This PDF file contains the front matter associated with SPIE Proceedings Volume 6910, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The ThinGaN^® technology of OSRAM Opto semiconductors enables high power LEDs with wall plug efficiencies of currently up to 50%, enabling efficacies of > 100lm/W for white and green LEDs. The good scalability of the technology enables devices which deliver high luminous flux. The future limitations regarding efficacy of white LED can be estimated to be 150lm/W for high color rendering. Besides efficiency long term stability and high temperature capability are requirements for market adoption

The internal quantum efficiency (IQE) of commercial ultra high brightness AlGaInP red LED has already reached 90% or higher but the light extraction efficiency was only about 30% to 50%. Through the improvement of surface texturing structure by nano-imprint technology and current spreading by using narrow width ohmic contact metal line, the light extraction efficiency of AlGaInP red LED was significantly improved up to 60%. In AlGaInN LED, the thermal resistance of the LED chip can be reduced by thinning down or totally removing the sapphire substrate and then replacing it by high thermal conductivity materials. Therefore, the performances of high power AlGaInN LED chips were improved in high current density operation condition.

The optical properties of OLEDs can be tailored by optimization of the layer stack and by implementation of micro- and/or nano-optical structures. But the effect of changing the OLED configuration on the device performance crucially depends on the optical properties of the emissive layer. The aim of this contribution is twofold. First, we will propose and demonstrate a general and reliable method to determine the intrinsic optical emitter properties via simple optical characterization and corresponding reverse simulations. Second, the influence of the emitter properties on homogeneous OLEDs as well as on OLEDs with micro/nano-optical structures is discussed.

Phosphor down-conversion of blue organic light-emitting diodes (OLEDs) is one approach to generate white light, which offers the possibility of easy color tuning, a simple device architecture and color stability over lifetime. In this article previous work on down-conversion devices in the field of organic solid state lighting is briefly reviewed. Further, bottom emitting down-conversion OLEDs are studied from an optical point of view. Therefore the physical processes occurring in the down-conversion layer are translated into a model which is implemented in a ray tracing simulation. By comparing its predictions to experimental results the model is confirmed. For the experiments a blue-emitting polymer OLED (PLED) panel optically coupled to a series of down-conversion layers is used. Based on results obtained from ray tracing simulation some of the implications of the model for the performance of down-conversion OLEDs are discussed. In particular it is analysed how the effective reflectance of the underlying blue OLED and the particle size distribution of the phosphor powder embedded in the matrix of the down-conversion layer influence extraction efficiency.

New light-emitting PCPP derivatives, poly(4,4-bis{4-[(2-ethylhexyl)oxy]phenyl}-4H-cyclopenta[def]phen- anthrene) (BEHP-PCPP), with stabilized blue emission is reported. The OLED with the configuration of ITO/PEDOT:PSS/BEHPPCPP/ Ca/Al generates EL emission with maximum peak at 430 nm, low turn-on voltage (9V), and CIE coordinates (x = 0.19, y = 0.15) for the blue color without any filtering. The maximum brightness of the OLEDs using BEHP-PCPP was 1034 cd/m² at 15 V. The maximum luminescence efficiency of the polymer LEDs with BEHP-PCPP was 0.21 cd/A at 617 mA/cm².

Light emitting diodes (LEDs) are being utilized as the light source in increasingly complex and sophisticated products, including flat panel displays, surgical lamps and even digital projectors. These applications place extreme demands on LED performance, which, for both the developer and manufacturer, translate into the need to precisely characterize and control source output, specifically color and luminous intensity distribution characteristics. Unfortunately, the traditional methods for performing luminous intensity and colorimetric measurements of LEDs suffer from several significant drawbacks. In particular, spot photometers and radiometers only sample a very limited amount of source output and operate very slowly. The latter factor can be an important consideration, even in research settings, because LED output is often not stable over time, especially during warm-up or in the presence of temperature or input power fluctuations. Thus, a long data acquisition period can make an instrument report spatial output variations that don't really exist. Now, new instrumentation based on the Imaging Sphere enables rapid, high spatial resolution measurement of LED color and luminous intensity over an entire hemisphere. This paper reviews the parameters typically utilized to characterize LEDs, explores Imaging Sphere operation, and compares the results of Imaging Sphere measurements with highly accurate reference data from a goniophotometer.

Violet and blue Laser diodes, as well as highly efficient high-power Light Emitting Diodes (including any UV emitters) can be constructed using low-dislocation-density freestanding GaN substrates, either produced as thick HVPE layers on foreign substrates, or using direct methods of crystallization as ammonothermal one or high pressure growth from the nitrogen solution in gallium. This paper shows some of the most most important issues concerning application of such substrates. The first issue is the choice of the substrate thickness influencing the accommodation of strain, cracking and bowing of the samples. In this point, a new way of prestressing the substrate by lateral patterning will be presented. The second issue is the surface preparation either by mechanical polishing and reactive ion etching, or mechano-chemical polishing, in particular, a distribution of defects revealed by chemical etching will be discussed. Finally, the problem of substrate misorientation influencing the further morphology and indium incorporation into InGaN quantum wells will be shown. For higher misorientation of the substrates, the incorporation of indium decreases , but at the same time, the fluctuations of indium increase giving blue-shifted, weaker and broader photoluminescence peaks.

The availability of GaN substrates is crucial for GaN-based laser diodes. Also high performance LEDs ask for high quality substrates. Methods for growth of bulk GaN are reviewed with a focus on hydride vapour phase epitaxy (HVPE), which currently is the method used for the production of GaN substrates. Also the ammonothermal approach is briefly discussed. Both approaches still have to overcome limitations before mass-production at affordable prices is feasible. These limitations are related to the maximum growth rate yielding high quality material as well as the boule length that can be achieved together with high material quality.

We demonstrated and analyzed 480-nm emitting III-Nitride LEDs using SiO₂/polystyrene (PS) microlens arrays, deposited via rapid-convective-deposition. Output power of MOCVD-grown InGaN QW LEDs with SiO₂/PS microlens exhibited improvement of 219%. Numerical simulation of the light extraction efficiency optimization of III-Nitride LEDs with SiO₂/PS microlens was carried out using Monte Carlo ray tracing including 3D self-consistent photon-carrier interaction. The light extraction efficiency of the LEDs with microlens array is optimized for the PS layer thickness and the SiO₂ microspheres diameter. The simulations show good agreement with experiments, indicating the use of SiO₂/PS microlens leads to increased photon escape cone.

We have demonstrated an improvement of light extraction from GaN based flip-chip LEDs by patterning encapsulant. Two dimensional (2D) micron-scale patterns of encapsulant were realized by using imprint technique of thermosetting polymer. This approach has several advantages such as technical simplification, low cost and freedom of material choice. In this work, we fabricated 2D micron-scale patterns with the triangular or sinusoidal profiles on the polymer encapsulated GaN-based flip-chip LEDs. The enhancement factors of light extraction of GaN LEDs with the patterned encapsulant comparing to the flat encapsulated LEDs are about 32% and 47% corresponding to the triangular and sinusoidal profiles, respectively. To evaluate the concept of a diffraction grating in enhancement of light extraction, we performed a simulation of diffraction based on simplified one-dimensional (1D) rigorous coupled wave analysis (RCWA). The calculation reveals that the grating of sinusoidal profile has greater transmittance than that of triangular profile which is in the same trend with the experimental results. These results provide a guideline for improvement of the LED light extraction.

Light emitting devices (LEDs) based on colloidal semiconductor nanocrystals represent a matter of technological interest for the development of flat panel display and lighting systems. The appealing features of these materials are the high fluorescence efficiency, narrow ban edge emission, potential chemical stability, and tunable light emission across the visible spectrum. These characteristics open the way to a new class of hybrid devices in which the flexible technology of organic LEDs can be combined with the long operating lifetime of inorganic semiconductor devices. In particular over the last few years several hybrid device structures based on colloidal semiconductor quantum dots (QDs) and organic material have been reported. In this paper we report on recent development in the fabrication of QDLEDs and in particular in white hybrid LEDs.

We demonstrate a manufacturing approach of nanostructures on the large surface area of GaN-based LED chip to improve the light extraction efficiency. We prepared the nanoporous anodic aluminum oxide (AAO) template on an aluminum foil by the conventional two-step anodization. Using the AAO template as etching mask, we successfully transferred the nanoporous structures to the surfaces of GaN-based LEDs by inductively coupled plasma dry etching. About a quarter of two-inch GaN-based LED chip was patterned by the nanostructures. The pore spacing was modulated from 100 nm to 400 nm. The improvement of light extraction efficiency of the device was achieved. A light output power enhancement of 42% was obtained from the p-side surface nanopatterned LEDs compared to the conventional LEDs on the same wafer at 20 mA. This approach offers a potential technique of nanostructures fabrication on GaNbased LEDs with the advantages of large area, rapid process and low cost.

We report on submicron-thick microcavity light emitting diodes (MCLEDs) emitting at the wavelengths of 415 nm ~ 460 nm. These devices were fabricated by flip-chip-bonding, laser lift-off, and thinning processes. Growth of a highquality Al_xGa_1-xN interlayer and etch selectivity between N-face GaN and Al_xGa_1-xN allowed high-precision control of microcavity thickness, resulting in controlled microcavity effects. Single Fabry-Pérot modes confined in 2λ ~ 2.5λ-thick MCLEDs gave rise to characteristic angular emission, in contrast to a Lambertian emission. High current operation (~100 mA) showed robustness of these thin devices with promising the possibility of high-brightness application. We will discuss design and processing issues regarding photonic-crystal integration towards higher improvements in light extraction efficiency.

Sufficient lighting is sometimes required when surgeons watch the mediastinum through the 7x7cm thoracic window in video-assisted thoracoscopic (VATS) lobectomy. It is thus important to develop the "ultimately localized solid-statelighting" because the distance between the window and the surface of the lung is as short as 4-5 cm. Our new idea was to place the module composed of red, green and blue light emitting diodes (RGB LEDs) at the tip of the retractor. Compared to a conventional endoscopic lighting consisting of halogen lamp, this method has lead to the bright and shadowless illumination within the entire thoracic cavity since the white RGB LEDs are emitted unidirectionally from the cylinder-shaped camera component, moving the shadows from the surgical instruments to the side of the incision. It also should be noted that we found an effective principle for controlling the color rendering of each biomaterial through the synthesis of LED lighting spectra, by which the visual performance of surgeons can be coordinated. Therefore, we believe that "medical RGB LEDs" will contribute to the safe operation, and will be developed to a standard lighting system in clinical settings with bright surgical fields in the near future.

The unique properties of LEDs offer significant advantages in terms of lifetime, intensity and color control, response time and efficiency, all of which are very important for illumination in machine vision applications. However, there are some drawbacks of LEDs, such as the high thermal dependency and temporal degradation of the intensity and color. Dealing with these drawbacks requires complex LED drivers, which are able to compensate for the abovementioned changes in the intensity and color, thereby maintaining higher stability over a wide range of ambient temperature throughout the lifetime of a LED light source. Moreover, state-of-the-art machine vision systems usually consist of a large number of independent LED light sources that enable real-time switching between different illumination setups at frequencies of up to 100 kHz. In this paper, we discuss the concepts of smart LED drivers with the emphasis on the flexibility and applicability. All the most important characteristics are being considered and discussed in detail: the accurate generation of high frequency waveforms, the efficiency of the current driver, thermal and temporal stabilization of the LED intensity and color, communication with a camera and personal computer or embedded system, and practicalities of implementing a large number of independent drive channels. Finally, a practical solution addressing all of the abovementioned issues is proposed with the aim of providing a flexible and highly stable smart LED light source driver for state-of-the-art machine vision systems.

The high energy efficiency and radiant flux of high-power LED devices has lead to many new applications of LED lighting. Within the more production oriented applied plant research, there is a need for illumination systems that ensures a high irradiance, spectral control and homogeneous illumination of a large plant canopy to ensure reproducible results over long term measurements. A new high power LED illumination system is presented. It has been designed and developed for illumination of a plant canopy area of 60 x 80 cm² in a climate chamber where photosynthesis of the whole canopy can be measured. The LED system extends the precise control of the chamber climate with computer control and long term stability of the irradiance and spectral composition of the illumination. High-power red and blue (at 455 and 639 nm) LED devices have been chosen that coincides with the absorption peaks of chlorophyll. The illumination system allows for a maximum irradiance of 6.3 W/cm² corresponding to a photosynthetic photon flux density (PPFD) of 300 μmol m^-2 s^-1. The spectral composition of the light given by the ratio of blue photons compared to the total number of red and blue photons can be adjusted from 0-40 % keeping the irradiance at a constant level. Spectroradiometric 2D grid measurement at the plant top level shows homogeneity of ± 5% of the irradiance and ± 5% of the spectral distribution, over almost the entire canopy area. Initial experiments carried out on Chrysanthemum plants showing the dependence of the photosynthesis on blue light fraction is presented and discussed.

LEDs can be used as light emitters as well as detectors. It is known that like any PN junction, an LED too can be modeled as a capacitor in parallel with a light dependent current source ^[4]. 'ePaper' exploits this property of LEDs. 'ePaper' is an LED based graphic tablet which allows a user to write or sketch on an inexpensive hand held device. Multiple pages can be saved on the device which can be scrolled through and uploaded to a computer as bitmaps. ePaper is designed to be scalable to any desired dimension.

There is a high demand for compact low-cost ozone (O₃) sensors. It has been shown that indium oxide (In₂O₃) thin films grown by metal-organic vapor-phase epitaxy (MOVPE) act as an O3 sensitive material, which can be activated at roomtemperature by ultraviolet (UV) light. In the present work we integrated the In₂O₃ sensing thin film and an (AlGaIn)N based near-UV LED back-to-back on a single sensor chip. The integrated In₂O₃ film-LED sensor was exposed to varying ozone concentrations ranging from 38 ppb to 726 ppb and found to be sensitive to even the lowest O₃ concentration.

After an introduction of the basic concepts for solid-state-lighting, i.e. multi-chip LEDs and phosphor-conversion LEDs based on blue or near-UV pump LEDs, white LED phosphors are discussed regarding their match to different application requirements. Since the US Energy Star requirements have set first 'standards' for LED lighting, we evaluate different phosphor solutions for white LEDs mainly regarding these requirements. Efficient daylight LED for outdoor applications can be realized using yellow orthosilicates or garnets. Looking at cool white or even warm white LEDs with CRI 75+ blends of garnets and red nitrides are first choice. Solutions based on garnets and nitrides are superior, where CRI and/or color stability is important. Finally, the strong and package-dependent effect of particle size and scattering on color and efficiency is discussed.

The high-power phosphor-based white-light-emitting diodes (LEDs) after thermal aging at 150°C and 500 hours are studied experimentally. The white-light LEDs formed by three combinations of different thicknesses and concentrations of the silicone YAG phosphor are 1 mm and 5.48%, 2mm and 3.2%, 3mm and 2.4%, respectively. The results showed that the lumen loss, chromaticity (CIE) shift, and spectrum intensity reduction in yellow YAG phosphor of the highpower white-light LEDs increased as the silicone YAG phosphor concentration increased. These were due to that the transmittance loss and the refractive index variation of the silicone YAG phosphor increased as the aging time increased and resulted in lower emission efficiency of the high-power white-light LEDs. However, the lumen loss and CIE shift did not significantly depend on the thickness of the silicone YAG phosphor. The likely cause for the transmittance reduction and refractive index variation increased is that the thermal effect increased after thermal aging. As a result, the key of high-power phosphor-based white-light LEDs module package related degradation mode under thermal aging was identified as the decay of the silicone YAG phosphor, evidenced by secondary-ion mass spectroscopy (SIMS) analyses. This study clearly indicates that in order to maintain luminous power and minimize color shift of the highpower white-light LEDs modules, a lower concentration of the YAG phosphor for use in packaging of the phosphorbased white-light LEDs modules is essential.

Staggered InGaN quantum wells (QW) grown by metalorganic chemical vapor deposition was demonstrated as improved active region for visible light emitters. Fermi's Golden Rule indicates that InGaN QW with step-function like In distribution leads to significantly improved radiative recombination rate and optical gain due to increased electronhole wavefunction overlap, in comparison to that of conventional InGaN QW. Spontaneous emission spectra of both conventional and staggered InGaN QW were calculated based on energy dispersion and transition matrix element obtained by 6-band k•p formalism for wurtzite semiconductor, taking into account valence-band-states mixing, strain effects, and polarization-induced electric fields. The calculated spectra for the staggered InGaN QW showed enhancement of radiative recombination rate, which is in good agreement with photoluminescence and cathodoluminescence measurements at emission wavelength regime of 425-nm and 500-nm. Experimental results of light emitting diode (LED) structures at 45-nm utilizing staggered InGaN QW show improvement in output power much higher than what is predicted theoretically. Reduction in non-radiative recombination rate due to improved materials quality, in addition to the enhancement in radiative recombination rate in the staggered InGaN QW could presumably be the reason behind this significant output power improvement.

Four B-implanted p-n junction silicon light-emitting diodes were designed and simulated under identical fabrication process and recombination mechanisms by using Silvaco simulators. In the simulations, the implant energy and dose and the post-implant anneal temperature were varied to compare the designs in terms of band-to-band radiative recombination rates and locations. It was found that a pillar design wrapped with p-n junction has the greatest radiative recombination rate. Regardless of the designs, the radiative recombination rate is always higher in the B-implanted p⁺ region than in the n^- substrate. When the implant energy and dose are kept constant, there exists a peak in maximum radiative recombination rate when the anneal temperature increases from 700 to 1100 °C, and the temperature at peak increases while the implant dose increases. When the anneal temperature is kept constant, the radiative recombination rate always increases with implant dose but saturates at a dose when maximum solubility of dopants is reached at the temperature; however, the radiative recombination rate does not change significantly with implant energy. It was found that the effects of implant parameters and anneal conditions on BB radiative recombination rate could be correlated with active dopant concentration. In order to achieve high-efficiency silicon p-n junction diodes, implant parameters and anneal conditions must be optimized to maximize the active dopant concentration in the p⁺ region along with the spatial confinement of extended defects.

The performance requirements for packaging ultra high-brightness LEDs are extremely demanding. These include high continuous use temperatures and light fluxes. Polymer encapsulants play a critical role in the extraction of light, as a host medium for the phosphors to convert blue to white light, and as capping lenses. Encapsulants must also meet critical requirements for viscosity, modulus, and optical transmission under varying environmental conditions, while having a high refractive index to maximize device efficiency. We describe the development of robust one-pot encapsulants having refractive indices of 1.57 and greater than 1.6. These encapsulants are stable at 200 °C for time periods greater than 4 weeks.

Heat dissipation, thermal stresses and cost are key light-emitting diode (LED) packaging issues. Heat dissipation limits power levels. Thermal stresses affect performance and reliability. Copper, aluminum and conventional polymeric printed circuit boards (PCBs) have high coefficients of thermal expansion, which can cause high thermal stresses. Most traditional low-coefficient-of-thermal-expansion (CTE) materials like tungsten/copper, which date from the mid 20th century, have thermal conductivities that are no better than those of aluminum alloys, about 200 W/m-K. An OIDA LED workshop cited a need for better thermal materials. There are an increasing number of low-CTE materials with thermal conductivities ranging between that of copper (400 W/m-K) and 1700 W/m-K, and many other low-CTE materials with lower thermal conductivities. Some of these materials are low cost. Others have the potential to be low cost in high-volume production. High-thermal-conductivity materials enable higher power levels, potentially reducing the number of required LEDs. Advanced thermal materials can constrain PCB CTE and greatly increase thermal conductivity. This paper reviews traditional packaging materials and advanced thermal management materials. The latter provide the packaging engineer with a greater range of options than in the past. Topics include properties, status, applications, cost, using advanced materials to fix manufacturing problems, and future directions, including composites reinforced with carbon nanotubes and other thermally conductive materials.

Key market requirements for white LEDs, especially in the general lighting and automotive headlamp segments call for improved concepts and performance of white LEDs based on phosphor conversion. Major challenges are small emission areas, highest possible intensities, long-term color stability, and spatial homogeneity of color coordinates. On the other hand, the increasingly high radiation power of the blue LEDs poses problems for all involved materials. Various thick film coating technologies are widely used for applying the color conversion layer to the semiconductor chip. We present novel concepts based on Silicate phosphors with high performance in terms of spatial homogeneity of the emission and variability of the color temperature. Numerical calculation of the optical properties with the help of state-of-the-art simulation tools was used as a basis for the practical optimization of the layer geometries.

New fluorin-containing electroluminescent polymers in vinylene units, poly(2-dimethyldodecylsilyl-p-phenylenedifluorovinylene) (DMDS-PPDFV), have been synthesized by GILCH polymerization. This polymer has been used as the electroluminescent layers in light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). DMDS-PPDFV shows PL around λ_max = 455 nm (exciting wavelength, 365 nm) and green EL around λ_max =489nm. Attachment of two the fluoro groups were introduced to poly(2-dimethydodecylsilyl-1,4-phenylenevinylene) (DMDS-PPV) to give DMDSPPDFV in an attempt to increase the electron affinity of the parent polymer.

New electroluminescent polymer with tetrakis-alkoxy group, poly[2,3,5,6-tetrakis(2-ethylhexyloxy)-1,4- phenylenevinylene] (TEH-PPV), has been synthesized by the Gilch polymerization. TEH-PPV with tetrakisethylhexyloxy groups in phenylene unit can get shorter conjugation length than MEH-PPV, and had more blue shifted absorption and emission peaks due to steric hindrance. Tetrakis-ethylhexyloxy groups induced very conjugated backbone is twisted. And, they can enhance the internal efficiency of the conjugated polymer as emissive layer in PLED because of the restraint of inter-chain interaction by the avoidance of close packing to give decent device performance.