The automotive optical engineer has an entirely new set of rules to follow for a 'smooth lighted appearance' with the introduction of LEDs into the automotive signal lighting market. To move away from the 'polka-dot' appearance long associated with the usage of LEDs as the light source for automotive lighting, and give the consumer a smooth lighted appearance to his lamp, there are several optical parameters that must be observed. The number and type of LEDs used, the size of the optical elements used, the spacing of the optical elements, plus many other factors all play a critical role and must be considered in the solution to the 'smooth lighted appearance' in an automotive signal lamp. The 'smooth lighted appearance' in an automotive signal lamp has long been a difficult problem to which there is more than one solution. The most visually pleasing and effective solution is not always the most easily obtainable solution since photometry requirements and smooth lighted appearance can be diametric goals. Subsequently the most cost effective and the easily 'doable' solution may not give the ultimate in aesthetically pleasing results for the consumer. Therefore, it is the purpose and intent of this paper to outline the parameters that need to be considered to obtain a 'smooth lighted appearance' for an automotive signal lamp, and to clarify the methods and 'tools' that are required to meet this goal.

We describe the lighting characteristics and systems of the power energy-saving type street lamp which consists of white light-emitting diodes (LEDs), and a solar-cell and battery system. The prototype street lamp has been constructed by two LED light sources, each of which includes a total of 700 units of 10 cd-class white LEDs. The white LED lighting system is mainly divided into three components which are the control, the electric-power supply and LED lighting divisions. The illuminance is normally 80 lx. When a person approaches within 2 m near the lamp, the body sensor catches the situation. The illuminance then increases to about 660 lx, which is about 50 times brighter than that of a white incandescent lamp. The color rendering index is estimated to be 85 which is similar to that of three color fluorescent tube. The illuminance distribution can be analyzed by our recently developed 'multi sources of LED light' theory.

There is a large number of new applications in lighting and display technology where high-brightness AlGaInP-LEDs can provide cost-efficient solutions for the red to yellow color range. Osram Opto Semiconductors has developed a new generation of MOVPE-grown AlInGaP-LEDs to meet these demands. Our structures use optimized epitaxial layer design, improved contact geometry and a new type of surface texturing. Based on this technology we achieve luminous efficiencies of more than 30 lm/W and wallplug efficiencies exceeding 10% of LEDs on absorbing GaAs substrates. The epitaxial structure does not require the growth of extremely thick window layer and standard processes are used for the chip fabrication. This allows for high production yields and cost-efficient production.

In such LED applications as lighting, it is desirable to have the highest light output for the lowest power consumption. This paper investigates the optical properties and electronic requirements of a commercially available yellow LED as a function of temperature from ambient to liquid nitrogen temperatures. It was found that the illuminance increased by almost an order of magnitude, producing much higher light output at the same diode current. However, the operating voltage increased, increasing the overall power consumption slightly. The efficiency (light-watt output to electrical watts consumed) of the LED, though, improved by a factor of more than three. This, combined with the enhanced light output, compensates for the small increase in power consumption and added cooling costs. These improvements further translate into a comparable increase in the lifetime of the LEDs. In general, each ten-degree reduction in temperature corresponds to a doubling of the lifetime of semiconductor devices. It was also found that the maximum operating current increased significantly at liquid nitrogen temperatures over that at ambient temperatures. Lastly, the emitted wavelength range shifted to shorter values in addition to the significant increase in brightness. Thus, a yellow- colored LED at room temperature gave off a much brighter yellow-green-white color at liquid nitrogen temperatures.

The external quantum efficiency of planar light-emitting diodes (LED's) can be increased significantly by the approach of a non-resonant cavity (NRC) LED, which consists of texturing the top surface and applying a rear reflector. We demonstrate this approach for the first time on 650-nm InGaP/AlInGaP LED's. The LED's are fabricated using the processing techniques developed previously for 860-nm GaAs/AlGaAs NRC-LED's, which include wet thermal oxidation for the formation of a current aperture. With un-encapsulated NRC- LED's, we report an external quantum efficiency of 24% for an emission wavelength of 655 nm. This is an 11-fold increase of the external quantum efficiency, as compared to conventional devices. Furthermore, the efficiency is demonstrated to increase to 31% by on-wafer encapsulation of the LED's. This results in an optical output power of 4 mW for a drive current of 7 mA.

Usually resonant-cavity light-emitting diodes (RCLEDs) are used as emitters for plastic optical fiber communication. However, there are some arguments that may lead to the introduction of RCLEDs in a much wider range of applications. A typical high-brightness AlGaInP LED consists of a Bragg mirror, the active region and some layers for current spreading and light extraction. The thickness of these layers can add up to several ten microns which causes long epitaxial growth times. The total thickness of a RCLED can be significantly lower. Furthermore, since no lattice mismatched layers such as GaP are involved, the total incorporated strain is low which simplifies wafer handling and device processing. For this reason we studied RCLEDs with a dominant wavelength around 632 nm (superred) and 605 nm (orange). The processes for epitaxial growth and chip fabrication were optimized for homogeneity on 4 inch wafers and suitability for low-cost mass production, respectively. Possible applications for our RCLEDs are optical scanners, indicators, signal lights and other applications which benefit from the enhanced directionality of RCLEDs.

State of the art resonant microcavity light emitting diodes (RC-LEDs) for the red wavelength range are presented in the paper. Our red-emitting RC-LEDs were mainly intended for low- cost short-haul communication systems on polymethyl methacrylate plastic optical fiber (POF) but the devices provide viable alternatives for conventional LEDs or for VCSELs in applications where moderate spectral purity, moderate bandwidth and low-cost are required. The paper discusses the design concepts, fabrication issues and performance characteristics of monolithic RC-LEDs' emission is centered in the 650 - 655 nm range, which corresponds to the PMMA POF transmission window, and has a spectral linewidth below 15 nm. The RC-LEDs with 500 micrometer diameter windows launch 15 mW of light power. Smaller 40 micrometer devices are very fast exhibiting f_-3dB up to 350 MHz at reasonable power levels. The 84 micrometer devices achieve a record external quantum efficiency of 9.5% and a back-to-back error- free data transmission rate beyond 622 Mbit/s. Alignment tests with 1 mm POF fibers, without lenses, showed that +/- 0.5 mm misalignment might be tolerated in x-y-z directions without significant reduction in coupling efficiency. The devices appear to be very robust, neither sudden unexpected failure nor gradual power degradation has been observed during more than 93000 device hours on accelerated aging tests.

Detailed study of external quantum efficiency (eta) _QE is reported for AlGaInP-based Microcavity Light-Emitting Diodes (MCLEDs). Unlike conventional LED's the extraction efficiency (gamma) _ext and far field profile depend on the linewidth of the intrinsic spontaneous emission and wavelength detuning between cavity mode and peak electroluminescence. This dependence makes it difficult to estimate the intrinsic spectrum, hence the performances of MCLED's. By using a non- destructive deconvolution technique, the intrinsic spectra of a MCLED and a reference LED (with the same active regions) could be determined at different current densities. This allowed precise calculation of (gamma) _ext for both devices (values close to 11% were found for the MCLED), hence of their apparent internal quantum efficiencies (eta) _int. At 55 A/cm², values of 90% and 40% were determined for the LED and MCLED respectively. In order to explain this difference, we measured (eta) _QE for devices with different sizes. From a fitting procedure based on a simple model taking into account the device size, we found out that the radiative efficiencies of LEDs and MCLEDs were close to 90%. We concluded that the low (eta) _int of MCLED was due to a bad current injection, and especially to electron leakage current, as confirmed by numerical simulations.

Microcavity light emitting diodes (MCLEDs) are planar emitting devices that can achieve large brightness increase compare to conventional LEDs. We designed and fabricated a GaAs/Al_xGa_1-xAs surface-emitting MCLED emitting at 880 nm. Two InGaAs quantum wells are included in a (lambda) -Al_0.3Ga_0.7As cavity between two Al_0.1Ga_0.9As/Al_0.8Ga_0.2As Bragg mirrors. The top n-doped Bragg mirror has 4 pairs, the bottom one is p-doped like the substrate and has 20 pairs. The detuning between the source emission wavelength and the Fabry Perot wavelength is -20 nm. It is optimum for an extraction into air. By inserting the bonded MCLED device into an integration sphere we measured a maximum external quantum efficiency of 14% at 10 mA. An epoxy lens is placed on top of the device and the external quantum efficiency is increased up to 20.5% at 10 mA. These values are in good agreement with theoretical calculations if the internal quantum efficiency of the structure is equal to 85%. Additional calculations and measurements are performed and lead to a good physical understanding of the MCLED.

We present results on Resonant Cavity Light Emitting Diodes (RCLEDs) emitting at 650 nm, which have high efficiencies and low voltages. In particular, we report on the angular properties of these devices, and highlight the observation that overall spectral linewidth increases with collection angle. This unusual property of RCLEDs is largely a consequence of employing a microcavity in the design. An additional contributing factor is the relative distribution of gain amongst the cavity modes (i.e. the level of tuning or detuning of the underlying emission, defined with respect to the longitudinal cavity mode). We have used measurement techniques which spectrally resolve angular radiation profiles to determine the (de)tuning directly. Moreover, these profiles demonstrate how the overall spectral linewidth increases with collection angle. To this end, we have developed a semi- empirical method for determining the overall linewidth as a function of emission numerical aperture (NA). A 4 nm detuned device has been investigated and linewidths have been found to increase from 3.1 nm to 13.6 nm over a range of NA approximately equals 0 to NA equals 1, an increase by a factor of around 4. Obviously, a variable linewidth also implies a variable coherence length with NA. Consequently, the coherence length was found to decrease from 30 micrometer to 9 micrometer over the same range. Independent coherence length measurements were carried out by direct interferometric measurements, and confirmed the expected trends.

Light-emitting diodes (LEDs) with high efficiencies can be fabricated by a combination of surface texturing and the application of a rear reflector. We demonstrate an external quantum efficiency of 43% for unencapsulated surface-textured thin-film LEDs, which increases to 54% after encapsulation. At low temperatures, the efficiency of unencapsulated devices increases up to 68%. We investigate the light extraction mechanism from such LEDs employing a Monte Carlo simulation of the light propagation inside the LED structure. One essential input parameter for the simulation are the light scattering properties of the textured surface, which have been investigated experimentally. For light incidence below the critical angle of total internal reflection, the transmission through a textured surface is reduced compared to a flat surface. However, due to surface texturing, transmission becomes possible for incident angles above the critical angle. As a result, the internal scattering during internal reflection at the textured surface is not necessary for an efficient extraction of the light generated inside the LED structure. In addition, the Monte Carlo simulation also explains the strong increase of the LED efficiency at low temperatures quantitatively by photon recycling effects. Photon recycling is also demonstrated to be partially responsible for the shift of the emission wavelength in thin- film LEDs, as compared to conventional LEDs.

In this presentation, basic elements of light-emitting diode (LED) lamp design are discussed. In practical applications of LED lamps, the far-field photon distribution pattern is one of the important considerations. Both the reflecting cup and lens surface profile employed in the design can be flexibly adjusted by a few parameters such that the far field photon distribution pattern is rather easily manipulated. For simulation of LED lamps, we have used Monte Carlo photon simulation method. Based on simulation results, we can verify or explain the effect of the various LED lamp design parameters on far-field patterns. Some of the important design examples are LED lamps with far-field patterns that are either tilted by certain angle in the vertical direction or double- lobed in the horizontal direction. LED lamps of this type of far-field patterns may find some application in some special outdoor displays, for instance, in a large stadium.

We have investigated efficient light outcoupling from light- emitting diodes (LEDs) by introducing lateral tapers. The concept is based on light generation in the very central area of a circularly symmetric structure. After propagating between two highly reflecting mirrors light is outcoupled in a tapered mesa region. By proper processing we achieve quantum efficiencies of almost 40% for outcoupling via a planar surface or quantum and wallplug efficiencies of 52% and 48%, respectively, for encapsulated devices. Neglecting reabsorption, approximative equations yield optimum design parameters.

The GaN-based multiple quantum wells (MQW) laser diodes have been improved excellently by introducing GaN/GaInN optical- guiding layers and by reducing dislocation density. The lifetime of continuous wave operation has been improved to longer than 300 hours with 3 mW at the wavelength of 409 nm.

High-power light-emitting diodes (LEDs) in both the AlInGaP (red to amber) and the AlGaInN (blue-green) material systems are now commercially available. These high-power LEDs enable applications wherein high flux is necessary, opening up new markets that previously required a large number of conventional LEDs. Data are presented on high-power AlGaInN LEDs utilizing flip-chip device structures. The high-power flip-chip LED is contained in a package that provides high current and temperature operation, high reliability, and optimized radiation patterns. These LEDs produce record powers of 350 mW (1A dc, 300 K) with low (<4V) forward voltages. The performance of these LEDs is demonstrated in terms of output power, efficiency, and electrical characteristics.

Current crowding in mesa-structure GaInN/GaN light-emitting diodes (LEDs) grown on insulating substrates is analyzed. A model developed reveals an exponential decrease of the current density with distance from the mesa edge. Devices with stripe- shaped mesa geometry display current crowding and a saturation of the optical output power at high injection currents. It is shown that the optical power saturation depends on the device geometry. It is also shown that saturation is less pronounced in LEDs employing a ring-shaped mesa geometry, which reduces current crowding, as compared to the conventional square- shaped mesa geometry.

This study invests the effect of barrier growth temperature on the properties of InGaN/GaN MQW. Increase the growth temperature will reduce the well thickness and result in the blue shift of the PL peak. This blue shift in PL peak wavelength may be resulted from the stain occur during varying barrier growth temperature rather than only the reduce the well width. Moreover, we introduce a phase separation enhance layer into InGaN/GaN MQW. This layer join with the variation of barrier growth temperature will enhance the phase separation in InGaN/GaN MQW. There are two peaks clearly revealed in RT PL spectra. The higher energy peak might originate the InGaN quasi-wetting layer on the GaN barrier surface. The other one is interpreted of localize state at potential fluctuation owning to phase separation.

Nonradiative dynamics of the carriers and/or excitons created by the photoexcitation in InGaN-based light emitting diodes (LEDs) with blue (460 nm, 470 nm), green (510 nm, 540 nm), and amber (600 nm) emissions were observed by using the transient grating (TG) method which is one of the third-order nonlinear spectroscopy. The dynamics of carries and/or exciton diffusion and dynamics of heat energy released by the nonradiative recombination were observed by the time profile of the TG signals in picosecond and nanosecond time region, respectively. The diffusion coefficients and the temperature change by the heat generation were detected for several LEDs and potted against the peak wavelengths of emission (In composition in active layers). Those results were compared with the results of the time-resolved photoluminescence (PL) spectroscopy. Dependence of In composition on the radiative and nonradiative recombination lifetimes, the luminescence intensities, the internal quantum efficiencies, the heat generation and conduction processes, and the diffusion coefficients of excitons and/or careers were interpreted by the model in terms of the fluctuation and phase separation of In composition.

We report results on the transferability of a blue-green electroluminescence test structure (ELT) process across different reactor geometries and substrate materials. The process was transferred from the conditions of our well-known 6 X 2 inch to the 5 X 3 inch AIX 2400 G3 geometry by simple up-scaling of the respective process parameters in accordance with numerical simulations done on the reactor setup. The five period InGaN/GaN quantum well ELT structures with an average emission wavelength on wafer of 480 nm shows a standard deviation of 1 - 2% without rim exclusion. Electroluminescence up to 560 nm were achieved in InGaN/GaN structures with high In content. With these prospects new types of seed layers for the transfer of our standard electroluminescence test structures (ELT) process to Si- substrates were investigated. The growth on different seed layers was found feasible and resulted in operational ELT structures with emission wavelengths in the range of 440 nm to 470 nm. Electrical quick test shows bright blue emission across the full Si wafer.

Everywhere in the world, the highest quality and quantity of lighting is required during the surgical operations. However, the surgical approach has had many types and various angles, common ceiling surgical halogen lighting system cannot provide an adequate amount of beams because the surgeons' heads hinder the illuminations from reaching the operation field. Here, we newly design surgical lighting system composed of white LEDs equipped on both sides of goggles, which controls the lighting beams to the gazing point. With this system, it is just needed for surgeons to wear light plastic goggles with high quality LEDs made by Nichia. In fact, we have succeeded in the first internal shunt operation in the left forearm using the surgical LED lighting system on 11th Sept 2000. The electrical power for the system was supplied from lithium-ion battery for 2 hours. Since the white LEDs used were composed of InGaN- blue-emitters and YAG-yellow-phosphors, the color rendering property was not sufficient in the reddish colors. Therefore, in the next approach, it is very important to develop the spectral distribution of white LED to render inherent color of raw flesh such as skin, blood, fat tissue and internal organs.

Organic electroluminescent devices using tris-(8-hydroxy) quinoline aluminum (Alq₃) as the emissive layer and N,N'- diphenyl-N,N' bis (3-methylphenyl)-[1-1'-biphenyl]-4-4'- diamine (TPD) as the conventional hole transport layer have been fabricated. We tried to explore the charge transport mechanisms in the OLED device by the studying of temperature dependent luminescence over the temperature range from 10 K to 300 K. We found that first, at lower applied voltage, two peaks have been observed in the quantum efficiency with temperature, and they are due to deep trap levels (high temperature regime) and shallow trap levels (low temperature regime). With increasing voltage, the high-temperature peak shifts toward lower temperature but no significant shift of the low-temperature peak is observed, and when the voltage is over 10 V, superposition of the peaks causes the apparent saturation in the low temperature regime of the quantum efficiency. Second, up to a certain temperature luminescence intensity decreases with decreasing temperature and then saturated in the low temperature region. The quantum efficiency increases with decreasing temperature and finally reaches to almost a constant value. Meanwhile we tried to use Frenkel exciton model to explain the luminescence behavior of the device.

Heterocyclic aromatic polymer poly(p- phenylenebenzobisthiazole), PBT, is a rigid-rod polymer having a fully conjugated backbone as well as excellent dimensional, thermo-oxidative, and solvent stabilities. A PBT polymer with intrinsic viscosity of 18.0 dL/g was dissolved in methanesulfonic acid or Lewis acid. The PBT solution was spin- coated, doctor-bladed or extruded for freestanding films or onto an indium-tin-oxide (ITO) substrate. The acid was removed via coagulation resulted in PBT films of about 80 nm in thickness on the ITO substrate as determined by scanning electron microscopy. X-ray scattering demonstrated that the extruded freestanding films were uniaxial while the others were isotropic without long-range order. Both temperature and excitation power dependences of the photoluminescence measurements were performed. The laser excitation power dependence of the emission intensity is fitted well with a bimolecular recombination model. Light-emitting devices were fabricated with a structure of Al(Mg)/PBT/ITO/glass, and gave out green-yellow light. A threshold voltage as low as 1 V was achieved. Electroluminescence spectra showed a blue-shift with increasing voltage, which is ascribed to the band-filling effect. Vibrational structure emerged in the photoluminescence spectra at low temperatures, and was observed in the electroluminescence spectra at high voltages, which gives a vibrational mode spacing of 186 meV for the lowest levels.

InAs, InSb compounds and InAs(Sb)(P), In(Ga)As(Sb) based heterostructures grown onto InAs substrate have been used as a 'phosphor' for the optically pumped light emitting diodes emitting in the mid-IR spectral range (3 divided by 7 micrometer) at room and above room temperatures. The pulse output of the LEDs composed of GaAs pumping LED ((eta) _ext equals 6 divided by 8%) and 2 divided by 20 micrometer thick mid-IR 'phosphor' joint together through a transparent 'glue' was as high as 40 divided by 500 (mu) W which is fairy close to the best reported values for 'cascade' and single quantum well diodes operating in a spontaneous mode.

Multimode pulse (P equals 1.56 W, I equals 9.5 A) and CW (P equals 160 mW, I equals 1 A) operation is reported at 77 K for the broad (w equals 200 micrometer) contact InGaAsSb(Gd)/InAsSbP diode lasers with (lambda) equals 3.0 divided by 3.3 micrometer. Narrow stripe lasers (w equals 20 micrometer) exhibited singlemode CW power as high as 18.7 and 9.3 mW at 77 and 100 K correspondingly. Single mode operation have been achieved in 70 divided by 140 micrometer long lasers with linewidth as narrow as 5 MHz, tuning rate as high as 210 cm^-1/A and subsidiary mode suppression up to 650:1. Methane detection at 3028.75 cm^-1 by wavelength modulation spectroscopy has been demonstrated.