This PDF file contains the front matter associated with SPIE Proceedings Volume 7954, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Unexpectedly the existence of a formerly unknown type of photoreceptor in the human eye has been proven about 10 years ago. Primarily sensitive in the blue spectral range it is responsible for transducing light signals directly into the brain, controlling essential biological functions like setting of the circadian clock or daytime activation. Recent scientific research has enabled beneficial applications. The paradigms for good lighting design are shifting and standardization activities have been started to build up a sound base for description and application of biologically effective lighting. Latest improvements of LED technology are now allowing realizeation of advanced lighting solutions based on SSL. Optimization of biological effects is possible while demands on good vision are maintained. As biologically effective lighting is addressing a second system besides vision in the human body a measure beyond lumen per watt is required for a proper description of energy efficiency.

Tunable LED illumination systems utilizing digital control can satisfy many user requirements for white and colored light. Such systems provide a powerful entry point for LEDs into general illumination applications. Parameters such as light level and color temperature can be used to change space ambience. Variation of spectral distribution can be used to trade between energy efficiency and color rendition. Studies have been carried out in a controlled laboratory environment and in a "real life" occupied space. This paper presents an exploration of methodologies used to assess subjective, preference-based traits.

Technologies are needed to provide information about the state of our circadian system to our conscious awareness such that we can take appropriate action to avoid and to correct light-induced circadian disruption. In addition to the implicit promises of solid-state lighting to improve energy efficiency and the quality of the visual environment, solid-state lighting also promises to maintain our health and well-being by precisely tailoring light and dark throughout the 24-hour day.

We had demonstrated several novel methods to improve efficiency droop behavior in GaN-based light-emitting diodes (LEDs). LEDs with different kinds of insertion layers (ILs) between the multiple quantum wells (MQWs) layer and n-GaN layer were investigated. By using low-temperature (LT, 780°C) n-GaN as IL, the efficiency droop behavior can be alleviated from 54% in reference LED to 36% from the maximum value at low injection current to 200 mA, which is much smaller than that of 49% in LED with InGaN/GaN short-period superlattices (SPS) layer. The polarization field in MQWs is found to be smallest in LED with InGaN/GaN SPS layer. However, the V-shape defect density, about 5.3×10⁸ cm^-2, in its MQWs region is much higher than that value of 2.9×108 cm^-2 in LED with LT n-GaN layer, which will lead to higher defect-related tunneling leakage of carriers. Therefore, we can mainly assign this alleviation of efficiency droop to the reduction of dislocation density in MQWs region rather than the decrease of polarization field. At second part, LEDs with graded-thickness multiple quantum wells (GQW) was designed and found to have superior hole distribution as well as radiative recombination distribution by simulation modeling. Accordingly, the experimental investigation of electroluminescence spectrum reveals additional emission from the previous narrower wells within GQWs. Consequently, the efficiency droop can be alleviated to be about 16% from maximum at current density of 30 A/cm² to 200 A/cm². Moreover, the light output power is enhanced by 35% at 20 A/cm².

Color homogeneity is a key issue for LED lighting. To achieve sufficient flux, efficiency and color rendering, LED luminaires have to use multiple LEDs, whose brightness and color properties differ. To mix greenish white LEDs using phosphor with red monochromatic LEDs is an especially promising approach to achieve both high effiency and good color rendering at warm white colors. However, even for luminaires using only white LEDs, color and brightness of the LEDs varies due to random selection within LED bins, or by using LEDs from different bins. For diffuse illumination, color mixing is not too difficult, but for collimated light, good color mixing is a key challenge to the optical system. Micro lens arrays are known to provide extremely good color mixing while increasing beam divergence only slightly. However, in their standard forms with (i) hexagonal lenslets or (ii) circular lenslets with blackened triangles, they create beam patterns with (i) sharp edged hexagonal or (ii) less efficient sharp edged circular distributions, instead of the round, soft edged beam shapes needed for general lighting. This is due to the fact that the lenslet shapes are imaged to the far field. It is not possible to choose the lenslet shapes freely: the lenslet edges depend on the lenslet positions, forming a Voronoi diagram. We present various approaches to perturb the regular lenslet positions, forming a smooth round beam, while keeping the superior properties of standard micro lens arrays.

A model based on density-activated defect recombination processes is proposed as a possible explanation for the efficiency droop in GaN-based lasers. The model yields very good agreement with experimentally measured efficiencies based on fit parameters that indicate the presence of two types of recombination centers that have different local distributions and recombination rates. The recombination rates of the two types are found to be very similar for devices operating at 530nm and 410nm.

In this paper we introduce a method allowing theoretical calculation of linearity and scale factor errors in linear position sensors based on bi-cell photodiodes. Such calculations are applied using three methods to compensate for scale factor temperature drift. An example based on data of a specific sensor was computed to illustrate how the sensor's dimensions and drift compensation method influence the scale factor and linearity errors of its volt-displacement characteristic.

We report the development of a flexible, rugged test bed for the purpose of testing various passive solar light collector configurations. An essential aspect in evaluating the performance of such collectors is to analyze its behavior under various illumination levels and planes of incident light. The test bed consists of a series of white LED assemblies which are digitally controlled using a micro-controller and is mounted on a rugged frame. The intensity levels of the LED can be controlled through a computer to emulate the sun's radiation effectively.

In absence of piezoelectric polarization along the growth axis, a- and m-plane green GaInN light emitting diodes manifest stable emission wavelength -- independent of the injection current density. The shift of the dominant wavelength is less than 8 nm when varying the forward current density from 0.1 to 38 A/cm². Furthermore, the light emitted from the growth surface of such non-polar structures shows a very degree of linear polarization. This is attributed to a strong valance band splitting in such anisotropically strained wurtzite GaInN quantum wells . Such light emitting diodes show a high potential for energy efficient display applications.

Improving the crystal quality of AlGaN epitaxial layers is essential for the realization of efficient III-nitride-based light emitting diodes (LEDs) with emission wavelengths below 365 nm. Here, we report on two different approaches to improve the material quality of AlGaN buffer layers for such UV-LEDs, which are known to be effective for the MOVPE growth of GaN layers. Firstly, we grew AlGaN on thin GaN nucleation islands which exhibit a threedimensional facetted structure (3D GaN nucleation). Lateral overgrowth of these islands results in a lateral bending of dislocation lines at the growing facets. Secondly, in-situ deposited SiN_x interlayers have been used as nano-masks reducing the dislocation density above the SiN_x layers. Both approaches result in reduced asymmetric HRXRD ω-scan peak widths, indicating a reduced edge-type dislocation density. They can be applied to the growth of AlGaN layers with an Al concentration of at least 20%, thus suitable for LEDs emitting around 350 nm. On-wafer electroluminescence measurements at 20 mA show an increase in output power by a factor of 7 and 25 for LED structures grown on 3D GaN nucleation and SiNx interlayer, respectively, compared to structures grown on a purely 2D grown low Al-content AlGaN nucleation layer. Mesa-LEDs fabricated from the LED layer sequences grown on buffers with SiN_x interlayer exhibit a low forward voltage of 3.8 V at 20 mA and a maximum continuous wave (cw) output power of 12.2 mW at 300 mA.

This paper discusses some of the advantages of nanowire structures for use in LEDs as well as the challenges that need to be overcome towards the realisation of real-world devices. Our experimental results pertain to group-III nitride nanowire structures grown by MBE. We present clear evidence that the catalyst-free growth approach on Si yields best results with respect to structural and optical material properties. We elucidate the mechanism of nanowire nucleation and the factors determining the initial nanowire diameter, discuss the issue of InGaN growth in small-diameter nitride nanowires and review the results reported for nanowire-based group-III nitride LEDs reported so far.

Although planar heterostructures dominate current solid-state lighting architectures (SSL), 1D nanowires have distinct and advantageous properties that may eventually enable higher efficiency, longer wavelength, and cheaper devices. However, in order to fully realize the potential of nanowire-based SSL, several challenges exist in the areas of controlled nanowire synthesis, nanowire device integration, and understanding and controlling the nanowire electrical, optical, and thermal properties. Here recent results are reported regarding the aligned growth of GaN and III-nitride core-shell nanowires, along with extensive results providing insights into the nanowire properties obtained using cutting-edge structural, electrical, thermal, and optical nanocharacterization techniques. A new top-down fabrication method for fabricating periodic arrays of GaN nanorods and subsequent nanorod LED fabrication is also presented.

The enhancement of light extraction efficiency of InGaN quantum well (QW) light emitting diodes (LEDs) was achieved by employing the refractive index matched TiO₂ microsphere arrays. The optimization studies of the dipping method and rapid convective deposition (RCD) method were carried out for the deposition of TiO₂ microsphere arrays onto LEDs. The 2-dimensional relatively close-packed and close-packed TiO₂ microsphere arrays were deposited by the using optimized conditions of the dipping method and RCD method, respectively. The light extraction efficiencies of LEDs under electrical injection were enhanced by 1.83 times by utilizing 520-nm diameter TiO₂ microspheres. This enhancement is primarily attributed to increase in the effective photon escape cone due to the matched index and spherical shape of TiO2 microstructures arrays.

EO/IR Nanosensors are being developed for a variety of Defense and Commercial Systems Applications. These include UV, Visible, NIR, MWIR and LWIR Nanotechnology based Sensors. The conventional SWIR Sensors use InGaAs based IR Focal Plane Array (FPA) that operate in 1.0-1.8 micron region. Similarly, MWIR Sensors use InSb or HgCdTe based FPA that is sensitive in 3-5 micron region. More recently, there is effort underway to evaluate low cost SiGe visible and near infrared band that covers from 0.4 to 1.6 micron. One of the critical technologies that will enhance the EO/IR sensor performance is the development of high quality nanostructure based antireflection coating. Prof. Fred Schubert and his group have used the TiO₂ and SiO₂ graded-index nanowires / nanorods deposited by obliqueangle deposition, and, for the first time, demonstrated their potential for antireflection coatings by virtually eliminating Fresnel reflection from an AlN-air interface over the UV band. This was achieved by controlling the refractive index of the TiO₂ and SiO₂ nanorod layers, down to a minimum value of n = 1.05, the lowest value so far reported In this paper, we will discuss our modeling approach and experimental results for using oblique angle nanowires growth technique for extending the application for UV, Visible and NIR sensors and their utility for longer wavelength application. The AR coating is designed by using a genetic algorithm and fabricated by using oblique angle deposition. The AR coating is designed for the wavelength range of 400 nm to 2500 nm and 0° to 40° angle of incidence. The measured average optical transmittance of an uncoated glass substrate between 1000 nm and 2000 nm is improved from 92.6% to 99.3% at normal incidence by using a two-layer nanostructured AR coating deposited on both surfaces of the glass substrate.

A new concept of a vertical In-Line deposition machine for large area white OLED production has been developed. The concept targets manufacturing on large substrates (≥ Gen 4, 750 x 920 mm²) using linear deposition source achieving a total material utilization of ≥ 50 % and tact time down to 80 seconds. The continuously improved linear evaporation sources for the organic material achieve thickness uniformity on Gen 4 substrate of better than ± 3 % and stable deposition rates down to less than 0.1 nm m/min and up to more than 100 nm m/min. For Lithium-Fluoride but also for other high evaporation temperature materials like Magnesium or Silver a linear source with uniformity better than ± 3 % has been developed. For Aluminum we integrated a vertical oriented point source using wire feed to achieve high (> 150 nm m/min) and stable deposition rates. The machine concept includes a new vertical vacuum handling and alignment system for Gen 4 shadow masks. A complete alignment cycle for the mask can be done in less than one minute achieving alignment accuracy in the range of several 10 μm.

The optical features of the internal dipole emission have major impact on the radiation pattern and overall device efficiency of organic light-emitting diodes (OLEDs). In recent years, the characterization of OLED emitter properties by optical analysis of far-field radiation patterns of OLEDs in electrical operation was established as an in situ investigation method. However, in order to observe the internal features of the dipole emission in the OLEDs far-field accurately, well adapted devices should be utilized to optically enhance the feature of interest. Although this is a crucial point, the potential of adapted devices to OLED characterization has not been investigated universally yet. In our contribution, we provide general directives how the OLEDs layered stack is to be designed in order to enable for precise measurements of the active optical properties of the emissive material (internal electroluminescence spectrum, profile of the emission zone and dipole moment orientation) by radiation pattern analyses. Basically, we utilize the fact that the distance of the emissive sites to the metal cathode is most crucial to enhance or suppress certain dipole contributions to the far-field. A model layered system is discussed and universal emitter positions suitable to determine the internal feature of particular interest at most accuracy are deduced.

Rare-earth doped oxyfluoride 75SiO₂:25PbF₂ nano-structured phosphors for white-light-emitting diodes were synthesized by thermal treatment of precursor sol-gel derived glasses. Room temperature luminescence features of Eu³⁺, Sm³⁺, Tb³⁺, Eu³⁺/Tb³⁺ and Sm³⁺/Tb³⁺ ions incorporated into low-phonon-energy PbF₂ nanocrystals dispersed in the aluminosilicate glass matrix and excited with UV(395 nm) and blue(405 nm) light emitting diodes was investigated. The luminescence spectra exhibited strong emission signals in the red(600, 610, 625, 646 nm), green(548, and 560 nm) and blue(485 nm) wavelength regions. White-light emission was observed in Sm/Tb and Eu/Tb double-doped activated phosphors employing UV-LED excitation at 395 nm. The dependence of the luminescence emission intensities upon annealing temperature, and rare-earth concentration was also examined. The results indicated that there exist optimum annealing temperature and activator ion concentration in order to obtain intense visible emission light with high color rendering index. The study suggest that the nanocomposite phosphor based upon 75SiO₂:25PbF₂ host herein reported is a promising contender for white-light LED applications.

White light-emitting diodes that use down-converting phosphors have been utilized in the illumination industry for several years. In many cases, little information needs to be known about the physics and performance of the phosphor itself to design, optimize, and simulate the light emission of the LED for the purpose of creating secondary optics. However, the importance of accurately accounting for the effect of the phosphor cannot be overstated when designing the LED package or when performing a tolerance analysis, for instance. The difficulties in gathering or measuring the relevant performance metrics of the phosphors are significant barriers to achieving accurate predictions in illumination software packages. This paper describes a simple, repeatable process to measure several phosphor performance metrics that are used, in turn, to create a model of the same phosphor in a commercially-available illumination software package. The measured values are used either as direct inputs or are used to derive the proper inputs for the software. Derivations and discussion about the software model are included. The performance of the simulated phosphor will then be compared and correlated to the physical measurements. Finally, a model of an LED that uses this phosphor model is built in software and its simulated performance is compared to measured values.

Many LED-based applications would benefit from more efficient and/or high lumen output devices that enable usage in both white and single color illumination schemes. In the present article we briefly review the materials research history leading to optical ceramic converters and discuss their typical characteristics. Recently demonstrated high performance values in terms of efficacy and external quantum efficiency in orange (amber) spectral region are described.

The light-emitting diodes (LEDs) with high external quantum efficiency (EQE) are usually fabricated on the patterned sapphire substrate (PSS). The PSS reduces the dislocation density in the GaN layer and enhances the light extraction efficiency (LEE) from the LED chip by scattering the light confined in GaN layer attributed to the critical angle between GaN (n=2.4) and sapphire substrate (n=1.7) (or air (n=1.0)). On the other hand, non-polar GaN and semipolar GaN are attracted much attention to eliminate the quantum confined Stark effect (QCSE). Recently, we have developed novel technology to grow non-polar or semi-polar GaN on the PSS with high quality and large diameter by metal-organic vapor phase epitaxy (MOVPE). For example, m-plane GaN grown on a-plane PSS and {112 (see manuscript)} plane GaN grown on r-plane PSS. The growth of c-plane GaN from the c-plane-like sidewall of the r-plane PSS results in {112 (see manuscript)} GaN on the r-plane PSS. The full widths at half maximum of X-ray rocking curves (FWHM-XRC) of the {112(see manuscript)} GaN along the azimuths parallel and perpendicular to the c-direction were 533 and 260 arcsec, respectively. Dislocation density of the GaN was approximately 2×10⁸ cm^-2. These non-polar and semi-polar GaN are expected to be suitable for novel GaN substrate or GaN template for LEDs.

Chemical lift-off (CLO) technique has been paid more attention since no damages will be induced to GaN epi-layer during the epilayer lift-off process. In this study two novel CLO approaches were used to separate GaN epilayer from sapphire substrate. One is using Ga₂O₃sacrificial layer deposited by pulsed laser deposition. The other is using a stripe patterned SiO₂grown by PECVD. Afterwards, the CLO of GaN epilayers grown on these two templates via metal organic chemical vapor deposition from sapphire substrate was successfully realized with a hydrofluoric acid as an etchant.

The challenges and approaches for high-efficiency InGaN quantum wells (QWs) light-emitting diodes (LEDs) are presented. The studies include designs, growths, and device characteristics of 1) InGaN-based QWs LEDs with enhanced matrix element for realizing green-emitting LEDs with high internal quantum efficiency, and 2) InGaN QW LEDs device structure with lattice-matched AlInN-barrier to suppress efficiency-droop in nitride LEDs. Other approaches to improve the efficiency of the nitride LEDs will be discussed as follow: 1) surface plasmon LEDs, 2) new growth approach for dislocation density reduction in GaN, and 3) novel approaches for light extraction efficiency improvement of III-Nitride LEDs.

In this paper we investigate the use of a patterned layer placed at the substrate / GaN interface region of a p-side up LED to improve light extraction and investigate the optimization of performance geometry by adjustment of geometrical parameters associated with the shaped structures including: side wall angle, side wall curvature, height and lattice constant. Performance is in each case evaluated in terms of angular extraction efficiency and far field angular beam profile. Comparisons are made between conventional large pitch patterned substrate (PSS) designs which have multiple wavelength length scales, and photonic crystal lattices which have a (sub) wavelength length scale. Physical mechanisms giving rise to the improvements are identified and discussed in each case. Overall a maximum improvement in extraction efficiency of 66% was obtained for a 4500nm pitch lattice of truncated cones.

In recent literatures, the quantum efficiency of conventional blue InGaN light-emitting diodes (LEDs) is quite limited under relatively high driving current with conventional GaN barriers due presumably to the poor injection efficiency of hole. In this study, the efficiency enhancement of blue InGaN LEDs with indium composition graded InGaN barriers is proposed. The energy band diagram, carrier concentration in the quantum wells, diagram of hole current, radiative recombination rate, L-I curves, and internal quantum efficiency are investigated numerically. The simulation results show that the InGaN LED with graded InGaN barriers has better performance over its conventional counterpart with GaN barriers due to enhanced efficiency of hole injection. The simulation results also suggest that under relatively high current injection, the internal quantum efficiency and output light power are markedly improved when the traditional GaN barriers are replaced by graded InGaN barriers. According to the improved optical properties, the new-designed LED has promising potential in solid state lighting.