This PDF file contains the front matter associated with SPIE Proceedings volume 7422, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Although Si and Mg impurities are essential elements for n and p type GaN, unintentional incorporation into InGaN-multiple quantum wells (MQWs) seriously affects the optical property of LEDs. Si doping in MQWs obstructs the hole carrier transport and induces the dead quantum wells (QWs) of MQWs. Also, Mg impurity diffusion from p- GaN into MQWs degrades the radiative recombination rate of the QWs placed near Mg doped p-GaN layer. In this paper, the effects of Si and Mg impurities on the optical property were systematically investigated.

The green spectral region provides a formidable challenge for energy efficient light emitting diodes. In metal organic vapor phase epitaxy we developed GaInN/GaN quantum well material suitable for 500 - 580 nm LEDs by rigorous defect reduction and thrive for alloy uniformity. We achieve best results in homoepitaxy on polar c-plane, and non-polar a-plane and m-plane bulk GaN. By the choice of crystal orientation, the dipole of piezoelectric polarization in the quantum wells can be optimized for highest diode efficiency. We report progress towards the goal of reduced efficiency droop at longer wavelengths.

Color Rendering Index, CRI, is a widely used metric to provide a means of determining light quality using measured color shift from a reference source. CRI has several known deficiencies however and there is active research in new metrics. As part of this research, a new tool has been developed to create a wide variety of spectral power distributions, SPD. The tool is called a Spectrally Tunable Light Source, STLS. We detail objectives and the detailed design of an STLS system involving thousands of high-power LEDs across the visible spectrum.

Alternating-current (AC) driven high-power light-emitting diodes (LEDs) have become available and introduced into solid-state lighting (SSL) products. AC LEDs operate directly from a mains supply with no need of drivers, and thus can simplify the design of SSL product and potentially increase product's reliability and lifetime. Similar to direct-current (DC) LEDs the optical and electrical properties of AC LEDs are strongly dependent on the LED junction temperature. In addition, the instantaneous junction temperature of an AC LED changes rapidly within an AC power cycle. Accurate measurement of AC high-power LEDs is required for quality control and product qualifications such as the US Energy Star. We have developed a simple, robust method for measurement of high-power AC LEDs at any specified junction temperature under a normal AC operating condition. An active heat sink is used for setting and controlling the junction temperature of the test AC LED. By using this measurement technique, the measurement of an AC LED also obtains the thermal resistance between the LED junction and the LED heat sink.

Although light-emitting diodes (LEDs) have the potential for long life, LED luminaires may experience a much shorter life for the system as a whole because of the driver. Past studies show that the electrolytic capacitor used in switch-mode power supplies often has the shortest lifetime, and thus determines the electronic driver lifetime. This study demonstrated an accelerated life test method for LED drivers that use electrolytic capacitors at the output stage by monitoring the output current ripple trends at different elevated operating temperatures.

Near ultraviolet (n-UV) LED-based white light source (LS) can provide the excellent illuminant properties that show high-luminous efficacy (Le>80 lm/W) of radiation and high-color rendering index (CRI or Ra>99). Recent progress and future advantages of the n-UV white LED technology on the basis of our direct flip-chip bonding and stacked multi-layer structure methods will be described. Particularly, the fabrication process, and electrical and illuminant properties in the low-correlated color temperature (CCT or Tc~3452K) white LED with a high-luminous flux (~500 lm/PKG) are discussed, and its lighting and medical applications such as ecological street lighting and gastrointestinal digestive endoscope will be introduced. Furthermore, a color tunable white LS which is composed of multi-phosphor conversion LEDs and its characterization are described. Differences on the quality of light between the n-UV white LED and the conventional blue-YAG white LED will be clarified.

Phosphors in LED packages can experience much higher temperatures (>100°C) and light fluxes (>10 W/cm²) versus traditional phosphors in fluorescent lighting. These conditions place stringent restrictions on LED phosphor selections and requires, to some extent, an understanding of the potential quenching mechanisms that occur within LED packages. In this report, we discuss flux-based and temperature-based quenching of LED phosphors, the measurements used to analyze these quenching processes, and some of the basic mechanisms behind this. It is shown that flux-based quenching in LEDs can be reasonably anticipated through simple design parameters. However, while it is more difficult to a priori predict the thermal quenching of new phosphors and their modifications, it is possible to make initial conclusions about phosphor design through a combination of spectroscopic measurements and chemical inference. This is specifically demonstrated within the Ce³⁺-doped garnet family of phosphors, where there is significant flexibility to modify compositions, leading to initial relationships between composition, emission color, and high temperature quenching.

This paper reports an extensive analysis of the degradation of Phosphor-Converted Light-Emitting Diodes (pc-LEDs) submitted to accelerated stress tests. We describe the degradation modes of state-of-the-art white LEDs, and the dependence of the Time-To-Failure on the adopted stress conditions. The analysis was carried out on two different sets of commercially available low-power LEDs, stressed under different current (in the range 30-50 mA) and temperature (in the range 80-140 °C) levels for 1600 hours. We have carried out an extensive analysis of the thermal properties of the LEDs, and extrapolated the junction temperature of the devices under the different applied stress conditions. The results of this work indicate that stress can induce both a gradual and a catastrophic degradation of the LEDs. The failure modes detected during gradual degradation are a decrease in the luminous flux and the worsening of the chromatic properties of the LEDs. Experimental data indicate that the degradation kinetics can be strongly influenced by the stress temperature level, and do not significantly depend on the stress current level. On the basis of the results presented within this paper, gradual degradation can be ascribed to the worsening of the optical properties of the package and phosphors-encapsulant of the LEDs. Furthermore, we show that high stress conditions can also determine an increase in the thermal resistance of the samples: by means of X-Ray analysis, we demonstrate that this effect is due to the partial detachment of the LED-phosphors system from device package. Finally, we show that catastrophic degradation is mostly correlated to the shortening of the junction. This effect is due to the generation of parasitic conductive paths that can be identified by means of emission microscopy.

ZnO is a promising substrate for GaN growth due to a lattice match with In_.18Ga_.82N, similar thermal expansion coefficient, and its ability to be easily chemically etched, which results in improved light extraction. A transition layer of Al₂O₃ was also grown by ALD prior to MOCVD growth to prevent Zn diffusion, protect the ZnO substrate from H2 back etching, and promote high quality nitride growth. Thick InGaN layers (~200-300nm) were grown in this study on bare ZnO substrates and ALD/ZnO substrates. Various buffer layers were attempted, such as SLs of AlGaN/GaN, MQWs of InGaN/GaN, and LT-GaN. These results are significant as previous studies showed decomposition of the layer at InGaN thicknesses of 100nm or less. These layers allowed for the first LEDs to be grown on bare ZnO substrates. This study demonstrated that InGaN LEDs showed emission in optical measurements as well as a high IQE of ~60%. The data shows promise for LED structures on ZnO using InGaN as n- and p-type LED layers. Etching of the ZnO substrate also showed that removal of the substrate can be performed easily.

The challenge of growing GaN and its alloys, In1-xGaxN and Al1-xGaxN, is still formidable because of the lack of close lattice match, stacking order match, and similar thermal expansion coefficient substrates, the same as GaN-based optoelectronic materials. ZnO is the most promising optoelectronic materials in the next generation, with wide band gap of 3.3eV and exciton binding energy of 60meV. In addition, ZnO also has been considered as a substrate for epitaxial growth of III-Nitrides due to its close lattice and stacking order match. Our works cover the growth of n-type InGaN and GaN epitaxial layers on lattice-matched ZnO substrates by metal-organic chemical vapor deposition (MOCVD). Since MOCVD is the dominant growth technology for GaN-based materials and devices, there is a need to more fully explore this technique for ZnO substrates. However, the thermal stability of the ZnO substrate, out-diffusion of Zn from the ZnO into the GaN, and H2 back etching into the substrate can cause growth of poor quality GaN. We use a GaN buffer layer of about 40nm to avoid Zn/O diffusion. We can investigate the Zn/O diffusion in the InGaN epilayers by means of second ion mass spectroscopy (SIMS) depth profiles, and analyze the surface bonding of different elements by x-ray photoelectron spectroscopy (XPS), and investigate optical and structural characterization of InGaN epilayers on ZnO substrates by various angles spectroscopic ellipsometry (VASE). Finally, from the Raman scattering, Photoluminescence (PL) and Photoluminescence excitation (PLE) spectra, we can determine the qualities easily and prove that we have grown the InGaN on ZnO with a GaN buffer layer successfully.

In this work, an effective method for controlling light emission of light-emitting diodes(LEDs) is proposed to maintain the light-emission characteristics. Wholly, there are two physical concepts of LEDs unutilized in this controlled method. One concept is the forward voltage and the junction temperature of LEDs could be described as a simple and linear relationship according to electric-thermal properties of LEDs. Thus the behavior on the junction temperature of LEDs could be monitored by a voltmeter in real time. The other concept is modulating the heat energy accumulated inside LEDs' junction by a heat dissipation module in real time. Therefore, with these physics concepts of LEDs, the effective method for controlling light emission of LEDs is implemented well by an aid of the feedback control mechanism. The results show the performance on the light-emission characteristics could be controlled to keep as a steady state, including optical power, peak wavelength and chromaticity under the feedback control mechanism.

One key challenge with the the use of III-nitride materials in solid state lighting devices is the use on thermally and/or electrically insulating substrates. In order to transition the lift-off tehniques from laserbased processing to more benign chemical techniques, it is essential to realize the integration of chemical soluble layers into the LED-growth process. This work presents the comparison of physical and chemical vapor deposition techniques used in the growth of ZnO, one such possible isostructural buffer layer and a comparison of the materials properties of samples grown by low temperature chemical vapor deposition and pulsed laser deposition. The quality of the films was highly dependent on the growth conditions and substrate preparation. For room temperature depostion, amorphous ZnO films were observed, while completely oriented films were observed for 750°C growth. Pulsed chemical vapor deposition of the films at 175°C showed smoother polycrystalline films with c-axis texture. ZnO films were etched at room temperature demonstrating the suitability for chemical liftoff.

Device-quality GaN thin films have been grown on Si(111) substrates using an Al₂O₃ transition layer, and initial devices show performance similar to comparable devices on sapphire. X-ray diffraction rocking curve scans show a linewidth of 378 arcsec for the GaN (0002) reflection. Comparison of these layers to GaN layers grown on bare Si substrates shows a significant reduction in strain with the use of the Al₂O₃ transition layer. Raman spectroscopy measurements verify this reduction in strain, as shown by the shift of the GaN E₂(high) with variations in Al₂O₃ layer thickness. GaN-based devices were also grown and fabricated using this process. Devices on Si showed an IQE of ~32%, which is comparable to the ~37% observed for similar devices on sapphire. The devices on Si also showed better efficiency at high current densities compared to the devices on sapphire, despite the longer peak emission wavelength on Si, which may be due to a difference in thermal conductivity between Si and sapphire. A growth process has been developed for high-quality GaN on Si, and initial device results show that Si is a viable substrate technology for MOCVD growth of GaN-based devices.

Three blue emission multi-quantum well (MQW) light emitting diode (LED) samples with different indium composition and different amount of quantum wells were studied. From x-ray diffraction and transmission electron microscopy experimental measurements, the period thickness and indium composition of the sample have been obtained. The temperature dependent photoluminescence (PL) shows that the signal from InGaN/GaN samples was influenced by two kinds of factors. One is the band to band transition of InGaN; another is the localization effect caused by the non-uniformity of the In composition in In-rich samples. While the temperature increases, full width half maximum becomes larger, and the signal tends to shift to the red side. Through theoretical fitting on the temperature dependent PL data, the activation energies (Ea) of the InGaN multi-quantum well samples were obtained. Time-resolved photoluminescence (TRPL) results show that as the indium composition increases and the QW number increases, a longer decay time will get. From the results of photoluminescence excitation (PLE) experiment, a large Stokes shift (SS) was observed. The large Stokes shift can be attributed to the variation of indium composition or the quantum confined Stark effect (QCSE). Also, the Photoluminescence spectra exhibit weak blue peaks and the optical intensity is improved by increasing the number of wells.

On a short to medium term, energy efficient retrofit LED products can offer an attractive solution for traditional lamps replacement in existing fixtures. To comply with user expectations, LED retrofit lamps should not only have the same mechanical interface to fit (socket and shape), but also have the similar light effect as the lamps they replace. The decorative lighting segment shows the best conditions to meet these requirements on short term. In 2008, Philips Lighting Shanghai started with the development of an LED candle lamp for the replacement of a 15W Candle shape (B35 E14) incandescent bulb, which is used in e.g. chandeliers. In this decorative application the main objective is not to generate as much light as possible, but the application requires the lamp to have a comparable look and, primarily, the same light effect as the incandescent candle lamp. This effect can be described as sparkling light, and it has to be directed sufficiently downwards (i.e., in the direction of the base of the lamp). These requirements leave very limited room for optics, electronics, mechanics and thermal design to play with in the small outline of this lamp. The main voltage AC LED concept is chosen to save the space for driver electronics. However the size of the AC LED is relatively big, which makes the optical design challenging. Several optical solutions to achieve the required light effect, to improve the optical efficiency, and to simplify the system are discussed. A novel prismatic lens has been developed which is capable of transforming the Lambertian light emission from typical high power LEDs into a butter-fly intensity distribution with the desired sparkling light effect. Thanks to this lens no reflecting chamber is needed, which improves the optical efficiency up to 70%, while maintaining the compact feature of the original optics. Together with advanced driver solution and thermal solution, the resulting LED candle lamp operates at 230V, consumes 1.8W, and delivers about 55 lm at 3000K with the requested radiation pattern and sparkle effect. Some field tests were done with positive feedback.

Reduced maintenance cost due to the long life of light-emitting diodes (LEDs) has attracted the lighting community to this rapidly evolving lighting technology. A high LED junction temperature negatively affects the performance of LEDs. To realize the long-life potential of LEDs, proper thermal management is necessary. This paper describes a numerical and experimental investigation of thermal solutions for an LED recessed downlight under passive cooling. Different heat transfer mechanisms and their contributions for keeping the LED junction at lower temperatures also were analyzed.

Multi-national patents and applications data, based on filings in patent authorities worldwide, are used as a means to probe corporate and national R&D roles in the emerging LED and SSL industries. The data are counts of patents, applications, or applications filed in at least two patent authorities, and do not have means to control for the importance of individual patents. Nonetheless they provide a helpful way to assess the companies and nations involved in LED and SSL research in general and in specific technological sub-domains. Some of the leading companies and nations are reported on. The data show Samsung's rapid rise to prominence in these technologies. They indicate a greater role of nations other than the U.S. than has been noted in previous patent analyses, since the tendency of applicants to file predominantly in their home countries has meant that counts based solely on U.S. patents have missed large numbers of non-U.S. applicants active in this technology while still counting U.S. applicants that filed solely in the U.S. They reveal growing activity in Asia, partly in Korea because of Samsung's role, and partly in Taiwan and mainland China.

Recently, many researches focus on healthy lighting with sunlight. A Natural Light Guiding System includes collecting, transmitting, and lighting parts. In general, the lighting module of the Natural Light Guiding System only uses scattering element, such as diffuser, to achieve uniform illumination. With the passive lighting module, the application of the Natural Light Guiding System is limited because sunlight is dynamic source. When the sunlight is weak at morning, at evening, or on cloudy day, the illumination system is fail. In this paper, we provide an active lighting module that includes the lighting part of Natural Light Guiding System, LED auxiliary sources, optical elements, and optical detector. We use optical simulation tool to design and simulate the efficiency of the active module. The optical element can redistribute the sunlight only, LED light only, or sunlight with LED light to achieve uniform illumination. With the feedback of the detector, the active lighting module will adjust the intensity of LED to provide a steady illumination. Moreover, the module could replace the backlight module of LCD TV when the house has Natural Light Guiding System for saving energy and higher performance of image.

To design the layout of LED light sources(called as LEDs) in a medium or large LED-based lighting system to optimize the system's performance in illuminance, uniformity and heat dissipation by developing a Genetic Algorithm, the searching space formed by x,y, z coordinates and rotation angles of an LED light source will be rather huge as to paralyze the evolution program. Hence, we propose the idea of representative LED sources (called as representatives), which are parts of LEDs. In this paper, we will develop some a Genetic Algorithm to search for suitable representatives to make the evolutional design of a programmable Fresnel lens for the mentioned lighting system feasible. Based on the designed programmable Fresnel lens, develop another Genetic Algorithm to arrange the layout of LEDs, including locations and orientations of LEDs, to let the lighting system's performance be further enhanced.

There exists a fundamental trade-off relation between color rendering index (CRI) and luminous efficacy; in other words, improvements in one are generally detrimental to the other. We analyze and demonstrate through simulation that phosphor-converted white LEDs with dual-blue emitting active regions, as opposed to single-blue emitting active regions, significantly enhance color rendering ability while maximizing the output luminous flux. The improvements are achieved over a broad range of correlated color temperatures.

Light-emitting diodes (LEDs) are a major discovery in twenty-one century for its advantages including small size, long lifetime, low voltage, high response and good mechanical properties. It is an environment-friendly product and maybe becomes a lighting source in future. In the other way LED lighting also is used for the lighting source of cosmetology. LED phototherapy provided medicine with a new tool capable of delivering light deep into tissues of the body, at wavelengths that are biologically optimal for pain treatment and holistic healing. The illumination efficiency is one of the key indexes for the LED phototherapy. LEDs were arranged on a disk of diameter of 100mm with different array types: a radial, a rhombus, an octagon, and a square. Then the LEDs with view angle of 120 degree were used for the lighting sources. Trace-Pro software was used for the optical simulation. The array types of radial and square were better than those of rhombus and octagon for illumination efficiency. In the mixture efficiency of a radial array was observed by different distances from 1mm to 100mm. However lighting could reach the well mixture after the treatment distance of 30mm by optical simulation. The view angle could reach ±60 degree at the treatment distance of 50 mm for the LED phototherapy mockup.

Many researches have been devoted to enhance the light extraction of light emitting diodes (LED). In some designs of LEDs, an absorbing substrate cannot be avoided. To prevent the emitted light from being absorbed by the substrate, a highly reflective mirror called distributed Bragg reflectors (DBR) is employed between the substrate and the active layers. In addition, the DBR layers are doped to conduct current. In our study, we have n-GaAs as the substrate, n-AlGaAs / AlAs as the DBR, multiple quantum wells (MQW) as the active layers, p-GaP as the window layer. The choices of the dopant for the DBR are Si and Te. However, the resultant LEDs have different performance. The one doped with Si in DBR (DBR:Si) performs poorly. Our investigation shows that the optical properties of DBR:Si degrade dramatically because of the existence of AlGaInP (part of MQW) layer above and the subsequent high temperature annealing in p-GaP layer growth. Either condition alone cannot yield the degradation. Conversely, the optical properties of DBR:Te do not change significantly even though it undergoes the same processes to grow the subsequent layers. The result indicates a sophisticated interaction between DBR:Si and AlGaInP layers during the high temperature annealing process for the growth of p-GaP. The study provides the insight on the influence of the dopant to the optical properties of DBR in LED devices.

Influence of the high-power laser radiation on the piezoelectric resonance in the nonlinear-optical KTiOPO₄ crystal was observed. Equivalent crystal temperature can be directly determined from the piezoelectric resonance frequency during interaction of the laser radiation with crystals. Frequency kinetics of the different piezoelectric resonances of the KTiOPO₄ crystal were observed for the different pump laser powers up to 20 W. The KTiOPO₄ optical absorption coefficient and the amplitude of the crystal inhomogeneous temperature distribution were obtained from the kinetics data. A theoretical model of the piezoelectric resonances on the basis of the Rayleigh-Ritz method is proposed.

The optical and structural properties of InN layers grown by 'High Pressure Chemical Vapor Deposition' (HPCVD) using a pulsed precursor approach have been studied. The study focuses on the effect of ammonia precursor exposure time and magnitude on the InN layer quality. The samples have been analyzed by X-ray diffraction, Raman scattering, infra red reflectance spectroscopy and photoluminescence spectroscopy. Raman measurements and X-ray diffraction showed the grown layers to be single phase InN of high crystalline quality. The E2(high) Raman mode showed FWHM's as small as 9.2 cm^-1. The FWHM's of the InN(0002) X-ray Bragg reflex in the 2Θ-Ω- scans were around 350 arcsec, with rocking curve values as low as 1152 arcsec Photoluminescence features have been observed down to 0.7 eV, where the low energy cutoff might be due to the detector limitation. The analysis of the IR reflectance spectra shows that the free carrier concentrations are as low as as 3.3•10¹⁸ cm^-3 for InN layers grown on sapphire substrates.