high color-conversion efficiency are crucial for high-performance full-color displays. Recent research by the authors achieved 7-fold enhancement in color-conversion efficiency through structurally engineered phosphors, where phosphor materials were integrated into a nano-photonic structure, specifically photonic crystal (PhC) to exploit resonant absorption. However, challenges remain, including the waste of excitation photons and complex nanofabrication. In this presentation, structural phosphor based on a resonant cavity (RC) is introduced. A thin 40-nm CQD film embedded in a tailored RC results in high absorption (~87%) and enhanced fluorescence (~29×), while the simple planar geometry obviates the need for complex nanofabrications.

Degradation mechanisms of 275-nm-band AlGaN quantum well deep-ultraviolet light-emitting diodes fabricated on a (0001) sapphire substrate were investigated under hard operation conditions. The optical output power (Po) initially decreased by about 20 % within the operating time less than 102 h and then gradually decreased to about 60 % by 484 h. Because the degradation of the wells was less significant than the Po reduction, the initial degradation is attributed essentially to the decrease in carrier injection efficiency, most likely due to de-passivation of initially H-passivated preexisting nonradiative recombination centers (NRCs) in a Mg-doped p-type Al0.85Ga0.15N electron blocking layer. According to our database on the species of vacancy-type defects acting as NRCs in GaN and AlN, vacancy clusters comprised of a cation vacancy and nitrogen vacancies are the most suspicious origins of the NRCs.

Two-dimensional (2D) materials represent an ultrathin material class with unique properties. For example, graphene as the first 2D material reported combines high electrical conductivity and high transparency making it ideally suited as transparent contact layer in GaN-based LEDs. Graphene has been grown by plasma-enhanced CVD and integrated into GaN-based light emitting devices for the visible and for the UV spectral range by a transfer-free approach. Pronounced lateral current spreading, and a reduced turn-on voltage indicate the suitability of our concept.

III-N UV LEDs are currently of major interest for applications such as sterilisation (UVC) and phototherapy (UVB). Most work to date has focussed on the AlGaN system which is relatively well understood, but this limits the possibility for bandgap engineering in the active region structure. In this presentation we will outline the demonstration of a UV Light emitting diode operating around 340 nm using boron containing (BAlGaN) quantum wells. The device exhibited a higher output intensity compare to the boron free reference sample prepared at the same time. The potential for using such alloys for UVB and UVC devices will be discussed.

GaN based microLED technology is particularly interesting for micro-displays for augmented reality. Beyond that, however, many additional applications exploiting the massively parallel nature of optical channels from microLED arrays are of interest. This includes microLED arrays for chip-based lensless microscopy, optogenetics, low power gas sensing, optical neuromorphic computing, high-speed maskless lithography or massively parallel line-of-sight communication in HPC centers (LIFI), replacing optical fibers. In order to drive large numbers of pixels at high frequencies in customized microLED arrays, the integration with a CMOS backplane chip is required. The talk will mostly focus on chip processing and hybrid integration techniques for microLEDs and the opportunities for GaN based photonic integration in general, and GaN/CMOS integration in particular. First applications of specially designed microLED arrays in the field of optical neuromorphic computing will also be discussed. Test results include pattern recognition of hand-written digits from the MNIST dataset.

InGaN/GaN µLEDs are a promising candidate to visible optical communication applications thanks to their high luminosity and high bandwidth. High data rate are reachable by using them as an array to realize parallel communication. To optimize their integration, we propose a CMOS compatible process to make the µLEDs directly on top of an ASIC and to use them as emitter and fast photodetector. We have demonstrated functional µLEDs on a 200mm silicon substrate and frequency characterization were performed for both emission and reception.

Micro-LEDs have demonstrated attractive applications including potentially next-generation display and 6G optical communication, due to their special characteristics of small size, localized light emission, and high heat dissipation ability. But challenges still exist in achieving full-color micro-LED display and high-speed optical communication. Recently, we have successfully realized novel full-color micro-LED display based on a single-chip utilizing multi-wavelength multi-quantum wells (MQWs), and stacked blue and yellow micro-LED arrays. High-bandwidth GaN-based micro-LED arrays of ~2GHz were also developed for applications in visible light communication of ~10Gbps.

Fraunhofer HHI’s hybrid photonic integration technology based on SiN and polymer waveguiding platforms enables photonic integrated circuits operating at wavelengths from the infrared down to the visible. Hybrid photonic integration processes allow integrating active photonic building blocks such as lasers and active sections, as well as non-reciprocal and non-linear functionalities. Those features prove the large potential of Fraunhofer HHI’s hybrid photonic integration technology in application domains such as sensing and quantum technologies.

We present an optical spectroscopic study of InGaAs/AlInAs active region of quantum cascade lasers grown by low pressure metal organic vapor phase epitaxy combined with subwavelength gratings fabricated by reactive ion etching. Fourier-transformed photoluminescence measurements were used to compare the emission properties of structures before and after processing the gratings. Our results demonstrate a significant increase of the photoluminescence intensity related to intersubband transitions in the mid-infrared, which is attributed to coupling with the grating modes via so called photonic Fano resonances. Our findings demonstrate a promising method for enhancing the emission in optoelectronic devices operating in a broad range of application-relevant infrared.

The solid state lighting revolution has brought tremendous benefits of greater light source efficiency, longevity and new applications. While most major lighting applications have seen over 50% replacement of conventional light sources, there is tremendous opportunity in new ideas for better spectral engineering, and where, when and how we use light. Digital lighting is the next wave in light source technology where close coupling of LEDs with electronics and optics enables energy-efficient and versatile lighting solutions across different sectors. Automotive lighting is being enhanced with adaptive lighting systems, improving safety. Mobile phones now boast adaptive flash for better imaging. General Illumination has the potential for a significant shift towards smart and connected systems, optimizing energy usage by delivering the light dynamically, thus mitigating problems associated with light pollution and enhancing our well-being. MicroLED displays promise higher resolution, increased brightness, efficiency and never before possible compact light engines. We will talk about the latest Lumileds technologies enabling digital light sources and new applications.

The developments of high performance 1-10 micron size InGaN based RGB MicroLEDs are discussed. Through novel epitaxial growth and processing, and transparent packaging we have achieved external quantum efficiencies as high as 58% EQE at 450nm for microLEDs. The critical challenges of µLEDs, namely full-color scheme, decreasing pixel size and mass transfer technique, and their potential solutions are explored. Recently, we have demonstrated efficient microLEDs emitting in the blue to red at dimensions as small of 1 micron. Using strain relaxation methods we have also extending the wavelength range of the InGaN alloys as into the red with emission as long as 640nm. Red InGaN based red MicroLEDs with efficiencies of 6% has been fabricated, and they display superior temperature performance in comparison to AlGaInP based devices. This work was supported by the Solid State Lighting and Energy Electronics Center(SSLEEC) at UC Santa Barbara.

Epitaxy, a process for growing single-crystalline overlayers on wafers, has advanced the commercial deployment of high-quality heterostructured electronic and optoelectronic devices. Recent increasing demand for multifunctional, high-performance devices on a single chip has driven a technological shift from miniaturization towards high-density hetero-integration. This transition has catalyzed the evolution of stamping-printing and transfer-assembly techniques [1]. One strategy for heterogeneous integration utilizes transfer-based assembly methods, which entail the delamination of epi-layers fabricated through various batches and procedures. This approach grapples with two significant technical challenges in achieving high-density integration of high-performance devices (i.e., fabrication of micro-LED displays for AR applications). First, traditional epitaxial growth methods result in epi-layer devices strongly bonded to the substrate, complicating their separation without the use of high-power laser irradiation or chemical etchants. These separation techniques, known to inflict damage to both the substrate and epi-layers, impose strict constraints that limit enhanced device performance and productivity [2]. Second, during the transfer and assembly process, different functional devices must be segmented into tiny chips prior to their accurate transfer and assembly onto the target surface (or substrate). Even small misalignment during chip bonding to backplane circuits can disrupt device interconnects with the underlying layouts, thereby increasing the manufacturing costs of micro-LED displays. Additionally, the fabrication of higher-density vertical stack devices poses a formidable challenge, relevant not only for high-resolution display production (such as augmented reality (AR) and metaverse devices) but also for hetero-integrated electronics. In this presentation, we explore innovative epitaxy techniques (i.e., remote and van der Waals epitaxy) that eliminate chemical bonds between the epi-layer and the wafer [3-5]. This approach provides a potential solution via the straightforward delamination of epi-layers and their subsequent stacking, enhanced by meticulous photolithographic patterning procedures [4]. We will highlight our recent work on high-density, heterogeneously integrated vertical R/G/B micro-LEDs and flexible devices, leveraging these novel epitaxy methods, and emphasize potential applications in AR [6]. The remote epitaxy of spatially isolated micro-crystal LEDs has facilitated the fabrication of deformable lighting devices [7]. This emergent bond-free epitaxy could be readily adopted to extend the reach of semiconductor manufacturing, potentially leading to a heterogeneous system on a chip for comprehensive electronic and optoelectronic solutions. References [1] J. A. Rogers et al., Science 327, 1603 (2010). [2] H. Kum et al., Nat. Electron. 2, 439 (2019). [3] H. Kim et al., Nat. Rev. Methods Primers 2, 40 (2022). [4] Y. Kim et al., Nature 544, 340 (2017). [5] Y. J. Hong et al., Nano Lett. 12, 1431 (2012); Y. J. Hong and T. Fukui, ACS Nano 5, 7576 (2011). [6] J. Shin et al., Nature 614, 81 (2023). [7] J. Jeong et al., Sci. Adv. eaaz5180 (2020); J. Jeong et al., Nano Energy 86, 106075 (2021).

InGaN red LEDs are the key devices to realize AR and VR displays. We have developed InGaN single-QW red LEDs. The InGaN red LEDs show good I-V characteristics. The built-in voltage was only Vb=2.4 V. The peak wavelength at 2.4 V was 641 nm, therefore, the ratio of the photon energy to eVb was as high as 80%. Even at the 20 mA operation, the necessary forward bias was as low as 2.96 V. The light output power density was as high as 0.87 W/cm2 at 20 mA. Therefore, it shows a high WPE of 2.9% at 20 mA.

Opto-electrical characterization of LEDs/OLEDs is of essential importance for thorough understanding of light generation and emission properties of light emitting materials as a response to an applied electric current. The combination of photoluminescence (PL) and electroluminescence spectroscopy techniques can reveal the relationship of structure-lighting properties of novel LED/OLED materials and whole devices. Without doubts, this can help to optimize the composition and as a result the performance (brightness, lifetime, color) of these devices.

LED technology offers significant advantages over halogen and arc lamps in medical imaging due to long lifetimes, ruggedness and potential efficiency. However, LEDs have limitations, limited irradiance and efficiency degradation. Luminescent Concentrators (LCs) present a promising solution as they benefit from LEDs strengths whilst providing high theoretical efficiencies, brightness and generation of new wavelength components. This work introduces a novel approach of achieving a white light source using LED-pumped LCs. By combining various fluorophores, LCs can emit an optimal spectral output for multispectral applications such as endoscopy. The performance of this white light source is evaluated against traditional methods, xenon and halogen lamps, proving its potential as a replacement for aging technologies in medical imaging.

Growth of IIIN microLEDS on Si(100) substrates would enable direct integration with Si based CMOS. An oxide buffer is used to translate the crystal symmetry so that GaN(0001) can be grown on Si(100) in a wurtzite form. InGaN quantum dots (QDs) are presented as a novel solution to obtaining a red LED from the III-N material system. An engineered bottom contact is demonstrated by the addition of an epitaxial metal layer below the QDs.

MicroLED displays fabricated from compound semiconductor materials are a disruptive new technology offering advantages in efficiency, brightness, resolution and power consumption over incumbent LCD and OLED approaches. Today, such displays are assembled from arrays of micron sized emitters, made from traditional LED materials such as GaN (blue/green) and red (GaAs). And whilst an all GaN RBG solution remains the goal of the industry, this affording many advantages in display manufacture, producing high efficiency emitters at longer wavelength remains a challenge in GaN, so instead, device manufacturers use indium gallium phosphide (InGaP) to fabricate red microLEDs. In this work we present on a new 200 mm wafer platforms form for red microLED epitaxy where active structures are deposited on to CMOS fab compatible germanium substrates. Germanium is an excellent substrate starting material for epitaxial growth given it is lattice matching to GaAs, very high levels of crystal quality as well as mechanical strength and flatness. Here we compare the quality and performance of microLED devices grown on both GaAs and Ge and discuss the fab adoption strategies which are creating opportunities for the insertion of Ge based microLEDs into RBG displays We also discuss how these results create a path for large-scale microLED production on 300 mm platforms, integrated with CMOS backplanes to deliver the low cost, scaled approach which will be essential for the mass adoption of compound semiconductor based microLED displays.