This PDF file contains the front matter associated with SPIE Proceedings Volume 6486, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The fundamental mechanisms of electroluminescence (EL) refrigeration in heterostructure light emitting diodes, is examined via carrier energy loss (and gain) during transport, relaxation, and recombination, where the contribution of electrons and holes are treated separately. This analysis shows that the EL refrigeration process is a combination of thermoelectric cooling that mainly occurs near the metal/semiconductor contacts and radiative recombination which mainly occurs in the active region. In semiconductors such as GaAs, electrons and holes make different contributions to the refrigeration processes as a result of their different densities of states.

This paper presents a new method of designing binary optical structures to improve light extraction efficiency for emitters. Using this method a novel binary optical structure is generated. Such structures with an approximate width of 300 nm, are non-period and small enough in size so that they do not generate diffraction orders other than the zero order. They are also insensitive to polarization. They serve as an antireflection layer, sending light outward that would otherwise be absorbed within the device. The experimental devices were GaN based LEDs emitting at 460nm. The non-periodic binary structures and some periodic structures such as triangle-lattice Photonic Crystals (PC), 12-fold Quasi-periodic Photonic Crystals (QPC) are fabricated on the same sapphire side of a LED's flip chip with a Focus Ion Beam (FIB) for comparison. The surface profile of the structures was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Near field scanning optical microscopy (NSOM) was used to measure the output spectral properties of the devices. Electrical Luminescence (EL) measurements show that the greatest enhancement of emission light intensity was achieved in non-periodic binary structures. This increase was 60~135% at room temperature. It demonstrates that this Non-Periodic Binary Optical Structures will be useful for fabricating high efficient GaN-based LED.

A GaInN light-emitting diode (LED) that employs a new type of reflector consisting of an array of SiO₂ pyramids and a reflective Ag layer is demonstrated to have enhanced light extraction compared to GaInN LEDs with a planar Ag reflector. Ray tracing simulations reveal that the pyramid reflector provides 14.1% enhancement in extraction efficiency. Consistent with the simulation, it is experimentally demonstrated that the GaInN LED employing the pyramid-patterned Ag reflector shows 13.9% higher light-output compared to the LED with a planar Ag reflector. In addition, the GaInN LED with pyramid reflector shows uniform light intensity due to current spreading beneath the SiO₂ pyramid pattern. The enhancement is attributed to the appearance of an additional escape cone for light extraction, enabled by the change in direction of light rays reflected by the 3-dimensional pyramid reflector.

A ceramic THS solder mounts a broad, regular field of LEDs and the electronics. To collect the lateral emissions, each LED seats on a thermal riser, at a focus of its primary mirror. If parabolic, the mirrors deliver collimated beams. If elliptical, each mirror focuses on a delivery FO, or on a phosphor dot placed inside the window or tipping the FO. The sealing window can integrate other lenses to complete this compact, self-cooled, hermetic light-emitting engine.

High-brightness LEDs are compound semiconductor devices and distinguish themselves from conventional LEDs by their exceptional luminosity. Today they are increasingly used as light sources, replacing conventional incandescent and fluorescent lamp technologies. HB LEDs are difficult to manufacture, as they must be grown by sophisticated epitaxial growth techniques such as MOCVD. They are packaged like power semiconductors, using surface mount technology and thermal pads. After having been successfully applied to GaN scribing for side-emitting LEDs, the Laser MicroJet^(R) is used today for cutting heat sinks of HB white LEDs. Due to the high-emitted light power, the generated heat must be dissipated through a heat sink. Materials typically employed are metals with high heat conductivity, notably CuW and molybdenum. Applying the Laser MicroJet^(R) the achieved cutting quality in these metals is outstanding - smooth edges, no contamination, no burrs, no heat damage, no warping - all this at high speed.

Displays based on organic light-emitting diodes (OLED) have rapidly developed and are commercially available since some time. However, in order to achieve large market penetration in new segments like lighting and optoelectronic, it is generally expected that the current status of the field has to advance in terms of manufacturing cost and integration possibilities. OLED devices with electrically doped transport layers show low operating voltage, high efficiency and long lifetime. In this paper we demonstrate that the concept of p- and n-type electrical doping can be applied under manufacturing conditions on the worldwide first vertical in-line fabrication setup for large area lighting applications. An in-linemanufactured highly efficient white-OLED-system will be presented. The driving of large area lighting tiles defines the resulting OLED lifetime and efficiency. In this paper we will present first results on the driving of large area lighting panels. Beside the lighting application the integration of highly efficient OLEDs for optoelectronic applications is an opportunity for innovative new applications. Microdisplays, integrated optocoupler and light barriers are few examples for the potential of OLEDs in optoelectronic applications. We will present results regarding the integration of highly efficient top-emitting PIN OLEDs^TM for optoelectronic applications.

By introducing a solution-based titanium oxide (TiO_x) layer between the polymer and Al electrode in polymer lightemitting diodes, we have demonstrated that the devices exhibit an enhanced efficiency. The TiO_x layer reduces the barrier height between the polymer and Al cathode, thereby facilitating the electron injection in the devices and enhancing the device performance by achieving a balance of charge injection and transport between the electrons and holes. Moreover, we also believe that the TiO_x layers prevent the diffusion of metal ions into the emitting polymers during the Al deposition process, and reduce the degree of quenching centers in the active polymers.

"Optical Technologies have conquered the world" - their economic key data showed an impressive growth in the past couple of years, and the predictions for the up-coming years keep the expectations high^{1, 2}. In the case of OLED (Organic Light Emitting Diode) lighting, e.g. IDTechEx is predicting a worldwide market growth from 50 million USD in 2009 to 3.3 billion USD in 2012³. LED and OLED technology, although both being referred to as solid state lighting, are rather complementary in their characteristics. Whereas LEDs are high efficient point light sources, OLEDs cover large area, diffuse lighting applications which can follow the increased awareness for creation of personalized atmosphere. Ambience and mood lighting can be perfectly realized by the means of OLED large area illumination which will pave the way for applications that up to now could not have been realized. OLED lighting technology rests on three pillars at the same time, the basic performance like efficiency and lifetime, the unique features, and costs. These key challenges and their impact on various applications will be discussed.

Compared to established LCD and plasma technologies displays based on organic light emitting diodes (OLEDs) promise more brilliant images, less energy consumption and lower production costs. Furthermore, the organic layers that make up an OLED can be engineered to be transparent in the visible part of the spectrum. In combination with transparent conductive oxides like Indium-Tin-Oxide (ITO) or Aluminum doped Zinc-Oxide (AZO) as contacts OLEDs may be built entirely transparent. One major issue to be addressed in the fabrication of these devices is the deposition of the top transparent contact without damaging the organic layers. Transparent OLED pixels can be arranged to form entirely transparent OLED displays. For the active matrix addressing of the individual OLED pixels, we use TFTs which are transparent themselves. Rather than silicon, they are based on the wide-bandgap semiconductor Zinc-Tin-Oxide (ZTO) and transmit about 80 % of the visible light (400-750 nm). The transistors typically have field-effect mobilities of 13 cm²/Vs (an order of magnitude larger than a-Si TFTs) and an on-off ratio of 10⁶. The OLED pixel which needs to be driven may be positioned directly on top of the driver circuit. The pixels fabricated accordingly have an overall transmittance > 70 % in the visible spectrum. The brightness of the OLED pixels could be varied from 0 to 700 cd/m² via the gate bias of the driving TFTs. These devices state the initial building blocks of future, large-area, high-resolution transparent OLED displays. More complex transparent driving circuits, required to compensate eventual device variations will be discussed.

Polymer light emitting diodes (PLEDs) have been fabricated in a vacuum environment by resonant infrared laser ablation of the light emitting layer. The light emitting polymer used was poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and was deposited into the device structure ITO/MEH-PPV/Al. Fourier transform infrared (FTIR) spectroscopy confirmed that the laser-deposited polymer was not drastically altered by the deposition process. Laser-fabricated devices displayed similar properties such as electroluminescence spectra and IV characteristics as conventional spin-coated devices. The dependence of these device properties on laser fluence was investigated, and showed no strong dependency. Peak emission wavelengths of electroluminescence spectra were all within 10 nm of electroluminescence spectra of spin coated devices and showed only slight peak broadening. These results are technologically important in that shadow mask technology can be incorporated into this method to arbitrarily pattern substrates with light emitting polymers.

We present simulation and experimental results to achieve increased light extraction of a substrate emitting OLED. We present a comparison between a grating surface on the OLED and an array of microlenses at the interface between substrate and air. This experimentally gives -in both cases- a relative improvement of approx. 30 %. We also demonstrate the concept of a RC²LED, applied to an OLED. The RC²LED is composed by adding a high, low and high index layers between ITO and glass, i.e. the interface between organic layers and glass. These extra layers create a cavity which numerically gives a relative improvement of over 60% at the resonance wavelength of the cavity over a wavelength range of 50-100 nm. The influence of an array of micro lenses in addition to the RC² layers is also investigated in this paper.

The internal quantum efficiency as a function of the internal electric field was studied in InGaN/GaN based quantumwell heterostructures. Most striking, we find the IQE to be independent of the electron hole overlap for a standard green-emitting single quantum-well LED structure. In standard c-plane grown InGaN quantum wells, internal piezo-fields are responsible for a reduced overlap of electron and hole wavefunction. Minimization of these fields, for example by growth on non-polar m- and a-planes, is generally considered a key to improve the performance of nitride-based light emitting devices. In our experiment, we manipulate the overlap by applying different bias voltages to the standard c-plane grown sample, thus superimposing a voltage induced band-bending to the internal fields. In contrast to the IQE measurement, the dependence of carrier lifetime and wavelength shift on bias voltage could be explained solely by the internal piezo-fields according to the quantum confined Stark effect. Measurements were performed using temperature and bias dependent resonant photoluminescence, measuring luminescence and photocurrent simultaneously. Furthermore, the doping profile in the immediate vicinity of the QWs was found to be a key parameter that strongly influences the IQE measurement. A doping induced intrinsic hole reservoir inside the QWs is suggested to enhance the radiative exciton recombination rate and thus to improve saturation of photoluminescence efficiency.

Light-emitting diodes (LEDs) have been recognized as a generation of new light sources because they possess the properties of energy-saving, environmental protection, long lifetime, and those lacking in conventional lighting. To satisfy the requirements for different applications (e.g., for large-scale displays), determining the spatial radiances of LEDs is important to identifying their viewing angle and utilizing their lighting efficiency. The objective of this paper is to build up a real-time spatial radiance measurement system for LEDs, on the basis of digital signal processing (DSP) techniques. In this paper, the system analysis is given to show the feasibility of this work. Two primary subsystems are devised to perform the real-time measurements. First, in the optoelectronic sensing and signal processing subsystem, a wide-bandwidth photodiode sensing circuit is employed to acquire optical signals at a high speed, and an automatic gain control (AGC) circuit is designed to increase the measurement range. To support high-speed data processing, a DSP-based platform is developed in the subsystem. Second, a light-source rotation scheme is used in the optomechanical subsystem. For performance evaluations, we adopt a standard calibrating light source to test and verify our system. Experimental results indicate that the proposed system gives satisfactory results.

Light-emitting diodes (LEDs) degradation during 10 000 hours and the influence of ultrasonic action on the InGaN LEDs were investigated. The model of LED degradation is suggested and based on 1) common LED is the combination of parallel Small-LEDs (S-LED) which correspond to the areas with different concentration of In atoms; 2) redistribution of In atoms in quantum-dimensional active region of blue InGaN LED under strong piezoelectric effect and spontaneous polarization induced by ultrasonics; 3) the ultrasonics which is used in creating LEDs can make defects in heterostructures and they (during LEDs work) are heated by current or ultrasonic, can be increased and that's why nonradiation recombination decreases LEDs efficiency. It can be said that great current density flows through areas with low In concentration and therefore S-LEDs are "burned out" and irradiate less. At the areas with average In concentration the densities decrease. That is why electroluminescence spectrum, radiation power, luminous intensity characteristics are shifted to the long wave region. All that also exactly corresponds with our experimental results of LEDs degradation investigation during 10 000 hours.

In this paper, a current-accelerated method for fast estimation of the intensity and color degradation with corresponding variability of light-emitting diodes (LEDs) is presented. The method is based on automated periodical spectral measurements of emitted light of LEDs under different current loads, which include nominal and several different above nominal currents. The intensity and color degradation and corresponding variability among different LEDs at a specified current are estimated by detailed analysis of the acquired spectral data at above nominal currents. The method was validated by comparing the predicted values with the measured values at nominal current. The proposed method was tested on white LEDs (luminous intensity ranged from 5 to 20 cd) from five manufacturers (Nichia, Etgtech, Sansen, Daina, and Velleman). The results show that the intensity and color degradation and corresponding variability among different LEDs is significant and, therefore, should be considered with great care when designing highly demanding lighting products.

A study has been conducted to determine the effects of mechanical stresses induced from the coefficient of thermal expansion (CTE) differential between a light emitting diode (LED) chip, and various substrate materials to which the LEDs were mounted. The LEDs were bonded to typical packaging materials including ceramics, copper and metal matrix composites. The objective of this investigation was to determine the viability of implementing alternate substrate materials for packaging of LED power chips. In particular, thermally induced stresses resulting from the CTE differentials between the alternate substrate materials and the LED sub-mount material were analyzed and compared against the stresses resulting from the nearly ideal CTE match that is realized with traditional ceramic substrates.

The Step and Flash Imprint Lithography (S-FIL™) process is a nano-imprint lithography technique based on UV curable low viscosity liquids. S-FIL uses drop dispensing of UV curable liquids to pattern entire wafers with a single imprint. This approach allows for micro and nano-fabrication of devices with widely varying pattern densities and complicated structures over wafers with high nanotopography. Patterning of arbitrarily shaped sub-100 nm structures with nanotopography which is greater than 10&mgr;m is not obtainable using DUV stepper technology. Photonic crystal structures, wire grid polarizers and micro lenses are examples of optical components that can be formed using S-FIL technology imprinting on whole substrates. The authors have devised a beginning to end lithography process which includes: wafer preparation processes for imprint, a high throughput whole wafer step and repeat imprint process and dry etching processes for resists and hard mask patterning. The process is capable of patterning sub-100 nm hard masks on substrates where the nanotopography is in excess of 10&mgr;m across the substrate. The imprint process flow uses the Step and Flash Imprint Lithography Reverse (S-FIL/R) tone process which has been demonstrated to be robust at holding critical dimensions for a wide window of etch conditions, wafer topography and defects. The authors describe a photonic crystal patterning process from beginning to end with particular attention to etch selectivity, analysis of cross wafer critical dimensions and a survey of defect requirements for successful high yield imprint patterning.

In this paper we investigate improvement in performance attainable by etching Photonic Crystals and Photonic Quasi-Crystals into the top emitting surface of LEDs. We describe the physical mechanisms of extraction enhancement through ordered surface patterning and investigate benefits in terms of total extraction enhancement, beam directionality, and far field beam quality. Factors such as lattice geometry, etch depth, and epitaxy thickness are investigated. We show that a great variety of far field beam profiles of benefit in applications such as projection TV light engines and direct flat panel display illumination can be obtained simply by adjusting geometric design parameters. Our results show that PCs can provide significant improvement in extraction enhancement for applications requiring non Lambertian beam shapes when etched into standard "production line" epitaxy wafers in comparison to "state of the art" surface roughened thin-GaN LED devices. We investigate PC beam steering effects in these devices confirming that PCs do in fact re-direct light from trapped modes confined within the epi-structure to radiating modes. We also show that by tailoring the thickness of the epi-structure to complement the properties of the photonic crystal, extraction enhancement can be improved by a factor of 9 for some applications.

We extended the theory by Henry [1] to accurately treat the coupling of spontaneous emission noise with microcavity modes. The Green's function method is employed to solve the inhomogeneous wave equation including a Langevin force f_&comega; which accounts for spontaneous emission by carriers at angular frequency &comega;. The optical wave equation is coupled with the self-consistent calculations of the material spontaneous emission rate of quantum well/dot using envelope wavefunction method. Finally the carrier transport equations are solved within the framework of 2D/3D drift-diffusion model implemented in the Crosslight Software package APSYS [2]. The simulation results of a GaN based resonant-cavity light-emitting diode (RC-LED) showed that our models can be used to predict the characteristics of RC-LED.

We report new capabilities in our Sentaurus-Device¹ simulator for modeling arbitrarily shaped 2D/3D white LEDs by coupling novel photon recycling, luminescent spectral conversion effects and electrical transport self consistently. In our simulator, the spontaneous emission spectra are embedded in ray tracing, and are allowed to evolve as the rays traverse regions of stimulated gain, absorption, and luminescence. In the active quantum well (QW), the spontaneous emission spectrum can be partially amplified by stimulated gain within a certain energy range and absorbed at higher energies, resulting in a modified spontaneous spectrum. The amplified and absorbed parts of the spectrum give a net recombination/generation rate that is feedback to the electrical transport via the continuity equations. This conceives a novel photon recycling model that includes amplified spontaneous emission. The modified spontaneous spectrum can further be altered by spectral conversion in the luminescent region. In this manner, we capture the important physical effects in white LED structures in a fully coupled and self-consistent electro-opto-thermal simulation.

This paper illustrates how technology computer-aided design (TCAD), which nowadays is an essential part of CMOS technology, can be applied to LED development and manufacturing. In the first part, the essential electrical and optical models inherent to LED modeling are reviewed. The second part of the work describes a methodology to improve the efficiency of the simulation procedure by using the concept of process compact models (PCMs). The last part demonstrates the capabilities of PCMs using an example of a blue InGaN LED. In particular, a parameter screening is performed to find the most important parameters, an optimization task incorporating the robustness of the design is carried out, and finally the impact of manufacturing tolerances on yield is investigated. It is indicated how the concept of PCMs can contribute to an efficient design for manufacturing DFM-aware development.

The measurement of the bias and temperature dependent photoluminescence, photocurrent and their decay times allows to deduce important physical properties such as barrier height, electron-hole overlap and the magnitude of the piezoelectric field in InGaN quantum wells. However the analysis of these experiments demands for a detailed physical model based on a realistic device structure which is able to predict the measured quantities. In this work a selfconsistent model is presented based on a realistic description of the alloy and doping profile of a green InGaN single quantum well light emitting diode. The model succeeds in the quantitative prediction of the quantum confined Stark shift and the associated change in the electron-hole overlap measured via the change in the bimolecular decay rate using literature parameters for the piezoelectric constants. The blue shift of the emission under forward current conditions can be attributed to the carrier induced screening of the piezoelectric charges as predicted by the model. The photocurrent is calculated via thermionic tunneling through the barriers using a WKB-approximation and the calculated potential profile for the tunneling barrier. From the fact that the bias and temperature dependence of the experimentally observed photocurrent cannot be described by the thermionic tunneling model even though the theoretical potential profile fits excellent to the luminescence data, we conclude that the carrier escape is dominated by a different mechanism such as defect- or phonon-assisted tunneling.

Light emitting Diodes (LEDs) which use phosphor conversion might be a neat alternative to the more costly 3 chip RGB (red, green, blue) LEDs. Almost any color of phosphor conversion LEDs (pc-LEDs) can be adjusted by combining a light-emitting semiconductor chip and one or more phosphors. Depending on the ratio of unconverted and converted light, it is possible to verify both unsaturated and saturated colors. A very common type of phosphor conversion LED is composed of a reflector cavity, which contains a blue light emitting chip and is filled by a phosphor containing resin. At a fixed concentration, parameters like the thickness of the phosphor filled resin layer (conversion layer) above the chip and the wavelength influence the final color of the pc-LED. It is necessary to reduce the variation of the influencing parameters to be able to control the color and prevent yield losses in the production. A new phosphor coating technique developed at OSRAM OS makes it possible to precisely control the thickness of the conversion layer above the chip. A layer of a hard resin is applied on top of a wafer and afterwards its thickness is milled accurately to the desired value. With this new technique the color distribution can be reduced significantly compared to the common techniques.

Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools and detection methods for product and process control, material sciences, environmental and bio-technical analysis, molecular genetics, cell biology, medical diagnostics and drug screening. According to DIN/ISO 17025 certified standards are used for fluorescence diagnostics having the drawback of giving relative values for fluorescence intensities only. Therefore reference materials for a quantitative characterization have to be related directly to the materials under investigation. In order to evaluate these figures it is necessary to calculate absolute numbers like absorption/excitation cross section and quantum yield. This can be done for different types of dopants in different materials like glass, glass ceramics, crystals or nano crystalline material embedded in polymer matrices. Here we consider a special type of glass ceramic with Ce doped YAG as the main crystalline phase. This material has been developed for the generation of white light realized by a blue 460 nm semiconductor transition using a yellow phosphor or converter material respectively. Our glass ceramic is a pure solid state solution for a yellow phosphor. For the production of such a kind of material a well controlled thermal treatment is employed to transfer the original glass into a glass ceramic with a specific crystalline phase. In our material Ce doped YAG crystallites of a size of several µm are embedded in a matrix of a residual glass. We present chemical, structural and spectroscopic properties of our material. Based on this we will discuss design options for white LED's with respect to heat management, scattering regime, reflection losses, chemical durability and stability against blue and UV radiation, which evolve from our recently developed material. In this paper we present first results on our approaches to evaluate quantum yield and light output. Used diagnostics are fluorescence (steady state, decay time) and absorption (remission, absorption) spectroscopy working in different temperature regimes (10 - 350 K) of the measured samples in order to get a microscopic view of the relevant physical processes and to prove the correctness of the obtained data.

The use of LEDs in advanced optical systems such as LED projectors or automotive headlamps is usually limited by the optical extend of the light source. The optical extend (or étendue) is defined as the product of the optical area and the divergence angle of the emission. In our paper, we discuss the consequences of such limitations on the design and performance of optical systems. The system optimization involves the chip technology, package design and the primary optics, producing an optical extend that has to match with the optical extend of the imager component. It will be shown how these optical laws put constraints on the LED light source and the design of suitable light engines. The benefits of LED light sources for the above mentioned applications will also be demonstrated.

We have for the first time developed warm white LEDs lighting using a combination of near ultraviolet LED and three-band (red, green and blue) white phosphors. This LED has the average color-rendering index Ra=96. Moreover, special color-rendering index R9 (red) and R15 (face color of Japanese) are estimated to be 95 and 97, respectively. We will describe the results of evaluation on the medical lighting applications such as operation, treatment and endoscope experiments, application to the LED fashions and application to the Japanese antique art (ink painting) lighting.

The luminaires utilizing high power LED are prevailing for general use. In the application, multiple numbers of LED are required to attain the desired brightness. It is important to control the light distribution to combine the luminous flux from each LED. We designed and fabricated the luminaire to control the luminous flux of the LEDs and succeeded to obtain the designed uniform light distribution with small deviation of chromaticity.

Trichromatic LED backlights render higher color gamut and panel transmittance to liquid crystal displays (LCDs) than yellow phosphor-converted white LED backlights can possibly do at their best. In realization, however, several technical challenges arise, such as colour shift due to the ambient temperature change, decrease in brightness at elevated temperature, an enlarged dead zone for colour mixing, minimizing the total number of chips and so on. In this work, we designed and demonstrated a low-cost driving circuit that stabilizes brightness and colour coordinates of trichromatic LED backlights using a thermistor as a temperature compensating element. By applying the temperature compensation, the amounts of the brightness and colour shift were reduced to 54% and 51% of the uncompensated cases, respectively.

White light emitting diodes (LEDs) have been successfully fabricated for the first time in silicon carbide substrates (4H-SiC) using a novel laser doping technique. The donor-acceptor pair (DAP) recombination mechanism for luminescence has been used to tailor these LEDs. Chromium (Cr), which produces multiple acceptor sites per atom, and selenium which produces multiple donor sites per atom were successfully incorporated into SiC for the first time using laser doping. Aluminum (Al) and nitrogen (N) were also laser-doped into SiC. Green (521-575 nm) and blue (460-498 nm) wavelengths were observed due to radiative recombination transitions between donor-acceptors pairs of N-Cr and N-Al respectively, while a prominent violet (408 nm) wavelength was observed due to transitions from the nitrogen level to the valence band level. The red (698-738 nm) luminescence was mainly due to nitrogen excitons and other defect levels. This RGB combination produced a broadband white light spectrum extending from 380 to 900 nm. The color space tri-stimulus values were X = 0.3322, Y = 0.3320 and Z = 0.3358 as per 1931 CIE (International Commission on Illumination) for 4H-SiC corresponding to a color rendering index of 96.56; the color temperature of 5510 K is very close to average daylight (5500 K).

Energy levels and wave functions of ground and excited states of an exciton are calculated by the method of imaginary time. Energy levels as functions of radius of single and double wall nanotube are studied. Asymptotic behavior of energy levels at large and small values of the radius using perturbation theory and adiabatic approximation is considered. Spatially indirect exciton in semiconductor nanowire is also investigated. Experimental result from high quality reproducible ZnO nanowires grown by low temperature chemical engineering is presented. State of the art high brightness white light emitting diodes (HB-LEDs) are demonstrated from the grown ZnO nano-wires. The color temperature and color rendering index (CRI) of the HB-LEDs values was found to be (3250 K, 82), and (14000 K, 93), for the best LEDs, which means that the quality of light is superior to one obtained from GaN LEDs available on the market today. The role of V_Zn and V_O on the emission responsible for the white light band as well as the peak position of this important wide band is thoroughly investigated in a systematic way.

Thermal management is now a critical problem for applications of high power light emitting diodes (LEDs). This paper develops a novel LEDs (Fig.1a) package technique that can overcome thermal problem, and the ability to drive the red LEDs at higher power. Copper is plated on the AlInGaP-based red LED chip directly, and the thermal resistance from chip to the metal heat sink is decreased greatly. With the copper plating layer, the working current of the AlInGaP-based red LED can be increased from conventional 350 mA to 1650mA in room temperature. It was found that the luminous intensity at 350 and 1050 mA of the novel package LEDs showed 53% and 431% enhancement as compared with those of the conventional package ones (Fig.1b). The electrical and optical characteristics of two kind's packages were shown in Figure 2 and Figure 3, respectively.

We report a high-power light-emitting diode (LED) scheme based on aluminum (Al) reflector, commonly used as an n-GaN ohmic contact. The Cu doped In₂O₃ (5nm)/ITO (380nm) interlayer was deposited by electron beam evaporator and subsequently annealed at 500°C After annealing, we sputtered Al (400nm thick)/Ti-W (30nm) on the ITO interlayer to reflect the visible light. From the systematic experiment and the following analyses with InGaN/GaN multiple- quantum-well (MQW) LEDs, the reflectance of electrode based Al was measured to be ~ 90% at a wavelength of 450nm, which is higher than that of the common used Ni/Ag/Pt scheme. The forward- bias voltages of CIO/ITO/Al/Ti-W pelectrodes were as low as 3.2-3.3V. Furthermore, Al reflector showed higher thermal stability and lower leakage currents than those of typical Ag reflector, in which the mean leakage current of Ni/Ag and CIO/ITO/Al/Ti-W contacts were estimated to be 0.54, 0.12uA at an injection current of -5V, respectively.

It has been proved that monochromatic or compound light-emitting diode (LED) or laser diode (LD) can promote the photosynthesis of horticultural crops, but the promotion of polychromatic light like white LED is unclear. A new type of ultra-bright white LED (LUW56843, InGaN, &nullset; 5 mm, 150mW, 15000 mcd, wavelength range: 400~720 nm) was selected to make up of the supplemental lighting panel (200×300 mm²), on which LEDs were evenly distributed with 90 branches. Drive circuit was selected to power and adjust light intensity. System performance including temperature rise and light intensity under different currents and vertical distances were tested. Photosynthesis of sweet pepper and eggplant leaf under white LED was measured with LI-6400 to show the supplemental lighting effects. The results show that LED system can supply the maximum light intensity of 300 &mgr;mol/m² .s at the distance of 100 mm below the panel and the temperature rise is higher over 13 °C on the surface of LED encapsulation, but hardly changes 100 mm far away the panel. For both of the two vegetables net photosynthetic rate became faster when white LED system increased light intensity. Compared with sunlight and plant growth fluorescent lamp, white LED's promotion on photosynthesis is inferior because its spectra is unreasonable with more blue light and less red light. Therefore, the unreasonable spectra become the major constraint of its application, but the potential of white LED application into vegetable crop production is prospective.

We propose a large parallax barrier by use of aperture grille. Main advantages of using aperture grille include no reflection and no absorption in apertures. We have measured viewing areas around the main lobe and around side lobes. Experimental results show use of aperture grille increases contrast and enlarge the viewing areas compared to the conventional parallax barrier by use of a painted acrylic board. Furthermore, we have realized a large stereoscopic display by use of 140-inch LED panel.

TiO₂ nanoparticle-loaded epoxy for light-emitting diode (LED) encapsulation is demonstrated to have a refractive index of n = 1.68, higher than that of pure epoxy (n = 1.53). The dispersion of surfactant-coated TiO₂ nanoparticles into epoxy is shown to reduce the number and size of TiO₂ agglomerates compared to uncoated TiO₂ nanoparticle-loaded epoxy. The scattering of nanoparticle-loaded media is highly dependent on nanoparticle size and loading factor. A multilayer graded refractive index structure for LED encapsulants with layer thicknesses less than the calculated mean optical scattering length is therefore proposed. The graded-index structure shows increasing optical transmittance as the number of layers increases.