The developments of high performance InGaN based micro-light-emitting diodes (µLEDs) 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 MmicroLEDs. 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 green at dimensions as small of 1 micron. Red InGaN based red MicroLEDs with efficiencies of 2.5% has also been fabricated.

We can grow high-In-content InGaN-based red LED structures by our original MOVPE. Using commercial InGaN-based blue and green LED wafers, we have fabricated RGB micro-LEDs and RGB monochromatic 10 X 10 micro-LED arrays. The size of the micro-LED was 17 m square. The red array showed the peak wavelength at 630 nm and the FWHM of 62.9 nm at 50 A/cm2. Its light output power density was as high as 176 mW/cm2, and the absolute EQE was approximately 0.4%. The RGB micro-LED arrays covered as good as 81.3% of the Rec. 2020 color space in CIE 1931 at 50 A/cm2.

We will give an overview of state-of-the-art results and challenges to achieve high-performing III-nitride vertical-cavity surface-emitting lasers (VCSELs), with a particular focus on the requirements to push the emission wavelength into the ultraviolet (UV). Our method to simultaneously achieve high-reflectivity mirrors and good cavity length control by electrochemical etching enabled the world’s first UV-B VCSEL. The use of dielectric mirrors yielded lasers with a very temperature-stable emission wavelength thanks to the negative thermo-optic coefficient of the mirrors. We have used the same etch methodology to also lift-off fully processed LEDs from their growth substrate to improve the light extraction efficiency.

Far-UVC LEDs are interesting for applications such as skin-tolerant inactivation of multiresistant pathogens and gas sensing. We present the development of 233 nm AlGaN-based far-UVC LEDs with an emission power of 3 mW at 200 mA and L50 lifetime of more than 1000 h, after burn-in. Additionally, the design of a far-UVC LED-based irradiation system, with a spectral filter which supresses emission >240 nm, to study the inactivation of bacteria and skin compatibility of the radiation will be presented. The system can be used to homogeneously irradiate a target area of 70 mm diameter with a mean irradiance of 0.4 mW/cm².

Surface disinfection has taken on a new role in the context of the corona pandemic. UVC modules based on LED chips strive to replace mercury vapor lamps. However this will only be achieved if the necessary optical performance for disinfection can be guaranteed. We would like to present the development of potting materials for UVC LED chips. The aim was to find a potting material for use at a wavelength of 250 nm, which is sufficiently transparent, easy to process and which remains stable in its properties for many 100 hours at these wavelengths. Furthermore, the total reflection in the LED base body should be minimized by a refractive index of the cured material n >> 1.4. In addition to the aspects of material development, metrological requirements and long-term studies are also presented. We have succeeded in developing a potting technology that can greatly increase the performance of the UVC LEDs by up to 70%.

We present LED profiting from the bottom-tunnel junction (BTJ) construction. The BTJ design aligns the polarization fields in a desired direction in the vicinity of active region and inverts the ordering of the layer stack in the structure. This leads the situation were conductive, n-type layer is on the very top of the structure. Since current spreading in n-type material is much better than in p-type, BTJ-based light emitters open new possibilities in heterostructure design. In this talk we present new light emitting structures grown by plasma-assisted MBE based on BTJ platform and compare prospects for bottom and top tunnel junction devices.

Nanometer- and Micrometer-scale LED arrays are useful not only for display applications, but also for specialized applications like lens-less microscopy, mask-less lithography or optogenetics. In these contexts, the spatial resolution of the optical field and precise control over the illumination pattern at the object plane is of special importance. We have studied numerically different GaN LED array designs, calculating light extraction, optical near field and crosstalk between pixels. We find that 3D-patterning can help in shaping the light emission, while optical crosstalk becomes a critical issue for small LEDs and pitches below 300 nm.

High-speed optical wireless communication (OWC) systems based on light-emitting diode (LED), such as Li-Fi, are promising solutions for the looming spectrum crisis in 6G wireless communications. OWCs typically extend the RF spectrum by harnessing the visible light and infrared spectra, but the recent advancements in deep-ultraviolet (DUV) LED device technology allow us to further extend the OWC spectrum down to the DUV range, namely the solar-blind band. This talk reviews the recent progress of the high-speed OWCs based on DUV-LEDs including Gbps-class transmission demonstrations in direct sunlight and analyses on the microscopic structural and optical characteristics of high-speed AlGaN-based LEDs.

The focus of LED technology and product development is expanding from emitter-level performance to enabling application-level differentiation. Over the past decade, the focus on LED efficiency has brought tremendous societal benefits and accelerated development. With the industry’s rapid progress, the rate of gains in lm/W for the dominant technology based on phosphor-converted LEDs has slowed. New technologies such as phosphors with narrow emission spectra and highly efficient ‘direct’ color LEDs are needed to reach the next levels in light source efficacy. At the same time, LED products are reaching new levels of complexity and functionality. CMOS/LED hybrids incorporate driving and other functions into LED-level packages are poised to bring intelligent, adaptive light sources to applications. MicroLED is the next frontier for displays and requires new ideas across all aspects of LED technology. This wave of innovation makes it one of the most exciting times for the LED industry.

Widening the range of efficiently emitting wavelengths is a goal of ongoing research on III-nitride LEDs. The so-called green gap is mainly related to the increasing severity of efficiency droop as the wavelength increases. The peak EQE in commercial green LEDs exceeds 60% but corresponds to a very low current density. In this presentation we review challenges in the development of long wavelength III-nitride LEDs. We discuss possible strategies to mitigate droop based on the understanding that nonradiative Auger recombination is the root cause. Finally, we present the current efficiency status of green, yellow and red III-Nitride LEDs.

In this presentation, we will discuss the requirements for Red microLEDs for advanced displays, the corresponding MOCVD Epitaxy capability needs,and share Veeco’s recent learnings.

Quantum Dot technology is playing an increasingly important role in emissive displays including OLEDs, microLEDs and direct view emissive QD-LEDs. Applying Quantum Dot Color Conversion (QDCC) to blue OLEDs or microLEDs, can lead to lower cost, brighter, high contrast displays with wide color gamut. Nanosys has developed new, heavy metal-free QD materials with enhanced blue absorption, high quantum yield and narrow, tunable emission. These attributes enable the fabrication of patternable QDCC films with high (>35%) photon conversion efficiency and BT.2020 color gamut coverage. These new QD materials have delivered greater flexibility to the design of printable inks and formulations. Fabrication can be done using inkjet printing or photolithography, depending on the feature size, mass production and cost requirements of the display product.

Not many phosphor materials can offer stable output under high incident light intensities. Even the most promising LED phosphors saturate in high-power applications, i.e. they show decreased light output. The saturation behavior is often poorly understood. Here, I will present the efforts of Utrecht University and the lighting company Seaborough Research to unravel the saturation mechanisms of the popular commercial LED phosphor materials CaAlSiN3 doped with Eu2+, and K2SiF6 doped with Mn4+. Experiments with square-wave modulated laser excitation reveal the dynamics of absorption and decay of the luminescent centers. By modeling these dynamics and linking them to the saturation of the phosphor output intensity, we distinguish saturation by ground-state depletion, thermal quenching, and ionization of the centers. We measure and model the effects of external heating and heat transport to the environment.

The importance of automotive lighting increased sharply over the last two decades since LED based systems have been introduced successfully. Besides the recent outstanding developments for traffic safety, also design and energy efficiency aspects are getting more prominent. To fulfill the increasing set of specifications, the presented functional polymers are essential for the further development in automotive lighting solutions. Already qualified for high precision bonding tasks in automotive lighting applications, the discussed materials are also capable to manufacture Micro Lens Arrays (MLA). Moreover, they allow the design of smaller and more efficient systems as well as the implementation of additional functions.

Micro-LED has excellent technical advantage, and the manufacturing cost is getting reduced. To be mainstream technology, the next bottle neck is the testing cost. The existing test approach has issue of performance, accuracy and throughput then it is impacting entire manufacturing cost. One of issue on test is the EL optical test performance and throughput which test LED one by one. There is strong demand want to the optical test die in parallel but should meet mass production performance. This presentation offers brand new approach of the micro-LED wafer testing especially for upcoming Mass Production. Which has electrical/optical test embedded as single setup, massive parallel test of electrical/optical test with excellent throughput. Also this approach could use for matrix/unit testing.

InGaN/GaN core-shell microrods (µrods) are highly promising for a new generation of light-emitting diodes. We present a 3D confocal optical approach with a spatial resolution <500 nm for characterizing operating µrod devices. 3D photoluminescence maps reveal an inhomogeneous emission: red luminescence originates from the apex and green emission from the corners, while blue emission dominates at the sidewalls. A pronounced photocurrent is measured while exciting µrods in closed current configuration, indicating charge carrier losses out of the active region due to tunneling. This interpretation is confirmed by applying an external voltage, where losses are suppressed.

In a light emitting diode-based semiconductor light source that is variously applied as a display light source, luminous efficiency is a very important optical property, and various research methods including multiple quantum wells have been proposed to increase the luminous efficiency. However, since the efficiency improvement is basically based on the planar structure, there was a limit to the improvement of optical properties. In this study, nano holes were formed through micro patterns and etching of silicon oxide, different from the conventional structure are proposed. In addition, it is possible to implement a nano sized columnar structure through nano holes of silicon oxide, and by depositing a light emitting layer on the nano structure, it is intended to present a semiconductor light source having a nano-sized light emitting structure.

We demonstrated the 630-nm peak wavelength InGaN-based micro-LED arrays at a high current density up to 50 A/cm2. The device dimension was 17 × 17 µm2. The micro-LEDs obtained a high light output power density of 1.76 mW/mm2 at 50 A/cm2, which is much higher than AlInGaP-based micro-LEDs (20 × 20 µm2). The on-wafer EQE was 0.18%. We also individually fabricated the blue and green micro-LED arrays, the color gamut of RGB micro-LED arrays covered as high as 81.3% of the Rec. 2020 color space in CIE 1931.

AlGaN light emitting diodes (LEDs) emitting in the deep ultraviolet (DUV) range typically suffer from poor light extraction efficiency (LEE). In this study, we determine the effects of nanostructure height, diameter, and emission wavelength on LEE. Changes to device morphology influencing surface to volume ratio (SVR) are studied in order to optimize device dimensions to maximize LEE. Simulations show improvements in LEE of up to 300% and 60% for structures with increased height and decreased diameter respectively, which is predicted for higher SVR structures. These results shows that engineering of nanostructure SVR could be used to improve DUV LED efficiency.

Although gallium nitride (GaN)-based electronic devices for next-generation have garnered increasing attention over the last few years, the formation of surface defects, which severely deteriorate device performances, is fundamentally unavoidable and surface passivation is highly desired. Herein, we report the realization of the clean van der Waals passivation layer, 2D hexagonal boron nitride (h-BN), directly grown on AlGaN/GaN HEMT wafer by using Metal-Organic Chemical Vapor Deposition (MOCVD) system. It was found that the hetero-interface between ~2.5 nm-thick h-BN and AlGaN layer is the atomically sharp with very weak van der Waals interaction, observed by state-of-the-art microscopic and spectroscopic analyses in consistent with calculations.The wafer-scale direct growth of atomically-thin-yet-electrically- “thick” h-BN would be very beneficial for miniaturization of not only compound semiconductor devices but also Si-based electronic devices.

The size-dependent variation of external-quantum-efficiency (EQE) has investigated by fabricating InGaN-based blue and near ultraviolet (NUV) micro light-emitting diodes (μ-LEDs) with mesa sizes from 10×10 μm2 to 250×250 μm2. We have compared the performances between blue and NUV μ-LEDs by measuring various optoelectronic characteristics, and found opposite trend between them. With reducing μ-LED sizes, the EQE of blue μ-LEDs decreases due to temperature-dependent efficiency droop which is consistently obtained by calculating the blueshift in peak-wavelengths and thermal-resistance. Contrary, the improved current spreading increases the light-extraction-efficiency which causes the EQE of small sized NUV μ-LEDs to increase.