This PDF file contains the front matter associated with SPIE Proceedings Volume 8484 including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Color constancy and color maintenance are key issues in the context of the utilization of light-emitting diodes (LEDs) for general lighting applications. For a systematic approach to improve the white light quality of phosphor converted LEDs and to fulfill the demands for color temperature reproducibility and constancy, it is imperative to understand how compositional, optical and thermal properties of the color conversion elements (CCE), which typically consist of a phosphor particles embedded in a transparent matrix material, affect the correlated color temperature of a white LED source. Based on a combined optical and thermal simulation procedure, in this contribution we give a comprehensive discussion on the underlying coherences of light absorption, quantum efficiency and thermal conductivity and deduce some strategies to minimize the temperature increase within the CCE in order to maintain acceptable color variations upon device operation.

A wings type imbedded electrode was introduced into the lateral light emitting diodes (WTIE-LEDs) to improve the light shading effect from the metal electrode of LED. The wing type imbedded contact structure was expected to eliminate the light shading of electrode and bonding wire, and further increased the light extraction and light output power. At 100 mA injection current, the WTIE-LED structure enhanced the output power of 41.6% as compared with that of conventional sapphire-based LEDs (CSB-LEDs) Moreover, the output power of the packaged WTIR-LED and CSB-LED is 70 and 88.94 mW, respectively, at the same injection condition. A 27% enhancement of light output power was achieved. Therefore, using the imbedded contact to reduce light shading would be a promising prospective for vertical LEDs to achieve high output power.

The high-temperature operation up to 350°C of glass phosphor layer for using in converted white light-emitting diodes is demonstrated. The results showed that the phosphor-converted white light-emitting diode (PC-WLEDs) maintained good thermal stability in lumen, chromaticity, and transmittance characteristics at the high temperature up to 350°C. The lumen degradation, chromaticity shift, and transmittance loss in glass based high-power PC-WLEDs under thermal aging at 150, 250, 350, and 450°C are presented and compared with the silicone based high-power PC-WLEDs under thermal aging at 150 and 250°C. The result clearly indicated that the glass based PC-WLEDs exhibited better thermal stability in lumen degradation, chromaticity shift, and transmittance loss than the silicone based PC-WLEDs. The advantages of glass doped encapsulation in high temperature PC-WLEDs could be arisen from the material property of glass transition temperature 567°C higher than silicone of 150°C. These newly developed high-temperature glass based PC-WLEDs are essentially critical to the application of LED modules in the area where the high-power, high-temperature, and absolute reliability are required for use in the next-generation solid-state lighting.

Lifetime is one of the most important characteristics of white LEDs for the solid state lighting industry and end users. The measurement uncertainties should be controlled well to ensure consistent measurement results. This paper gives uncertainty analysis in the measurement for the L50 lifetime of white LEDs. The exponential model is assumed for LEDs’ light output degradation, and an Eyring model is used for accelerated life test. The influences of photometric measurement instruments, measurement duration and interval, junction temperature, input current, current accelerating index and activation energy are analysed. The analysis method introduced in this paper can be referenced for other related analysis, and the results are important to the practices in LED lifetime measurement.

Traditional light sources were required to provide stable and uniform illumination for a living or working environment considering performance of visual function of human being. The requirement was always reasonable until non-visual functions of the ganglion cells in the retina photosensitive layer were found. New generation of lighting technology, however, is emerging based on novel lighting materials such as LED and photobiological effects on human physiology and behavior. To realize dynamic lighting of LED whose intensity and color were adjustable to the need of photobiological effects, a quantitative dimming method based on Pulse Width Modulation (PWM) and light-mixing technology was presented. Beginning with two channels’ PWM, this paper demonstrated the determinacy and limitation of PWM dimming for realizing Expected Photometric and Colorimetric Quantities (EPCQ), in accordance with the analysis on geometrical, photometric, colorimetric and electrodynamic constraints. A quantitative model which mapped the EPCQ into duty cycles was finally established. The deduced model suggested that the determinacy was a unique individuality only for two channels’ and three channels’ PWM, but the limitation was an inevitable commonness for multiple channels’. To examine the model, a light-mixing experiment with two kinds of white LED simulated variations of illuminance and Correlation Color Temperature (CCT) from dawn to midday. Mean deviations between theoretical values and measured values were obtained, which were 15lx and 23K respectively. Result shows that this method can effectively realize the light spectrum which has a specific requirement of EPCQ, and provides a theoretical basis and a practical way for dynamic lighting of LED.

We investigated the effects of SiN_x interlayers on the structural and electrical properties of nonpolar a-plane (11-20) GaN grown on r-plane (1-102) sapphire substrates by metal–organic chemical vapor deposition (MOCVD). The Nomarski optical microscope images showed that the deposition conditions of the SiN_x layer could strongly affect the a-plane GaN surface morphology due to the different SiN_x coverage. Basal-plane stacking faults (BSFs) and threading dislocation (TD) densities were reduced in the a-plane GaN samples with high SiN_x coverage and multiple SiN_x-treated GaN interlayers. These results indicate that TD reduction is associated with an increase in the 3D growth step and with the blocking of TD propagation. From on-axis (11-20) X-ray rocking curve (XRC) measurements, the anisotropy of full width at half maximum (FWHM) can be attributed to the crystal mosaicity due to insertion of different SiN_x interlayers. The anisotropy of sheet resistance between the c-and m-axis was also clearly seen in a-plane GaN samples with a high density of defects, which was attributed to the BSFs as scattering centers.

Photonic crystals (PhCs) were typically fabricated on the light emitting surface of light emitting diodes (LEDs) to improve light extraction, which is regarded as the weak coupling between the laterally propagated light in the epi-layers and the surface nanostructure. This work demonstrates GaN-based LEDs with the PhC structure on the mesa surface and nanohole arrays surrounding the light emitting mesa. Our new device (SHLED) shows a 56% higher optical output power than the planar structure (PLED), as compared with the 40% improvement of the surface PhC device (SLED) over PLED. The output power of SHLED is higher than that of SLED due to the enhanced diffraction of low order modes propagated in the lateral direction, in addition to the higher order mode light diffraction from the surface PhCs. From the relative angular spectra, the interaction of in-plane optical wave with the nanoholes (which are etched through MQWs) is much stronger than that with surface PhCs, suggesting an efficient light diffraction to the surface normal by nanoholes.

For a systematic approach to improve the white light quality of phosphor converted light-emitting diodes (LEDs) for general lighting applications it is imperative to get the sources of error for color constancy under control. In this context, it is essential to gain a deeper insight how the individual components of an LED package may contribute to color deviation. Typically, both monochromatic and phosphor converted light-emitting diodes are finally encapsulated by a pristine silicone layer in order to prevent mechanical damage of the LED packages. In this contribution we focus on the shapes of such encapsulation layers and discuss, based on an optical simulation procedure, their impact on the color temperatures of phosphor converted white LEDs as well as the ramifications of manufacturing imprecision of these shapes on the constancy and reproducibility of a desired color temperature.

In the past decade, there has been increased interest in energy-efficient lighting as energy resources become higher in demand. Street lighting and outdoor lighting are applications that are rapidly changing from the incumbent high-pressure sodium (HPS) to newer technologies such as light-emitting diode (LED) or induction-type lamps. There is evidence that certain populations believe LED streetlights and area lights to produce more glare than HPS luminaires. A number of differences exist between new and traditional light sources besides efficiency. These include spectral power distribution (SPD), source luminance, beam intensity distribution, and the number of sources needed to achieve intended light levels. Many field studies and laboratory studies have shown a relationship between glare and SPD, with most studies suggesting that sources more weighted in short wavelengths have an increased likelihood of discomfort glare. A study to assess the effect of different SPDs on perception of discomfort glare was conducted. Subjects were shown a white-light LED array against a luminous background with one of three different SPDs (blue, white, or yellow). As well, different intensities of light from the array and from the background were used. For the range of conditions evaluated, the presence of any luminous background significantly reduced the perception of discomfort glare from the LED array. The blue background reduced perception significantly less than the white or the yellow backgrounds. The implications for solid-state lighting systems such as outdoor array lighting are discussed.

The control of emission characteristics is of great importance as more specific wavelengths for applications are in demand with respect to nitride materials. Detailed investigations have been carried out to understand the emission states in multi quantum wells (MQWs) of Indium Gallium Nitride and Single Quantum well Aluminum Gallium Nitride structures using structural and optical investigations. The effect of growth parameters including the well thickness and the composition has been investigated and will be presented in detail.

A monolithically integrated multi-wavelength LED based on selective dielectric cap intermixing is investigated experimentally. The proposed LED emits radiation with multiple wavelength peaks from one compact easy to fabricate quantum well (QW) structure. Each wavelength has an independent emission power control, allowing the LED to radiate one or more wavelengths simultaneously. The LED material is an AlGaAs/GaAs QW p-i-n heterostructure. The device is divided into three selectively intermixed regions using an impurity-free vacancy induced intermixing technique creating localized intermixed areas. Each region is intermixed to varying extent resulting in different luminescence peaks and by separately addressing each section with its electrical current, the net emission spectrum can be fully controlled. The fabrication process starts with the growth of a 400nm thick layer of SiO₂ over the whole sample using plasma enhanced chemical vapor deposition. Three regions with different SiO₂ thicknesses are defined via two photolithographic and subsequent reactive ion etching steps. The sample is then annealed at 975°C for 20s to activate the intermixing of the constituent atoms of the quantum well and barrier materials. The degree of intermixing is determined by the thickness of the SiO₂ cap. After removal of the SiO₂ cap, contact stripes are evaporated on each region to act as an independent intensity power control for that region. Experimental results have shown that a controllable 10nm, 21nm and 33nm blue shifts of the peak wavelength of emission from that of the as-grown sample corresponding to 0, 100nm, and 400nm thick SiO₂ caps respectively.

High indium composition InGaN films were co-deposited on u-GaN templates using low temperature (300°C) pulsed laser deposition (PLD). The du-composition target consisted of a 3-inch indium sheet drilled with periodic rectangular holes mounted on a normal GaN wafer. By changing the ratio of the holes areas to total sheet area, the indium concentration in two InGaN films was set to 33% and 60%. The structural and optical characteristics of these films are investigated through isochronal and isothermal annealing. X-ray diffraction (XRD) and cathodeluminescence results for the 33% sample exhibited no significant differences in line-shape and peak position even after annealing at 800°C for 100 minutes. In contrast, the XRD peak of 60% sample became broadened under the same annealing condition. This slight inhomogeneity in composition also resulted in two visible peaks in the photoluminescence spectrum. Although the optical properties of the 60% sample can be considered merely acceptable, the advantages of applying PLD to the growth of high thermal stability and high indium composition InGaN have been made clear. The PLD technique shows promise for developing long wavelength devices.

An attempt has been made to fabricate p-ZnO by direct doping (codoping) of ZrN into ZnO thin films. The ZrN codoped ZnO (ZNZO) thin films of different concentrations (ZrN= 1, 2 and 4 mol %) have been grown on sapphire substrates by RF magnetron sputtering. The grown films have been characterized by X-ray diffraction (XRD), Hall effect measurement, photoluminescence (PL) and time-of-flight secondary-ion mass spectroscopy (ToF SIMS) analysis. XRD studies reveal that all the films are preferentially oriented along (002) plane. The Hall measurement showed that 1 and 2 mol% ZNZO films exhibit n-type conductivity due to the insufficient amount of nitrogen incorporation. However, 4 mol% ZNZO film showed p-type conduction as the sufficient amount of nitrogen has been incorporated into the film. The resistivity and hole concentration of the fabricated p-ZnO have been found as (1.92×10-1 Ωcm) and (2.76 x 10¹⁸ cm^{- 3}) respectively. The red shift in near-band-edge emission observed from PL evidenced the formation of p-conductivity in ZNZO films. The obtained p-conductivity has been well supported by XRD and PL studies. The presence of dopant in the film has been confirmed by ToF-SIMS depth profile analysis.

The dependency of the structural and optoelectronic properties of InN thin films grown by high-pressure chemical vapor deposition technique on the group V/III molar precursor ratio has been studied. X-ray diffraction, Raman spectroscopy, and IR reflectance spectroscopy have been utilized to study local- and long-range structural ordering as well as optoelectronic properties of the InN epilayers grown on crystalline sapphire substrates. The investigated InN epilayers were grown with group V/III molar precursor ratio varying from 900 to 3600, while all other growth parameters were kept constant. For a group V/III precursor ratio of 2400, the full width-half maximum of the Raman E₂(high) mode and XRD (0002) Bragg reflex exhibit minimums of 7.53 cm⁻¹ and 210 arcsec, respectively, with maximized grain size and reduced in-plane strain effect. FTIR data analysis reveals a growth rate of 120 nm/hr, a carrier mobility of 1020 cm²V⁻¹s⁻¹, and a free carrier concentration of 1.7×10¹⁸ cm⁻³ for a V/III ratio of 2400. The Raman analysis indicate that non-polar E₂(high) mode position remains unaffected from a changing V/III ratio; whereas, polar A₁(LO) mode position significantly changes with changing V/III ratio. Optical analysis also suggests that LO-phonon correlates with free carrier concentration (n_e) and TO-phonon correlates with free carrier mobility (μ) in the InN epilayers.

Quaternary III-V compound InAlGaP, especially In0.5(Al_xGa_1-x)0.5P which is lattice matched with GaAs, are important materials for visible red-green light emitting diode (LED) and laser diode (LD), solar cell and other optoelectronic and electronic device applications. A set of In_0.5(Al_xGa_1-x)_0.5P thin films on GaAs substrates with a wide range of x up to ~80%, were grown by low pressure metalorganic chemical vapor deposition (MOCVD) and studied by a variety of nuclear science and optical analytical techniques, including Rutherford Backscattering Spectrometry (RBS), Raman scattering, photoluminescence (PL), Photoreflectance (PR) and FTIR. Temperature dependent PL-PR measurements over 10-300 K presented the band gap of these InAlGaP materials and variations with composition x and temperature (T). RBS was used to measure the microstructure of AlInGaP films, and through simulation, determine the film thickness and composition precisely. RBS measurement and simulation results indicate a quite fuzzy in the two interfaces, i.e. that there exists diffusion in the majority samples, especially between the AlInGaP layer and substrate. For a certain number of incoming He+ ions,we have proposed a way to determine the error bar by RBS successful. For this series of samples, the error bar of content is around ±1.5%. The error bar of thickness is around ±5.0nm. Different InAlGaP films with different composition and thickness may present different error bars. The results illuminate that RBS is a precise tool to analysis the microstructure of quaternary semiconductor AlInGaP/GaAs samples.

Two comparative blue emitting InGaN/GaN multiple quantum well (MQW) structures, for lighting and laser diode applications, with and without pre-strained layer, were grown by MOCVD. Temperature dependent photoluminescence (TDPL) and time-resolved (TR) PL were used to study their optical and transient properties. PL signals from InGaN MQWs were divided into two parts: one is the band to band transition of InGaN; the other is the broad defect band. It is indicated that the InGaN/GaN MQW structure with prestrained layer has larger activation energy. TRPL measurements were performed in 10-300 K and with the detection wavelength cross over the emission peak. It is found that the MQW sample with prestrained layer has deeper localization depth. Temperature dependence of PL decay time shows an interesting behavior of an increase from 10K to 30K and then a decrease till 300K.

The optical lens model which is constructed by the method of luminous flux mapping and reshaped according to the target grids modification is demonstrated in this study. The design method was tried on designing LED road lighting devices which were further confirmed by optical simulations and verified by experiments.

We demonstrate the feasibility of using a Vertically-Aligned Polymer-Stabilized Liquid Crystal (VA-PSLC) film, which is also known as LC gel, as a transparent image generator to form a see-through display system. This is achieved, in its simplest form, by projecting a collimated LED light source onto a transparent glass screen, with the image generated by the scattered light from the VA-PSLC. By moving the observer’s head slightly away from the incident light specular reflection direction, a clear image can be observed on the transparent glass screen together with the background objects that are behind the screen. From our experimental results, this see-through display system using VA-PSLC transparent image generator can achieve a fast response time (with rise time of ~10 ms and fall time of ~5ms) and an acceptable contrast ratio (< ~100:1). The driving voltage is about 15~20V. Further improvements can be achieved by further optimizing the LC material/monomer parameters, device fabrication process/conditions and the optical system setup. In this system, polarizers are not required so that very high light efficiency can be obtained.

We have developed an image-based measurement method on UGR (unified glare rating) of interior lighting environment. A calibrated DSLR (digital single-lens reflex camera) with an ultra wide-angle lens was used to measure the luminance distribution, by which the corresponding parameters can be automatically calculated. A LED lighting was placed in a room and measured at various positions and directions to study the properties of UGR. The testing results are fitted with visual experiences and UGR principles. To further examine the results, a spectroradiometer and an illuminance meter were respectively used to measure the luminance and illuminance at the same position and orientation of the DSLR. The calculation of UGR by this image-based method may solve the problem of non-uniform luminance-distribution of LED lighting, and was studied on segmentation of the luminance graph for the calculations.

White light-emitting diodes (LEDs) consisting of a nitride-based blue LED chip and phosphor are very promising candidates for the general lighting applications as energy-saving sources. Recently, donor-acceptor doped fluorescent SiC has been proven as a highly efficient wavelength converter material much superior to the phosphors in terms of high color rendering index value and long lifetime. The light extraction efficiency of the fluorescent SiC based all semiconductor LED light sources is usually low due to the large refractive index difference between the semiconductor and air. In order to enhance the extraction efficiency, we present a simple method to fabricate the pseudo-periodic moth-eye structures on the surface of the fluorescent SiC. A thin gold layer is deposited on the fluorescent SiC first. Then the thin gold layer is treated by rapid thermal processing. After annealing, the thin gold layer turns into discontinuous nano-islands. The average size of the islands is dependent on the annealing condition which could be well controlled. By using the reactive-ion etching, pseudo-periodic moth-eye structures would be obtained using the gold nano-islands as a mask layer. Reactive-ion etching conditions are carefully optimized to obtain the lowest surface reflection performance of the fabricated structures. Significant omnidirectional luminescence enhancement (226.0 %) was achieved from the angle-resolved photoluminescence measurement, which proves the pseudo-periodic moth-eye structure as an effective and simple method to enhance the extraction efficiency of fluorescent SiC based white LEDs.

This study presents a structure design and process method for lens type LED package. Dome type or side-emitting-enhancement silicone lens without molding process are achieved. The ceramic ring is adopted as the confine for the encapsulant. The surface intension along the sidewall of ceramic ring and silicone surface, the cohesion force and the gravity of silicone determine the shape of dome type silicone lens. The cone shape tooling coated with a releasing material is immersed into the dome type silicone lens before the silicone fully hardening. After curing simultaneously, to remove the tooling from package, the package with side-emitting-enhancement silicone lens is finished. With the mentioned architecture and process, this LED package herein has three merits, (1) to improve light extraction efficiency: reduce the chance of total internal reflection by the geometry of dome type silicone lens. (2)To enhance the flexibility of LED package design, the die placement location would be constrained by the mold in the traditional package process. (3) Mold-less side-emitting-enhancement silicone lens. Furthermore, two types of cone shape tooling are implemented and compared for side-emitting-enhancement silicone lens. Measurement results show the ratio between the lens high and lens radius could achieve 0.9:1. The view angles of dome type and side-emitting-enhancement LED packaged devices can reach 153° and 180 °, respectively. As using the same brightness grade of LED chip, the luminous flux is increasing 15% as compared the dome type package with the commercial PLCC (Plastic Leaded Chip Carrier) type package. The luminous flux of side-emitting-enhancement LED package decreases 8% as compared with the dome type one.

Scientific and technological progress of recent years in the production of the light emitting diodes (LEDs) has led to the expansion of areas of their application from the simplest systems to high precision lighting devices used in various fields of human activity. However, for all technology development at the present time it is very difficult to choose one or another brand of LEDs for realization of concrete devices designed for the implementation of high precision spatial and color measurements of various objects. In the world there are many measurement instruments for determining the various parameters of LEDs, but none of them are not capable to estimate comprehensively the LEDs spatial, spectral, and color parameters with the necessary accuracy and speed. This problem can be solved by using an automated hardware-software system for LED’s verification and certification, developed by specialists of the OEDS chair of National Research University ITMO in Russia. The paper presents the theoretical aspects of the analysis of LED’s spatial, spectral and color parameters by using mentioned of automated hardware-software system. The article also presents the results of spatial, spectral, and color parameters measurements of some LEDs brands.

We presents graphene-based reflective electrode on Ag films as a reflectively conductive layer for flip-chip GaN-based LEDs to improve optoelectronic characteristics of LEDs. The Ag/graphene films demonstrate thickness of about 200 nm and surface roughness. As annealing at temperature increases from 500°C to 800°C, the location of peak increases from 22.5° to 26.2° with the peak intensity becomes stronger. This may be attributed to the reduction of oxygen functional group. A graphene has first and second Raman-active modes at D band (1350 cm^-1) and G band (1592 cm^-1), respectively. Optimal conditions for graphene/Ag films contact of the sheet resistance is the smallest value by after heat treatment at temperatures of 800 °C. Further, graphene/Ag films were also applied to GaN-based light-emitting diodes to form an electrode with a p-type ohmic contact.

High power light-emitting diodes (HP-LEDs) always are applied for energy-saving to replace the traditional light sources. HP-LEDs lighting has been regarded in the next generation lighting. In this study, the RGY colors enhance of whit LED lighting was researched and modulated by artificial neural network (ANN). An ANN model was used to investigate the correlated color temperature (CCT) and luminous flux (Lux) for the white LED enhanced with different power of single RYG LEDs. The starting color temperature of the white LED will be set at 7500K (D75 white light standard), then changed the voltage of the single LED of the red, green or yellow, respectively, to find the best tuning function for the color temperature and luminous efficiency. These results exhibited that changing the voltage of red LED had the broader color temperature from 7500 K to 1500 K than the range of green and yellow LEDs from 7500K to 8200K and 7500K to 4700K, respectively. Then, these experimental results were used as input data for the training model. After the learning model was completed, an analysis was used to obtain the internal representation of the color information by the responses of the individual chips of the three hidden units in the middle layer. Identification rate of data would be achieved to 100% by the neural network pattern-recognition tool. Anyway, the correlation coefficient could reach to 99% by the ANN fitting tool for the color enhancement.

Gold-indium metal bonding method was used in this study to increase the product yield of vertical light emitting diodes (LEDs) during laser lift-off (LLO) process. The vertical GaN LED transferred onto Si substrate presented good electrical and optical properties due to the existence of high reflective mirror and texture surface. The chip size and dominant wavelength for vertical type LED are 40×40 mil2 and 450 nm. The optimal conditions of temperature and pressure for 2-inch wafer bonding are set of 200oC and 100 kg/inch², respectively. The products yield of light output power, forward voltage and leakage current are 96 %, 96.4% and 61.2%, respectively. After aging test, the characteristics decay of light output power, forward voltage and leakage current are less than 4%. Summarization of optical and electrical properties, the total yield of these LEDs products is about 60 %.

The influence of structural and optoelectronic properties of InN epilayers on the duration of initial nucleation has been studied. High pressure chemical vapor deposition (HPCVD) has been utilized to deposit InN epilayers on GaN/sapphire (0001) templates at a reactor pressure of 15 bar. The initial nucleation period was varied between 10 s and 60 s, leaving all other growth parameters constant. The structural properties of the grown samples have been investigated by X-ray diffraction (XRD) spectroscopy and Raman spectroscopy. The optoelectronic properties were analyzed by Fourier transform infra-red (FTIR) spectroscopy. The layer thickness, free carrier concentration and void fraction were obtained by simulating IR spectra, using multi-layer stack model for epilayers and Lorentz-Drude model for dielectric function. Raman, X-ray diffraction (XRD) and void fraction calculation results suggest that the optimum nucleation time is between 10 - 20 s. However, simulation results revealed that the free carrier concentration of the bulk layer does not show any significant dependency on the duration of initial nucleation.