Almost two decades have passed since the realization of complete 3D photonic crystals at optical wavelengths. During these years, the manipulation of photons by photonic crystals has progressed tremendously. For example, the concept of confining photons to a very small modal volume has been established and nanocavity Q-factors have exceeded ten million, enabling platforms for strong light-matter interaction and quantum information processing. Photonic crystals allow even a broad-area manipulation of photons, by which semiconductor lasers with a very bright, narrow-divergence beam and various functionalities including 2D beam steering have been realized. Such lasers are promising for applications in light-detection and ranging (LiDAR) and direct material processing, which are important for the forthcoming Society 5.0. Photonic crystals also enable thermal emission control, by which the issues of conventional thermal emission devices such as their extremely broad emission spectra and slow response speed have been fixed, and a renovation of thermal emission devices has been achieved. In this plenary talk, we will review such progress of photonic crystals including their social applications.

In the first part of this presentation, we will discuss recently emerging applications of the state-of-art deep learning methods on optical microscopy and microscopic image reconstruction, which enable image enhancement and new transformations among different modalities of microscopic imaging, driven entirely by image data. In this second part, we introduce a physical mechanism to perform machine learning by demonstrating a Diffractive Deep Neural Network architecture that can all-optically implement various functions following the deep learning-based design of passive layers that work collectively. We created 3D-printed diffractive networks that implement classification of images of handwritten digits and fashion products as well as the function of an imaging lens at terahertz spectrum. This passive diffractive network can perform, at the speed of light, various complex functions that computer-based neural networks can implement, and will find applications in all-optical image analysis, feature detection and object classification, also enabling new camera designs and optical components that perform unique tasks using diffractive neural networks.

Fully transparent deep ultraviolet light-emitting diode was realized by employing a polarization-engineered p-type AlN thin layer to serve as p-ohmic contact layer. External quantum efficiency and wall-plug efficiency of such a fully transparent 269 nm LED were measured to be 12.8% and 9.5% at 20 mA DC, respectively.

The role of dopants in AlN and dilute-As AlNAs alloys is investigated using First-Principle Density Functional Theory (DFT) calculations. DFT analysis reveals significant shift in the ionization energy of dilute-As AlNAs alloys with Magnesium dopant. Other dopants such as Beryllium and Calcium in dilute-As AlNAs alloys are also investigated for their ionization energies. Further details of the dopant capability in the dilute-As AlNAs alloys will be discussed.

In this work, we propose an EBL-free deep ultraviolet light-emitting diode (DUV LED) by employing linearly graded AlGaN quantum barrier (QB) in the active region. Simulation results show that compared with typical DUV LED containing an EBL layer, the graded QBs structure with increasing Al-composition along the growth direction (c-axis) can achieve higher output power and lower forward voltage through the manipulation of carrier flow. The carriers (electrons and holes) distribution, different grading profiles and output performance are analyzed to investigate the forming mechanism of the EBL-free DUV LED.

GaN-based ultraviolet laser diodes are investigated for potential applications like biochemical detection. The AlGaN/InGaN multiple quantum wells are epitaxially grown by using metal-organic chemical vapor deposition (MOCVD) system. The device structure is redesigned to get a better optical confinement effect as well as the suppression of electron leakage current. The ultraviolet laser diodes on GaN substrate are fabricated with a stimulated emission peak wavelength of 392.9 nm and a threshold current density of 1.5 kA/cm2. Under a room-temperature continuous-wave operation, the output light power of 80 mW. Another laser diode with a shorter stimulated emission peak wavelength of 381.9 nm is then fabricated. The threshold current density is 2.8 kA/cm2. In order to demonstrate the ultraviolet laser diodes with shorter wavelengths, growth mechanism of AlGaN/InGaN MQWs with peak wavelength around 370 nm are studied.

The performance of deep UV LEDs is studied with respect to the impact of extended and point crystal defects. Applying high temperature annealing, AlN base layers of reduced dislocation density were fabricated and used for UV LEDs. Moreover, the level of point defects such as hydrogen and magnesium are varied by the doping level and thermal activation conditions. The efficiency and stability during long-term operation is investigated for general conclusions on the further optimization of the devices.

After many years of R&D work on LED module development, a discussion on different factors influencing the reliability of LED moduls will be given. Degradation effects are shown depending on LED design itself as well as the device architecture. A burn-in process leads to an optical power loss of many percent until the power is leveled at a certain value. In some cases the optical power seems to be enhanced. These effects will be discussed using selected examples and and will be evaluated on the function of the UV lighting unit. The influence of the joint for electrical contacting of UV-LEDs is validated, as well.

Deep ultraviolet (UV) light emitting diodes (LEDs) have a wide range of applications. Typically, ceramic packages are used. Comparative thermal simulations show that Si compared to aluminum nitride does not necessarily impair thermal management. The advantage of the Si packing due to the possibility of integrating functional components has been worked out. The first samples with integrated protection diode, an optimized reflector and an optically adjusted single and multiple Fresnel lens are presented. The Si packages are designed for the flip-chip technology of UV LEDs with SnAg soldering, thermo-compression or thermosonic bonding and Ag-sintering.

Technology development of blue, green and red light micro LED display (uD) was developed in this study. Here, 64 x 32 pixels on the display, with size of 50 μm x 50 μm and pixel pitch of 100 μm were demonstrated. ITO as transparent conducting layer on the P-epilayer is used to be contact layer and contributes current spreading. These uDs were fabricated into the passive matrix array and driven by PWM under 5 V. The 430, 590 and 600 nit for blue, green and red uDs were obtained as the uDs driven by PWM at 5 V.

Sub-wavelength sized nanoLEDs are good candidates for highly localized light sources, which could be used for super-resolution illumination in novel imaging systems. In this work we present electromagnetic simulations of the emission pattern of realistic InGaN/GaN nanoLED arrays. We show the impact of optical coupling between neighboring pixels, and discuss ways to overcome optical crosstalk and to reduce spatial extension of the optical near field. We also present estimations of the far field in presence of different nanometer sized objects on top of the emitter array.

This study is to produce three-dimensional structure by applying nano-mold process. The three-dimensional structure can be more suitably provided through a nano process using a patterning and etching process. The nano-mold process enables multiple wavelength light emitting diode. The nanorod structure through nano-mold technology is suggesting the new characteristics of nano structure by the way of realizing the light emitting diode of three-dimensional structure. The light emitting area will also be enlarged through changing three-dimensional from two-dimensional structure.

Nanotechnological approaches have been widely explored for improved light output in InGaN/GaN light emitting diodes (LEDs). In this talk, I will introduce the application of SiO2 nanoparticle (NP) embedded in GaN nanopillar template for high optical extraction, of Ag/SiO2 core/shell NP for a localized surface plasmon (LSP) LED, and of porous GaN templates made by combined wet chemical etchings. With the SiO2 NPs placed between the GaN nanopillars, subsequent overgrowth of GaN layer started only on the exposed tips of the nanopillars and rapidly switched to the lateral growth mode. This resulted in a high quality GaN layer sitting on the nanopillars and the layer of pores formed over the SiO2 nanoparticles. For LEDs grown on top of such template, ~3 fold increase in optical output was observed compared to reference samples. The effect is attributed mainly to the improved light extraction efficiency due to additional scattering in the nanopillars-SiO2-pores portion of the structure, also to the increased internal quantum efficiency caused by a decreased dislocation density and relaxed strain due to the GaN nanopillars. Practical approaches to making LSP-LEDs will be discussed. The stability problem of NPs could be solved by developing the technology of Ag/SiO2 core/shell NPs prepared by sol-gel method. The NPs places the LSP resonance peak near 450 nm matching it to the blue MQW LEDs. It is demonstrated that strong PL intensity enhancement can be achieved for MQW structures with Ag/SiO2 NPs. These studies seem to indicate that the extent of efficient spatial coupling covers the range of about 40 nm, in agreement with earlier calculations for Ag NPs. Measurements of the LSP-related PL enhancement stability over time due to Ag/SiO2 core/shell NPs is better than for Ag NPs. Free-standing GaN LED structure with high crystalline quality was fabricated by combining electrochemical and photoelectrochemical etching followed by regrowth of LED structure and subsequent mechanical detachment from a substrate. The structural quality and composition of the regrown LED film thus produced was similar to standard LED, but the PL and EL intensity of the LED structures on the etched template were several times higher than for standard LED. The performance enhancement was attributable to additional light scattering and improved crystalline quality as a result of the combined etching scheme.

Inorganic-based micro light-emitting diodes (μLEDs) have been considered to substitute the conventional displays, because of their outstanding properties. The μLED applications are widely extending to various fields, such as augmented reality (AR), smart and biomedical devices. Furthermore, flexible μLEDs have been extensively investigated by several researchers for user-friendly optoelectronics. However, the μLEDs stability in harsh environments were not significantly investigated yet. Here, we realized wearable μLEDs using simple and rapid μLED fabrication process. Flexible μLEDs have excellent mechanical, thermal, humid, and photo stability in various environmental conditions. Finally, wearable μLED array was achieved on a general cloth.

Pinhole-shaped LED arrays with dimensions ranging from 100 µm down to 500 nm have been developed as separately controllable point illumination sources. The proposed microLED arrays, which are based on gallium nitride (GaN) technology and emitting in the blue spectral region (λ= 465 nm), are integrated into a compact lensless holographic microscope for a continuous, non-invasive, label-free cell sensing and imaging. From the experimental results using single pinhole LEDs having diameters of 50 μm, the reconstructed images display better resolutions and enhanced image qualities compared to those captured using commercial surface-mount device (SMD)-based LED.

Blue light emitting diodes (LEDs) exhibit internal quantum efficiency exceeding 90%. This is the consequence of the unique property of InGaN/GaN quantum wells (QWs) to emit light despite a high density of dislocations. This is ascribed to carrier localization in potential fluctuations induced by InGaN alloy disorder. On the other hand, high efficiency blue LEDs feature an InGaN layer underneath the active region. In this talk, we will show that the role of the InGaN UL is to incorporate defects at the GaN surface, which critically impact the InGaN/GaN QW efficiency. An origin of those defects will be proposed.

In the past decade, GaN-based LEDs have emerged as excellent devices for application in many fields, including lighting, automotive, sensing, sterilization, communication, biomedical treatment, printing, displays, agriculture. In all these fields, reliability is a critical requirement, and important efforts have been done to optimize the robustness of these devices. In this paper we will review our most recent results in the field of GaN LED degradation physics, by identifying the most relevant degradation mechanisms: 1. The generation of non-radiative recombination centers within the active region of the devices, due to the flow of highly energetic carriers through the junction 2. The recent demonstration of a recombination-driven degradation process, that results in the generation of defects in the active region 3. The properties of the defects responsible for non-radiative recombination, whose concentration increases after stress time 4. The degradation processes of UV LEDs submitted to current stress tests, and the related kinetics The results described within this paper provide information on the physics of the degradation processes, and guidelines for the design of reliable GaN-based LEDs.

We investigate the electroluminescence of blue LEDs in low bias (500 pA – 9 μA) at different temperature (15 °C – 75 °C). From 500 pA to 100 nA, the OP increases with bias current up to 10nA, and is stronger at higher temperature, as expected by radiative recombination through deep levels. The stronger contribution is at λ > 800 nm, i.e. at energies lower than the QW and GaN barrier midgap (720 nm). Above 100 nA the OP increases with current, and is compatible with QW emission. Its intensity decreases at higher temperature, as expected for non-radiative recombination. The experimental findings indicate that radiative recombination through deep levels can significantly influence the low current characteristics of the devices, even when those states are not at midgap.

Polarization-matched InAlN/InGaN MQW designs have been studied by using the modern theory of polarization with hexagonal reference. The characteristics of InAlN/InGaN polarization-matched MQW LEDs with various QBs and QWs were investigated. A polarization-matched In0.33Al0.67N/GaN MQW structure was specifically designed by leveraging strain and bandgap. After optimizing the number and thickness of QWs, the 425 nm LED has relative IQE of 56% and efficiency droop of only 7% at high current density of 333 A/cm2. The results indicate that the In0.33Al0.67N/GaN polarization-matched MQW LEDs have great potential in general lighting applications.

Presence of a cavity array embedded in LED structures is beneficial in obtaining the improved crystal quality due to lateral overgrowth, the relaxation of compressive stress and reduced wafer bow, and the improved light extraction due to maximum index contrast. In this presentation, the cavity-engineered sapphire substrate (CES) technology to improve the external quantum efficiency of light emitting diodes will be introduced. Fabrication of sapphire nano-membrane formed by solid-phase epitaxy of amorphous alumina deposited on photoresist patterns allowed us to design the shape and position of cavities. The effect of cavity array in light extraction was theoretically and experimentally evaluated to confirm that the cavity effect.

InGaN-based resonant-cavity light-emitting diode (RC-LED) structure with an embedded 1/4λ-stack nanopipe-GaN/undoped-GaN distributed Bragg reflectors (DBR) structure have been demonstrated. High refractive index Si-heavily doped GaN (n+-AlGaN:Si) epitaxial layers are transformed into low effective refractive index nanopipe AlGaN layers in the n+-AlGaN:Si/u-GaN stack structure through a doping-selective electrochemical and a lateral wet etching process. The anisotropic optical property of the nanopipe structure in the DBR structure provides an anisotropic and polarized high light reflectance spectra from ultra-violet to green light regions. The central wavelength blueshifted property with a high reflectivity stopband was observed in the angle-dependent reflectance spectra of the nanopipe DBR structure similar to conventional dielectric DBR structure. Ultra-short cavity length in the GaN-based resonant-cavity light-emitting diode had been realized by using the embedded and conductive nanopipe DBR with a narrow divergent angle property. Narrow linewidth, single cavity mode, and high linear polarized light are observed in the GaN-based RC-LED with an anisotropic nanopipe DBR structure which has the potential for the linear polarized vertical cavity surface emitting laser applications.

LED components today are complex systems with many optical, electrical, thermal, mechanical and transport interactions. These interactions imply to consider the LED component as a system, in order to identify potentials and remove deficits and improve the LED. Extensive research and development of last year’s allows to reach a high efficacy for LEDs – in the general lighting – of over 200 lm/W, and become commodity in the lighting market. In order to achieve higher efficacies, considering all mentored interactions is necessary. This talk gives an overview of system architecture of LED component today and shows projections into the future.

Adaptive Driving Beam (ADB) applications are proliferating from premium vehicles into the mainstream car models with LED technology creating the inflection point enabling cost effective digital headlighting to replace light steering by electro-mechanical swiveling shutters. Today’s LED matrix solutions support the mainstream ADB functionality with 10-25 independently addressable pixels. Meanwhile, the premium segment is evolving to a pixel count in the thousands to million range driven by additional functional value in beam content. Given the usual functionality migration from premium to mainstream segment we can anticipate the adoption of increasing pixel count ADB solutions in the mainstream to support increased functionality, but at the appropriate cost point. Given the emerging range of high pixel count solutions today and an equally wide range of emerging technologies which support these, it would be useful to shed light on which of these solutions have the potential to meet the mainstream requirements. This is the motivation for the work presented in this paper. We will look at all of the major competing technologies and offer an analysis on which technologies could support the requirements to enter the mainstream and based on this, predict the leading solutions with clear justifications. This will allow us also to forecast which new ABD functions are most likely to make the transition from premium to mainstream.

SLD Laser is commercializing a new generation of visible laser light sources with more than 10 times the luminance of LEDs. These sources utilize the company’s proprietary and patented semipolar GaN laser diodes, combined with advanced phosphor chip technology, and novel high luminance packaging. Utilizing this laser pumped phosphor architecture, the sources deliver safe, high luminance white light output, enabling superior optical control with miniature optics and reflectors, along with high efficiency fiber optic transport and waveguide delivery. We will report on the performance of these devices and describe their early adoption into specialty lighting, automotive, biomedical and industrial applications.

Laser-scanner headlamps, based on a blue laser spot steered by a MEMS mirror over a converter, can illuminate the road flexibly and efficiently. Some existing demonstrators suffer from insufficient performance of the converter (low contrast) or of the MEMS mirror (lack of flexibility). With a new high-contrast converter and high-performance MEMS mirrors, we have developed improved laser-scanner demonstrators optimized for different functions like full adaptive driving beam or visualization (symbols, guiding lines, and text). We explain the system design, converter technology, and high-bandwidth MEMS control, show the performance in video sequences, and discuss future applications of such systems.

Automotive headlight evolved from incandescent, to halogen, to xenon, to LED, and most recently, to laser phosphor lamps with increasing efficiencies and brightness. This paper presents the development of laser phosphor headlights using glass phosphor and single crystal phosphor for efficient and high power operations. Laser diodes are used for pumping the phosphors producing the white light to be projected to the roadway. In addition, various configurations of the laser diodes, which are individual addressable, are to be presented. Together with the used of DLP and LCD imagers, intelligent headlights are developed with the abilities selectively scanning the imagers illuminating the roadway with varying intensities. The design of the systems and the experimental results will be presented.

Ultrasonic mechanical vibrations in solids are widely used in non-destructive testing, and high-power applications such as ultrasonic welding or soldering. The visualization of ultrasonic wave propagation in transparent solids is helpful for understanding the ultrasonic behaviours. The classical method of photoelasticity allows the visualization of the static stress distribution in birefringent materials. Utilizing recent high-power LEDs in the photoelasticity allows to capture dynamic stresses by high frequency stroboscopic light. High frequency stationary and transient oscillation processes in elastic solids can be visualized with this method. The designed LED array in this paper has a dimension of 210 mm×300 mm, and every LED has distance of 38mm to each other, and the light intensity has a homogeneity value. The temporal and spatial resolution of stress-optic systems depends mainly on the dynamic properties of the lighting technology used. The high speed synchronization of the stroboscopic light sources results in a high temporal resolution of the photoelasticity analyses. This enables the photoelastic investigation of highly dynamic load conditions, such as transient vibrations and contact processes.

LEDs can be modulated at relatively high speeds to support wireless optical data communication (OWC / LiFi). We use non-linear differential equations for photon emissions in the LED to derive a discrete-time equivalent model with delays and non-linearities. This can be inverted, in the sense that we can actively mitigate the non-linear dynamic LED distortion by adequate signal processing. We characterize and measure commercially available illumination LEDs. Moreover, we address the performance of the OWC equalizer base on these models, in which the system needs to find and converge to the appropriate compensation settings.

With this work we report on the design, development and testing of near UV LED-based systems for oxygen gas sensing. The design and developed system is an optoelectronic setup based on 405 nm LEDs which excites and measures the photoluminescence emitted from a porphyrin based luminophor. By means of an accurate optical and optoelectronic setup, the system is able to operate without the need of avalanche photodiodes, thus resulting in a compact and low energy structure. The optical setup is specifically designed to maximize both the LED light exciting the luminophor and converted light acquired from the sensor.

In order to obtain low resistive GaN-based tunnel junctions, various approaches have been proposed so far, such as using polarization charges, high doping, and interface treatments. One of the remaining important factors should be impurity profiles. We investigated and optimized the impurity profiles in GaN tunnel junctions. We found that a larger overlap between a high Mg region and a high Si region (both over 1e20 cm-3 ) was very important to obtain low resistance. Our MOVPE-grown GaN tunnel junction shows the differential resistivity of 2.4×10-4 Ωcm2 at 5 kA/cm2, comparable to that of our GaInN tunnel junction. This work was partly supported by MEXT GaN R&D Project.

AlInN alloys are promising as cladding layers in GaN-based laser diodes (LDs) because they show a large index contrast to GaN or InGaN at an alloy composition lattice-matched to GaN. For realizing AlInN cladding layers, a sufficiently-thick film with a smooth surface is necessary. In this study, we grew 300-nm-thick AlInN films on a c-plane GaN/sapphire template or a free-standing (FS) GaN substrate by metalorganic chemical vapor deposition (MOCVD). The results showed that smooth surface roughness of approximately 1.8 nm and 0.5 nm in RMS were obtained for the AlInN films grown on GaN/sapphire and FS-GaN, respectively.

A one-step MOCVD process for 2D WS2 and 2D MoS2 on sapphire substrates in a commercial AIXTRON planetary hot-wall reactor was developed to control nucleation and lateral growth. A fine-tuned S-to-metal ratio inhibits the parasitic deposition of carbon contaminations. WS2 deposition experiments show that to achieve a fully coalesced 2D film, a sufficient amount of WCO, the limiting species during growth, is necessary. A WCO flow of 20 nmol/min allows substrate coverages >50 % in 10 h. Extending the growth time to 20 h results in deposition of fully coalesced monolayer WS2 without carbon contaminations and only sparse bilayer nucleation showing strong PL.

In order to grow large diameter (e.g. 200 or 300 mm) GaN-on-Si LED epiwafers for micro LED applications, precise strain-engineering is crucial not only to achieve excellent emission uniformity and low bow but also to achieve high processing yield without cracks and wafer breakage. In the presentation, we would like to demonstrate how precisely and repeatable we can control the strain on large GaN-on-Si LED epiwafers with ALLOS’ unique and patented epi-technology. Furthermore, we would like to propose in-line strain-engineering during epitaxial growth to enable reproducible emission uniformity.

Quantum Dots are changing the way displays are made. Today, this unique nanomaterial is perfecting LCD displays, enabling a new generation of brighter, more efficient televisions with lifelike colors. This has given LCD technology an important edge as it battles new TV display entrants such as WOLED. What’s next for this novel nanotechnology? This talk looks at how quantum dots are the future technology platform for displays including their evolving use in LCD displays, as well as how they enhance and are being used in OLEDs and micro-LED displays, and how they are being developed as emitter materials for future printable electroluminescent displays.

With the advancements of blue diode lasers and the phosphor materials, there is a tremendous progress in changing the high power visible light sources from discharge lamp based system to laser phosphor based system. This paper describes the development of the single crystal phosphor illumination module with red, green, and blue emissions, and becomes white when combined, with over 70 W of laser power handling capacity. This development includes the used of 2-dimensional laser array for excitation, phosphor crystal with special polishing and coatings, the use of diffusers, and the use of CPC, straight and tapered light pipes and light tunnels. Computer models and experimental results will be presented.

By placing Ag nanoparticles between blue-emitting (~465 nm) InGaN/GaN quantum well (QW) light-emitting diode and red-emitting (~620 nm) CdSe/ZnS quantum dots (QDs) for inducing simultaneous surface plasmon (SP) coupling with QWs and QDs, the QD emission intensity and the internal quantum efficiencies (IQEs) of both QDs and QWs can be enhanced. By comparing the samples with different Ag NP geometries, an Ag NP structure producing the localized surface plasmon resonance peak around the middle between the QW and QD emission wavelengths leads to the maximum QD IQE enhancement.

There is an increasing need for high power density light sources, e.g. for the next generation of car headlights, diode laser pumped white light sources and projection devices. However, saturation and droop at high excitation densities limit the light output in high power devices. In this presentation a basic overview of known luminescence quenching processes will be followed by a discussion on how we can increase our understanding of luminescence quenching with a focus on high power applications. New experimental and theoretical capabilities will be discussed that may help to acquire insight in what limits the light output in current and future light sources.

High flux applications with limited etendue request higher luminance values than available from LEDs (<200 Mnit). This paper evaluates light engine concepts based on luminescent converters pumped by laser diodes, and concepts based on luminescent concentrators pumped by LEDs. Both meet the required brightness conditions. With static converters irradiated by laser diodes, 40 klm (650 Mnit) yellow emission was achieved. With green light concentrator modules, peak fluxes at 50% duty of >25 klm at 1-1.5 Gnit have been achieved, while thermal conditions are much more relaxed than for LD-based systems. Both concepts peak in different parts of the application spectrum.

In solid state lighting there is a strong focus on making still smaller and more compact light sources with high luminous performance. For these high-lumen density applications laser excited light sources become favourable since blue laser diodes do not suffer from phenomenon called efficiency droop typical for LEDs. For white light generation blue laser radiation has to be partially but converted by an efficient phosphor. Standard powder phosphors are not capable to withstand high thermal load caused by Stokes shift due to encapsulation in silicone resins which significantly limits heat dissipation. We present a solution with monocrystalline phosphor which is an excellent convertor from blue to green, yellow and yellow-orange colour. With internal quantum efficiency over 95% up to 250°C, high thermal conductivity (~10 W/m.K) and luminescence thermal quenching starting over 200°C it poses new opportunities in light design. But even employing highly efficient monocrystalline phosphor with multiple high power laser diodes can lead to overheating and then thermal management become crucial. We have developed solutions based on principles of metal soldering which assures the most efficient connection of the phosphor to the copper or aluminium heat sink to deal with the heat. Last but not least the question of colour quality rises. Since the emission of the converted light is omnidirectional, when employing coherent directional laser light the speckle patterns and hallo effect has to be taken into the account. By enhancing the surface of the phosphor with defined structures above mentioned phenomena are suppressed together with the positive effect on external quantum efficiency of the phosphor.

Lighting applications that require luminance levels above several 100 cd/mm² cannot be addressed with LEDs today. Laser pumped phosphor (LPP) light sources are an emerging technology that helps to address this field with solid state lighting (SSL). Digital projectors with a LPP light source are already commercially available. They make use of phosphor wheels that are irradiated with blue laser light to generate light via photo-luminescence. The power limit of the phosphor wheel is determined by the peak temperature of the phosphor at the laser spot. We present experimental and numerical studies on the temperature contribution of both, the wheel geometry and the phosphor material, and show that ceramic phosphor rings are the best choice for high power and high luminance applications. Results for power levels close to 700W and an irradiance above 180 W/mm² are presented.

The low growth temperature technology Remote Plasma Chemical Vapour Deposition (RPCVD) is currently being developed by BluGlass Ltd. for use in high-brightness LED applications. The unique growth conditions of RPCVD are demonstrated to produce Activated As-Grown (AAG) buried p-GaN for achieving GaN-based tunnel junctions (TJ) for use in current spreading and potential use in cascade LED and LD applications. Hybrid RPCVD/MOCVD TJs were grown on commercial full blue LEDs, and all-RPCVD TJs were grown on commercial partially completed blue LEDs and the devices were processed into 1.1 mm x 1.1mm chips. The LEDs with hybrid TJ displayed a 4.4% increase in light output power (LOP) and an increase in forward voltage (Vf) of 0.68 V compared to LEDs using indium-tin oxide (ITO) at a current density of 26 A/cm2. The LEDs with all-RPCVD TJs displayed a 3.6% increase in LOP and an increase in Vf of 0.88 V at 26 A/cm2.

Tunnel junctions grown by metalorganic vapor phase epitaxy (MOVPE) are a key technology to enhance top surface light emission of visible light emitters such light emitting diodes and vertical cavity surface emitting lasers. We developed a growth process that is conducted in one sequence without any ex-reactor treatment of the tunnel junction region. Crucial for this MOVPE growth are heavy Ge-doped n-type GaN layers and the activation process for the hydrogen passivated Mg acceptors. We further found a dependence of LED performance on the doping profile in the p-type GaN.Mg layer. For top surface emitting LEDs, the light emission is enhanced due to negligible absorption within the GaN:Ge layer. High-injection currents upto few kA/cm^2 have been obtained in small diameter circular mesas. While large area devices show comparable or even better IV characteristics at low current densities an increasing bias offset is noticed at current densities > 100 A/cm^2. Measurements of the internal quantum efficiency as a function of current density are currently performed to analyze this phenomenon. Application of such MOVPE-grown tunnel junctions to lasers and double-junction LEDs will be reported.

High quality GaN, AlN, InN, and their alloy have been prepared by pulsed sputtering at low substrate temperatures and used for fabrication of various optical and electron devices. Carrier mobilities of these films are not at all inferior to those prepared by MOCVD, which is indicative of growth of high quality materials. Successful low temperature sputtering growth of high quality nitride films makes it possible to fabricate low cost nitride LEDs and transistors on large area substrates such as metal foils and glass. These results indicate that sputtering growth is quite promising for producing of future micro LED systems.

Theoretical and experimental studies have revealed the importance of random alloy fluctuations in InGaN on optoelectronic properties of quantum well LEDs. In this study, we theoretically predict the effects of non-uniformities in the InGaN alloy on the emission and absorption spectra of InGaN bulk and quantum wells, and on the emission efficiency. We show, that some experimental quantities like the width of the spontaneous emission spectrum and the temperature dependency of the radiative recombination parameter can be well reproduced only when small deviations from a uniform random alloy are considered.

The effect of AlGaN interlayer (IL) composition in yellow-emitting InGaN/AlGaN/GaN multiple quantum wells (MQWs) is investigated. The IL-MQWs consist of 5 periods of In(x)Ga(1-x)N/Al(y)Ga(1-y)N/GaN MQWs emitting at 560nm with x~0.22, 3.3nm thick InGaN, and 10nm thick GaN. The Al(y)Ga(1-y)N interlayer has a thickness of 1.3nm and y is varied from 0 to 0.58. Reciprocal space maps about the (20-25) reflection, power dependent photoluminescence (PL) and differential carrier lifetime measurements are performed to determine the optimum AlGaN composition. At AlGaN interlayer composition of y~0.26-0.33 the MQW has the lowest defect recombination rate, resulting in the highest PL intensity and overall efficiency.

Night traffic and outdoor environment of night-time are familiar accident scenarios in our daily lives. To ensure the safety at night, use the correct lighting design to assist human mesopic vision is essential. However, most white LED spectra design was not born for such applications. Thus, to maximize mesopic luminance and 3D color gamut volume simultaneously, we optimize trichromatic white LED spectra by modified MOVE-model and a mesopic color appearance model. Our results indicated that SPD significantly influences the predicted mesopic luminance and 3D color gamut. Finally, 24 optimal trichromatic white LED spectra were well-derived for enhancing visual performance.

White light solid-state lighting (SSL) is conventionally based on light-emitting diodes (LEDs). Lately, laser diodes (LDs) have been proposed as a replacement due to their higher device efficiencies; however, laser radiation and eye-safety are always a concern. Superluminescent diodes (SLDs) bring together low coherency and high power, high efficiency and low speckle density, offering an alternative to both LEDs and LDs. Our work compares LED, LD and SLD, and demonstrates high-speed visible light communications and high-quality white light based on c-plane InGaN SLD, constituting a viable innovation for the lighting industry and for the adoption of blue SLD for commercial applications.

LED lighting penetration has risen significantly over the last few years. However, LED system reliability still remains a concern. A U.S. DOE report stated that most LED system failures were due to driver failure. Past studies revealed that the aluminum electrolytic capacitor (AEC) and the metal oxide semiconductor field effect transistor (MOSFET) are two driver components with the highest failure rates. This paper focuses on MOSFET failure analysis. Several MOSFETs were subjected to aging and the relevant output parameters were measured and analyzed to determine end-of-life criterion. An accelerated test method for LED driver failure based on MOSFET is proposed.

Solid-state lighting has rapidly been replacing traditional lighting due to its promise in meeting energy savings requirements. An edge-lit LED light fixture has the potential for high efficacy and long lifetime. In such fixtures, efficacy, distribution, and uniformity are the three main criteria often discussed. Only a few studies have analyzed optics to deliver an optimized beam for light fixtures. In this study, the light coupling and the light extraction efficiencies were optimized by tailoring the surfaces of the light guide. The results provide guidance for optical designers to consider when developing thin profile LED luminaires with the desired lighting properties.

LED A-lamps are used in many types of lighting fixtures; however, these lamps can experience different thermal environments and on-off switching, resulting in system life that varies in different applications. A recent study showed that on-off switching negatively affected lifetime and solder joint failure was the main reason. Although several models for solder joint fatigue failure exist, the Engelmaier model is the most commonly used in electronics industry standards. The study presented here showed that the Engelmaier model predicted the A-lamp cycles to failure with a maximum prediction error of 13%. This paper describers the test procedure, results, and Engelmaier model prediction methods.

AlGaN is a promising material for visible-blind ultraviolet (UV) photodetectors (PDs) owing to its wide and direct energy bandgap, high mechanical and chemical stability, and the ability to cover almost entire UV region from UVA to UVC by tuning the Al mole fraction from 0 to 1. Metal–semiconductor–metal (MSM) PDs offer substantial advantages over typical pn-type PDs such as fabrication simplicity, low dark current, and high speed operation. However, considering that the low transparency of conventional metal electrodes in the UV region limits the efficiency of MSM UV PDs, highly transparent electrodes such as graphene and its derivatives have great potential for further improvement of such devices. In this study, we fabricated AlGaN MSM UV PDs having two back-to-back reduced graphene oxide (rGO) Schottky electrodes.

Cell cultures are still predominantly determined by end-point investigation, due to the required incubation conditions. Therefore, the demand for observation of proliferation and differentiation kinetics, which contributes to the outcome of the cultivation, creates the need for an integrated microscopy solution capable of continuous imaging. In this work, a miniaturized lensless microscope based on LED technology was used to bridge the gap between sophisticated microscopy, bio-system integration, and real-time imaging, allowing the observation of growth and proliferation in organic samples. The capability of the device was demonstrated on living cells, under long-term measurement conditions, and in combination with microfluidic systems.

Semiconducting iron disilicide (β-FeSi2) has attracted much attention over the past ten years as one of the promising materials for fabricating infrared optoelectronic devices. It emits light of about 1.54 μm suitable for silica optical fiber communications. A clear PL spectrum from β-FeSi2 film was achieved by optimizing growth temperature in metal-organic chemical vapor deposition (MOCVD) method. A systematic band gap shift depending on the lattice deformation was observed in the β-FeSi2 epitaxial films. These results revealed that the band-gap energy was modulated systematically by the lattice deformation, which suggests a possibility of band gap engineering of β-FeSi2 epitaxial films.

High-resolution vehicle headlamps represent a future-oriented technology that can be used to increase traffic safety and driving comfort. By increasing the resolution of LED arrays, the challenges in designing an optical system for high-resolution headlamps rise. High efficiencies and contrasts call for small, accurate lens geometries and negligibly scattered light effects. Due to limited installation space and manufacturing tolerances, compromises have to be made. In this paper, design challenges and concepts to implement micro pixel LEDs in high-resolution headlamps, as well as the controllability of scattered light effects are discussed.

Silver sintered pastes offer a robust lead-free alternative to solder pastes increasing the lifetime of the device and enabling a higher heat dissipation. Due to the design of UV LEDs, they have to be connected to a heat spreading submount by flip chip joining. Silver sinter paste, which is adapted to the UV LED contact system, can be an alternative flip chip joining material compared to gold studs or solder. In order to evaluate different joining methods, UV LED devices were assembled by thermal compression bonding, diffusion bonding, soldering and sintering and compared according to, thermal resistivity, optical-electrical and mechanical behavior and reliability issues.

The quantum efficiency of deep UV LEDs is very small. There are a number of simulations that predict the thermal resistance. Two electrical methods for indirect determination of thermal resistance are presented. First the junction temperature is determined by the forward voltage using a constant current source. By means of a suitable equivalent electrical circuit model, the thermal resistances can be extracted. Second the frequency-dependent modulation capability of LEDs serves as the basis for the comparative measurement of the thermal resistance. Both methods are compared and the extracted data is translated into physical parameters of the LED chip.

The abundance of LED lighting fixtures has resulted in price erosion, forcing manufacturers to look for lower cost manufacturing. 3-D printing holds promise for making lower cost custom lighting fixtures. The objective of this study was to understand how short-term and long-term optical properties are affected when using 3-D printed optical components. Transmissive and reflective optical elements were printed and aged at higher ambient temperatures and their corresponding spectral transmission and the changes over time were measured and analyzed as a function of print parameters. The details of the printed components, test procedure, and results are described in this paper.

In this work, for the first time we provide experimental evidence that avalanche generation can take place in state-of-the-art InGaN-based blue LEDs. We measured the current-voltage and electroluminescence curves of the devices while pulsing them with increasing reverse voltages. We investigated a wide span of temperatures (from cryogenic to room temperature) in order to verify that the increase in leakage current detected below -80 V is related to avalanche generation (positive temperature-coefficient). Numerical simulations show that in this bias condition the band-to-band tunneling barrier thickness is low, leading to the possible injection of highly- energetic electrons from the p-side to the n-side that can start the avalanche process.

Advanced multi-channel illuminants consist of four or more strategically differentiated non-white LED illuminants. When simultaneously combined they can exhibit exceptional color fidelity, stability, efficacy, die area utilization, and more in contrast to systems of PC-white LEDs. They represent a fundamental forward-looking path in illumination – capable of fully addressing the limits of efficacy and spectral dynamics of human factors (temporal/circadian stimulus, color, intensity), imaging/sensors, and horticulture.

Traditional illumination systems uses various lamps selected based on certain requirements of the applications. One common issue is the trade-off between output brightness and lamp lifetime. LEDs with long lifetimes have been used in many applications. This paper describes a multi-colored 4-LED and 5-LED illumination system with individually controlled red, green, and blue outputs combined together with the etendue of a single LED, having enhanced green and red output brightness with supplementary excitation of the phosphor based green and red LEDs from additional blue LEDs increasing the overall output of the system. Computer modeling and experimental results will be presented.

To meet the demand of high-power light source for solid-state lighting (SSL) applications, we demonstrated GaN laser diode based white light system as a high-brightness and droop-free light source with minimized emitting surface. Our compact laser white light source shows a cool white light with color rendering index (CRI) as high as 84. A single unit delivers > 600 lm has been achieved. Our study suggests the laser lighting system being the competitor for high intensity white light sources.

“In seeing the word, what we do see is the light”. That’s why, to improve people living comfort and wellbeing, CoeLux® has tackled the very physical re-construction of the same light of the outdoor: to re-create the experience of an infinitely wide living space, no matter how small is hour home, office, car, etc. The goal is attained by a careful reconstruction of both the sun and sky light, their combined effect being essential for the perception of distances, volumes and shapes.

Electronic illumination systems are now available with multiple independently controllable LEDs of different spectral power distribution (SPD). These independent SPD can be combined in the proper proportions to replicate a target SPD. Generally at least four channels and sometimes eight or more channels are needed for a sufficiently broad tuning range. There are multiple optimization goals that may be of interest in defining the synthesized SPD. One application of these systems is to replicate the time-varying SPD of daylight towards a healthier and more enjoyable indoor illuminated environment. This talk will explore the general architecture of the systems, the algorithms for synthesizing an SPD, summary information of daylight recordings, and a brief demonstration of a light player.

Over the past 60 years, advances in color quality metrics have gone hand-in-hand with advances in light source technology. The situation remains the same today: LED technology prompted the development of new measures of color rendition, which then led to new research that will inform the next generation of light sources. After reviewing the continued development of IES TM-30, this presentation will review recent research to identify important target spectral characteristics for high-quality, high-efficiency lighting.

LED lighting systems using Power-over-Ethernet (PoE) technology have been introduced to the lighting market in recent years as a network-connected lighting solution. The objective of this study was to characterize a PoE-based LED lighting system and identify the power losses at the different parts of the system. Based on the findings, we developed a methodology for characterizing the electrical efficiency of a PoE-based lighting system and then characterized and compared several commercially available PoE systems. The study also investigated the discrepancy between the measured and reported energy use of the system components.

Spectrally-tunable solutions make it possible to shape the light spectral power distribution (SPD) according to the needs of different market segments. Unfortunately, there is a lack of spectral tools that are available in the market for lighting designers. Can thousands of SPDs be filtered and sorted in real time depending on the intended application (i.e. Human Centric Lighting, horticulture, museum lighting, etc.)? In this work, we present a mathematical tool and a physical multi-channel LED engine to optimize for different parameters, i.e. flux, illuminance, efficacy, CRI-Ri, TM30-15-Ri, Damage Potential, melanopic flux, SP/MP ratios, CLA/CS, etc. in incredibly short computation times.