This PDF file contains the front matter associated with SPIE Proceedings Volume 7058, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Much has been written about the daily challenge for survival faced by countless millions of developing world families and the overdeveloped world has offered a number of solutions by which those at the base of the economic pyramid (BOP) can help themselves. Light Up The World (LUTW), the global leader in bringing Renewable Energy (RE) based Solid State Lighting (SSL) to the developing world, offers yet another solution, and one that comes with a very high probability of success. In this paper we discuss: the critical role played by micro credit (banking for the poor); a typical example of a developing world community and their lighting needs and expenditures; how SSL can contribute positively to all eight of the Millennium Development Goals; the micro and macroeconomics of SSL at the BOP, its numerous societal benefits and its potential perverse outcomes; and thought there will always be a role for the donation based model, it is only through the market model that safe, healthy and affordable SSL will reach the majority of the BOP, such are the staggering numbers involved. LUTW's fundamental goal, through the facilitation of RE based SSL, is to improve the quality of life of those, who through no fault of their own, find themselves trapped in a cycle of poverty.

We propose an on-wafer heat relaxation technology by selectively ion-implanted in part of the p-type GaN to decrease the junction temperature in the LED structure. The Si dopant implantation energy and concentration are characterized to exhibit peak carrier density 1×10¹⁸ cm^-3 at the depth of 137.6 nm after activation in nitrogen ambient at 750 °C for 30 minutes. The implantation schedule is designed to neutralize the selected region or to create a reverse p-n diode in the p-GaN layer, which acts as the cold zone for heat dissipation. The cold zone with lower effective carrier concentration and thus higher resistance is able to divert the current path. Therefore, the electrical power consumption through the cold zone was reduced, resulting in less optical power emission from the quantum well under the cold zone. Using the diode forward voltage method to extract junction temperature, when the injection current increases from 10 to 60 mA, the junction temperature of the ion-implanted LED increases from 34.3 °C to 42.3 °C, while that of the conventional one rises from 30.3 °C to 63.6 °C. At 100 mA, the output power of the ion-implanted device is 6.09 % higher than that of the conventional device. The slight increase of optical power is due to the increase of current density outside the cold zone region of the implanted device and reduced junction temperature. The result indicates that our approach improves thermal dissipation and meanwhile maintains the linearity of L-I curves.

This paper is to design and fabricate an optical homogenizer with hybrid design of collimator, toroidal lens array, and projection lens for beam shaping of Gaussian beam into uniform cylindrical beam. TracePro software was used to design the geometry of homogenizer and simulation of injection molding was preceded by Moldflow MPI to evaluate the mold design for injection molding process. The optical homogenizer is a cylindrical part with thickness 8.03 mm and diameter 5 mm. The micro structure of toroidal array has groove height designed from 12 μm to 99 μm. An electrical injection molding machine and PMMA (n= 1.4747) were selected to perform the experiment. Experimental results show that the optics homogenizer has achieved the transfer ratio of grooves (TRG) as 88.98% and also the optical uniformity as 68% with optical efficiency as 91.88%. Future study focuses on development of an optical homogenizer for LED light source.

While still not common in day-to-day business, mobile robot platforms form a growing market in robotics. Mobile platforms equipped with a manipulator for increased flexibility have been used successfully in biotech laboratories for sample management as shown on the well-known ESACT meetings. Navigation and object recognition is carried out by the utilization of a mounted machine vision camera. To cope with the different illumination conditions in a large laboratory, development of an adaptive light source was indispensable. We present our approach of rapid developing a computer controlled, adaptive LED light within one single business day, by utilizing the hardware toolbox EasyKit and our appropriate software counterpart EasyLab.

A resonance tunnelling LED structure having a high efficiency, low droop and negligible wavelength shift with current is reported in this study. The LED structure contains a thick InGaN bottom spacer between an n-GaN contact layer and a multiple quantum well (MQW) active region, and a thin InGaN top spacer between the MQW and an AlGaN electron blocking layer (EBL). The observed high efficiency and negligible wavelength shift with applied current are attributed to the thick InGaN bottom spacer that nucleates V-pits and acts as a strain control layer for the MQW. The thick InGaN layer also provides an electron reservoir for efficient electron tunnelling injection into the MQW and reduces the electropotential difference between the n-emitter and the p-emitter, to suppress current leakage at high driving current and reduce droop. The top InGaN spacer was designed to act as a magnesium back-diffusion barrier and strain relief layer from EBL so as to obtain high efficiency.

A new phosphor technology for phosphor converted light-emitting diodes (pcLEDs) is presented. A polycrystalline ceramic plate (Lumiramic^TM) of Ce (III) doped yttrium gadolinium aluminum garnet (Y,GdAG:Ce) is combined with a blue LED to produce white light in the range of 5000 K correlated color temperature. Scattering and light extraction means of the Lumiramic ceramic color converter plates enable production of reliable and efficient white pcLEDs. Measurement of the optical properties of the Lumiramic plates before the final LED assembly allows pick and place packaging with exact targeting of the desired white color point of the LED. Combination with a red phosphor powder layer, coated onto the Lumiramic plate, results in high quality white pcLEDs with any color temperature required for the general lighting market.

We have made a GaN-based single nanopillar with a diameter of 300nm using the focused ion beam (FIB) technique. The micro-photoluminescence (μ-PL) from the embedded GaN/InGaN multi-quantum wells reveals a blue shift of 68.3 meV in energy. In order to explain the spectrum shift, we have developed a valence force field model to study the strain relaxation mechanism in a single GaN-based nanopillar structure. The strain distribution and strain induced polarization effect inside the multiple quantum wells is added to our self-consistent Poisson, drift-diffusion, and Schrodinger solver to study the spectrum shift of μ-PL.

The forward voltage U_f for single-die high-power light-emitting diodes (LEDs) driven at currents within a specific current interval is proportional to the diode junction temperature T . This correlation can be used to determine junction temperatures in lots of practical applications. However, multi-die high-power LED modules with multiple series or parallel connections of diode chips are believed to have a much greater potential to be used in general lighting than single-die packages. The current-voltage characteristics of a variety of multi-die LEDs, ranging from two to a few hundred dies, are recorded at different ambient temperatures. The results are used to model the forward voltage as a function of a generalized junction temperature. In multi-die LED modules these models allow analogous junction temperature determination as in single-die packages. The influence of drive current and drive mode (DC or PWM) on junction temperature is examined and compared for both single-die and multi-die packages. Apparently, junction temperature only significantly increases when a certain current level is exceeded, depending on the internal series resistance of the complete LED package. Moreover, combining U_f (T) models for single-die and multi-die LEDs allows for the characterization of thermal interactions between different dies of multi-die packages, whether they are switched on or not. The junction temperature of separate LED dies in multi-die modules can then be predicted and used for further diode characterization.

PdZn was used to improve the electrical properties of p-GaN annealed at low activation temperature for high efficiency green light-emitting diodes (LEDs). A hole concentration of p-GaN annealed at 600 °C with PdZn was almost 28 times higher than that of p-GaN annealed at 800 °C without PdZn. SIMS analysis showed that hydrogen concentration in p-GaN annealed with PdZn is decreased compared to that without using PdZn because the PdZn enhances hydrogen desorption from the Mg-doped p-GaN film at low temperature. The green MQW LED annealed at 600 °C using PdZn showed improved electrical characteristic and optical output power compared to that annealed at 800 °C without using PdZn. These results are attributed to the increase of hole concentration of p-GaN due to removal of hydrogen in p-GaN by PdZn and the decrease in thermal damage of MQW at low activation temperature.

Al₂O₃ films were deposited on the Zn face of ZnO (0001) substrates as a transition layer by atomic layer deposition (ALD). The as-deposited 20 and 50nm Al₂O₃ films were transformed to polycrystalline α-Al₂O₃ phase after optimal annealing at 1100°C after 10 and 20 minutes, respectively, as identified by high resolution x-ray diffraction (HRXRD). Furthermore, GaN and InGaN layers were grown on annealed 20 and 50nm Al₂O₃ deposited ZnO substrates by metalorganic chemical vapor deposition (MOCVD) using NH3 as a nitrogen source at high growth temperature. Wurtzite GaN was only seen on the 20nm Al₂O₃/ZnO substrates. Room temperature photoluminescence (RT-PL) shows the near band-edge emission of GaN red-shifted, which might be from oxygen incorporation forming a shallow donor-related level in GaN. Raman scattering also indicated the presence of a wellcrystallized GaN layer on the 20nm Al₂O₃/ZnO substrate. InGaN was grown on bare ZnO as well as Al₂O₃ deposited ZnO substrates. HRXRD measurements revealed that the thin Al₂O₃ layer after annealing was an effective transition layer for the InGaN films grown epitaxially on ZnO substrates. Auger Electron Spectroscopy (AES) atomic depth profile shows a decrease in Zn in the InGaN layer. Moreover, (0002) InGaN layers were successfully grown on 20nm Al₂O₃/ZnO substrates after 10min annealing in a high temperature furnace.

In our contribution we discuss structure-luminescence property relations of MSi₂O₂N₂:Eu (M = Ba, Sr, Ca) phosphors to explain the differences in excitability, emission band position and width. The differences in Eu²⁺ site coordination, number and size of sites lead to a shift of emission from M = Ba over M = Sr to M = Ca from cyan to yellow accompanied by an increased Stokes shift. Because of its favourable emission properties with a peak at ~ 538 nm SrSi₂O₂N₂:Eu was selected and optimized as down-conversion material for green pcLEDs. pcLEDs built with LUXEON^R thin-film flip chip (TFFC) LEDs show stable color points under a wide range of drive conditions (I ≤ 1A, T ≤ 150°C) as a consequence of the very high conversion efficiency of optimized SrSi₂O₂N₂:Eu color converters. Although cutbacks in color purity have to be made because of the broad band phosphor emission spectrum, efficacies of the discussed green pcLEDs are significantly higher compared to direct green emitting InGaN LEDs.

Phosphor converted white LEDs are becoming more and more attractive for general lighting applications because of the steadily increasing luminous efficacy numbers reported by LED-suppliers. Despite these high numbers, a further significant improvement step can be made when a low-to-medium brightness (<500 kCd/m²) source is acceptable. The wall plug efficiency of a blue LED is generally better than that of a conventional white LED made from the same die. To take full advantage of this, we have developed medium-brightness LED-modules (~150 kCd/m²) for general lighting in which the phosphor is applied remote from the blue LEDs. By direct comparison with modules in which conventional high power white LEDs with almost identical dies are applied, we have shown that on system level the remote phosphor modules can have up to 50% better efficacy. Using a downlight module as a carrier, we have shown that in the relevant color temperature range of 2700 to 4000K a high CRI (>80) can be obtained in combination with a high luminous efficacy, while the optical efficiency of the module can be over 85%. A module efficacy of over 100 lm/W at 4000K with CRI 80 seems to be within reach, with a long-term expectation of over 180 lm/W. The remote phosphor LED modules deliver well homogenized white light with a Lambertian radiation profile. They are ideal for general illumination, as they combine glare reduction with high system efficacy and enable high optical efficiencies of the luminaries. The RP modules enable forward compatibility by well defined interfaces and optical properties that are decoupled from the actual performance, form factor and number of LEDs in the module. The Philips Fortimo downlight system is based on this remote phosphor concept, featuring forward compatibility and a total system efficacy (including driver) of over 60 lm/W under operating conditions using currently available Luxeon Rebel emitters.

We demonstrate phosphor-free light-emitting diode (LED) by growing InGaN/GaN multiple quantum wells (MQWs) on the n-GaN microfacets. The white emission was realized by combining emissions from InGaN/GaN MQWs grown on cplane (0001), semipolar {11-22} and {1-101} facets which are selectively grown on n-GaN with trapezoidal shape arrays. The photoluminescence (PL) and electroluminescence (EL) measurement revealed that the long wavelength light was emitted from InGaN/GaN MQWs grown on c-plane (0001), while the short wavelength light was emitted from that of semipolar microfacets. The change in the emission wavelengths from each microfacets was due to the difference in the well thickness and In composition of each MQWs. The LED showed white emission at an injection current between 180 and 230 mA. These results suggested that white emission is possible without using the phosphor by combining emission lights emitted from microfacets.

With the power of light emitting diodes (LEDs) getting higher and higher, the issue of thermal management is getting much more important. In this paper, we discussed a new idea to get white light without using traditional phosphor and to enhance its extraction efficiency. Microlens is used for increasing external efficiency and shaping light pattern. The location of micro-lens is designed carefully by considering cup reflection. We also revealed that it is important to consider the angle of exit light from LEDs. The result shows our design is suitable for high color rendering index (CRI) application. At the same time, the uniform white light is approached as the light has been strongly diffused. Furthermore, we try to decrease the junction temperature as low as possible so as to increase stability and lifetime of LEDs. In order to maintain color mixing and dissipate heat, multi-chip or four pairs of electrodes which are electroplated with copper after bulk micromachining process within a silicon-based package are used. This novel packaging technique needs just a few processing steps and could be mass produced for nowadays high brightness light emitting diodes (HBLEDs).

Any cluster of light-emitting diodes (LEDs) can be modeled as a directional point source if the far-zone condition is met. A general condition is derived for the distance beyond which the far-zone approximation can be used in measuring or modeling propagation of light from an LED array. A simple equation gives the far-field condition in function of parameters of influence, such as LED radiation pattern, array geometry, and number of LEDs. We calculate the nearzone extension of clusters with LED radiation patterns of practical interest; for example Lambertian-type, batwing, and side emitting. The far-field condition is shown to be considerable shorter for high packaging density LED arrays. Moreover, the far-field dramatically changes in function of the beam divergence of the LED radiation pattern. For example, the near-zone of a square LED array with highly directional LEDs (small half-intensity viewing angle) can extend to more than 70 times the cluster size. This value is far from the classical rule of thumb (5 times the source size).

The optical and structural properties of Charge Asymmetric Resonance Tunneling (CART) structure InGaN/GaN multiquantum wells (MQWs) grown on sapphire by metalorganic chemical vapor deposition (MOCVD) have been investigated by optical measurements of temperature-dependent photoluminescence (PL), photoluminescence excitation (PLE) and time-resolved photoluminescence (TRPL), and high-resolution transmission electron microscopy (HRTEM). Two typical samples are studied, both consisting of six periods of CART InGaN wells with 3.3 nm thickness and with 8.5 nm thickness of GaN barrier, respectively, and two periods of InGaN wells with 2 nm thickness of 7 nm GaN barrier with different well growth-temperature of 797°C and 782°C, respectively. According to the PL measurement results, large values of activation energy are obtained. The decrease of well growth-temperature results higher In composition and also in the increase of composition fluctuation in the InGaN MQW region, showing the stronger carrier localization effect and large values of activation energy and Stokes' shift are obtained. The lifetime at the low-energy side of the InGaN peaks is longer for higher indium composition.

The market demands for innovative, efficient, small package and single-mode light sources are always high because of their broad applications in scientific, medical, industrial, and commercial fields. The high photoluminescence quantum yield, photophysical and photochemical stability, and tunable emission wavelength make quantum dots ideal for a new generation of solid state light sources. We report on the realization of various single-mode light sources in the visible spectral band by using semiconductor quantum dots. The effective use of a waveguide structure can help achieve the divergence control of the output light beam. This technique may benefit the development for next generation light emitting diodes, optical communication, intelligent optical sensors, microprocessors, and nanoscale optical imaging systems.

GaN epilayers and AlGaN/GaN superlattice structures have been deposited on (0001) ZnO substrates by metalorganic vapor phase epitaxy (MOVPE) using GaN and AlN buffer layers. The growth conditions were first optimized on GaN templates using N2 as carrier gas at relatively low temperature (<800 °C), which is suitable for GaN growth on a ZnO substrate. Experimental results show that high interfacial quality can be achieved in the superlattice by using TMIn as a surfactant. The optimized growth conditions were subsequently transferred to ZnO substrates. The influence of growth temperature on the material quality was studied. A proper growth temperature for both GaN cover layer and AlGaN/GaN superlattice can improve the structural and optical properties of the structures on ZnO. This improvement is verified using x-ray diffraction, atomic force microscopy and photoluminescence characterizations. The growth temperature must be chosen with these two factors in mind, with too low a growth temperature leading to poor quality material and too high a temperature causing reactions at the GaN/ZnO interface that degrade quality. AlN buffer layers on ZnO were also studied to increase subsequent GaN epilayer quality. Effects of buffer layer growth conditions on optical and structural quality were studied.

A chemical etching using a molten KOH+NaOH solution was developed to improve optical properties and leakage current of GaN light-emitting diodes (LEDs). The Photoluminescence (PL), capacitance-voltage (C-V) and currentvoltage (I-V) analysis showed that deep donor-acceptor pair (DDAP) defects were effectively removed by the chemical etching process. As a result, the forward and reverse leakage current of etched GaN LEDs were greatly decreased due to the reduced DDAP defects. The light output power of etched GaN LEDs was significantly improved by 45 % at an injection current of 20 mA due to the increased surface roughness of the p-GaN after the chemical etching. Furthermore, the light output power of etched GaN LEDs was saturated at an injection current of 340 mA compared to that of nonetched GaN LEDs which was saturated at 300 mA. In addition, the red-shift of electroluminescence (EL) peak wavelength in etched GaN LEDs was much smaller than that of non-etched GaN LEDs due to the suppression of Jouleheating by removal of DDAP defects.

To improve the optical efficiency and to reduce the number of optical components of LCD backlighting systems, two types of polarized-light backlights have been made from micro-structured birefringent polymeric layers. One type uses uniaxially oriented PEN and PET foils that have been structured by diamond-tool machining or by hot-embossing, and subsequently laminated onto a flat PMMA light guide. The second type uses a liquid crystalline polymeric layer laminated onto a micro-structured light guide. S-polarized light is preferentially extracted from the light guides. The efficiency has been measured to be 1.6-1.7 times higher than for a conventional backlight. Costs, thickness and complexity are decreased since no micro-prismatic brightness enhancement foils or reflective polarizer foils are needed.

Colloidal nanocrystal layers deposited onto the enclosure of InGaN light emitting diodes are demonstrated to operate as nano-phosphors for color conversion with high color stability. Dependent on the choice of the nanocrystal materials, either CdSe/ZnS or PbS nanocrystals are applied, the diode emission at 470 nm is converted to the red or to infrared light, with similar quantum efficiencies. The color conversion is further improved by dielectric mirrors with high reflectivity at the emission band of the nanocrystals, resulting in an almost doubling of the nanocrystal light extraction from the devices, which increases the nanocrystal device efficiency up to 19.1%.

An edge-backlight unit (EBLU) is applied as the light device to provide uniform light of liquid crystal display (LCD). Generally, the cathode cold fluorescent lamp (CCFL) is employed as the light source of BLU. With the advantages such as long durability, no mercury substance and good endurance of heavy impact, the light emitting diode (LED) is now accepted well known as available device for solid state lighting. To achieve the market requirement of the thin-film liquid crystal display (LCD) and the green-level product, the LED is replaced with the CCFL used in monitor in order to make display thinner, lighter, no Hg containing. In this paper, the integrated LED reflector is proposed because it enables the point-like light to distribute propagating-light line pattern successfully. To optimize the size and the radian of the reflector, our designed integrated LED reflector can achieve an optical efficiency more than 85%, and its light output length is 11 times of the input light source. Therefore, the integrated LED reflector not only can decrease the number of LED to save the built space, but also enhance the output efficiency. In the future, an integrated LED reflector could make displays thinner and brighter for backlight applications.

An array of spatially distributed LEDs can produce a desired illumination pattern by individually modulating each LED. A target image can be the desired lighting pattern so that the software could find the best solution to match it. Given a desired illuminance distribution on a target surface, the luminous flux of each single LED that most closely matches the desired distribution must be determined. We review a constrained least squares method for this problem. We show how the quality of the rendering depends on the number of LEDs, array-target distance, and the size of the illuminated area. In particular, as we observed, there is an optimum illumination distance, which is proportional to the square root of the target size and varies inversely with a power of the number of LEDs.

The concept of polarization engineering of InGaN quantum wells are discussed as an approach for improving the radiative recombination rate of III-Nitride based active region. Two quantum wells were discussed as follow: 1) staggered InGaN quantum well, and 2) type-II InGaN-GaNAs quantum well. 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 electron-hole 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 <b>k•p</b> 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 450-nm utilizing staggered InGaN QW show improvement in output power much higher than what is predicted theoretically. In addition to the staggered InGaN QW, type-II InGaN-GaNAs QW was also investigated theoretically with potential of implementation for high efficiency LEDs.

We report on the fabrication and characterization of hybrid polymer light emitting device (HPLEDs) with high brightness and simplicity in design with improved robustness than the conventional polymer light-emitting diodes. We demonstrate the incorporation of Au capped inorganic titanium oxide TiO₂ nanocomposite in electroluminescent polymer and fabricated HPLED. We achieved enhanced optical properties of the device and the increased performance of the HPLED is attributed from the electronic charge transport properties of Au capped metal oxide particles in the electroluminescence polymer. The interfacial contact area of electroluminescence polymer and cathode increased by the incorporated nanoparticles in the organic polymer phase thereby improved luminescence properties.