A strained-layer InGaAs-GaAs-AlGaAs single quantum well broadspectrum LED by selective-area metalorganic chemical vapor deposition

Three-step selective area metalorganic chemical vapor deposition is used to fabricate strained layer InGaAs-GaAs-AlGaAs single quantum well broad spectrum LEDs. We have fabricated a device with a continuous variation in quantum well thickness along its length by using a tapered oxide width mask for the active region regrowth. A spectral emission width of 80 nm is obtained     

Broadband emission from InGaAs-GaAs-AlGaAs LED with integratedabsorber by selective-area MOCVD

Three-step selective-area metal organic chemical vapour deposition is used to fabricate a strained layer InGaAs-GaAs-AlGaAs single quantum well broad spectrum LED with an integrated absorber. A tapered oxide width mask pattern is used for the active region regrowth to produce an edge emitting device with a continuous variation in the quantum well thickness and composition along its length. A maximum spectral width of 165 nm is obtained     

Narrow spectral width surface emitting LED for long wavelength multiplexing applications

We discuss a novel surface emitting InGaAsP LED with a relatively narrow spectrum obtained by the integral growth of a 2.6 μm thick semiconductor absorbing, or filtering, layer on a conventional double heterostructure device. The full width at half maximum for the filtered LED with peakpower atlambda_{0} = 1.29 mum isDeltalambda = 850Å (63 meV),compared with an unfiltered LED half width ofDeltalambda = 1300Å (97 meV). Half width measurements were made at a drive current density of 10 kA/cm². The optimization of the filtered LED is considered, and it is found that a substantial reduction of the power in the short wavelength spectral tail can be obtained without significantly decreasing the total LED output power. For these reasons, the filtered LED has potential applications for low cost wavelength division multiplexing systems where a low overlap of spectral output between adjacent wavelength channels is required. In addition, the narrow spectrum may prove useful in moderate bit rate (> 100 Mbits/s) multimode transmission systems where the output from broad spectrum, conventional surface emitting LED's leads to unacceptably high levels of signal dispersion.     

AlGaInP红、橙、黄光高亮度LED外延材料

采用金属有机化合物汽相淀积技术生长用于高亮度发光管 (UB-L ED)的 Al Ga In P/Ga As半导体微结构材料 ,突破了材料结构设计和材料生长工艺的关键技术 ,生长出满足于 Cd级的红、橙、黄光 L ED器件的外延材料。     

Broad-band emission from a multiple asymmetric quantum-well light-emitting diode

The authors demonstrate broadband light-emitting diode (LED) emission, with a full-width-at-half-maximum (FWHM) values >100 nm, based on concurrent multiple-state transitions in a single active layer containing two asymmetric quantum wells in the GaAs/AlGaAs material system. This spectral width is much broader (by a factor of 2.5) than that for commercial edge-emitting LEDs in the GaAs/AlGaAs system. The LED device is well suited for broadband source applications in wavelength-multiplexing-based, fibre-optic sensor network systems.<>     

Improved light extraction in AlGaInP-based LEDs using a self-assembly metal nanomask

This paper reports a new method of fabricating AIGaInP-based nanorod light emitting diodes (LEDs) by using self-assembly metal layer nanomasks and inductively coupled plasma.Light-power measurements indicate that the scattering of photons considerably enhances the probability of escaping from the nanorod LEDs.The light-intensity of the nanorod LED is increased by 34% for a thin GaP window layer,and by 17% for an 8μm GaP window layer.The light-power of the nanorod LED is increased by 25% and 13%,respectively.     

A New AlGaInP Multiple-Quantum-Well Light-Emitting Diode With a Thin Carbon-Doped GaP Contact Layer Structure

A new AlGaInP multiple quantum-well light-emitting diode (LED) with a thin carbon-doped GaP contact layer and a transparent conducting indium tin oxide film is fabricated and studied. For comparison, the LEDs with different contact layer structures are also included in this work. Experimental results indicate that the LED with a carbon-doped GaP contact layer exhibits a higher output power of 31.4 mW and a higher external quantum efficiency of 9%. The light–output power, under dc 20-mA operation, of this LED is increased by a factor of 18% as compared with that of conventional LEDs. These results are mainly attributed to the significantly lower series resistance and lower optical absorption effect. Moreover, the new device shows the reduced wavelength shift with 1.7-nm variation between 10 and 200 mA in electroluminescence spectrum.      

LED带抽运Nd∶YAG激光器

为了研究抽运光源光谱与增益介质吸收光谱对发光二极管(LED)带抽运激光器输出效率的影响,进一步提高输出效率,将光谱信息引入激光速率方程中,建立了LED带抽运速率方程, 采用该方法对LED带抽运Nd∶YAG激光器进行了理论分析和实验验证。结果表明,利用红外LED对Nd∶YAG激光器进行侧面抽运,当抽运能量为9.1mJ时,取得了能量为607μJ的1064nm激光输出,达到实验中最高的倾斜效率15.5%,此时光转换效率为6.67%;速率方程的计算求解和实验的输出能量二者基本吻合。这一结果对研究提高LED带抽运激光器的输出效率是有帮助的。     

Linear InGaAsP edge-emitting LED's for single-mode fibercommunications

A 1.3-μm edge-emitting diode with a linear radiance and high coupled power into a fiber is described. The LED yields 60 μW of coupled power into a single-mode fiber at a driving current of 100 mA and an ambient temperature of 25°C. A V-groove structure with an optical absorption region separated from an active region is used. At active layer thicknesses below 0.14 μm, linear current-light output characteristics are obtained. The spectral modulation depth is 0% over the entire emission spectral width of 75 nm, and coherence length is 22.5 μm. LED characteristics are achieved in the range from -30 to 85°C at a driving current of 100 mA. The LEDs exhibit a cutoff frequency of 250 MHz. LED reliability is discussed using results of accelerated aging carried out at the ambient temperatures of 50, 125, and 200°C. The activation energy of degradation is determined to be 0.63 eV, and LED half-lives are estimated to be in excess of 10⁶ h     

发光二极管的时间与空间相干性研究

由相干度理论和准单色光理论出发研究了发光二极管(LED)的时间相干与空间相干特性，并采用时间分辨为亚飞秒的迈克尔逊干涉仪对LED的相干度进行了测量记录。由记录所得的干涉图计算得到LED的发射光谱、相干时间及时间相干度；并通过比较其可见度和时间相干度推算出其空间相干度；最后提出由空间相干度计算LED发光面积的方法和使用LED光源测量材料中超快弛豫过程的可能性。分析了实验中的误差并提出修正方法，为采用LED作为稳态与时间分辨光谱光源提供了必要的理论与实验依据。     

白光LED的实现及荧光粉材料的选取

主要介绍了目前主流白光LED的封装方法,简述了各种方法的原理及优缺点。重点介绍了蓝光芯片与黄光荧光粉混合实现白光LED的机制。通过测试芯片发射谱、不同荧光粉材料的激发和发射谱,重点研究了蓝色芯片与黄色荧光粉材料的光谱匹配性,讨论了荧光粉材料的选取对器件的电学、光学性能的影响。     

Analysis of the illuminance provided by LED modules placed at large distances from illuminated objects

The possibility of applying LED modules for illumination of distant objects is analyzed. The illuminance distributions provided by large LED arrays with various optical systems are calculated. The influence of the number of LEDs, the intervals between LEDs, and the illumination angles on deviations from the law of inverse squared distance is studied. The conditions under which a variation in the LED elevation has only an insignificant effect on the illuminance and the radiation distribution over a limited illuminated area are determined.     

Cermet works on ZnO & GaN for Airforce,Navy and DoE

Cermet, which develops and manufactures semiconductor materials and devices based on gallium nitride (GaN), zinc oxide (ZnO), and related compounds has been selected by the Department of Energy to develop UV LEDs. In this it will develop nitride based UV LEDs on Cermet’s bulk aluminum nitride at specific emission wavelengths. The DoE is investing in UV LED technology to accelerate the implementation of solid state lighting.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.     

Correlated Color Temperature Tunable Multi-chip Light Emitting Diodes Light Source Design

One of the methods to derive white light from light emitting diodes（LEDs） is the multi-chip white LED technology, which mixes the light from red, green and blue LEDs. Introduced is an optimal algorithm for the spectrum design of the multi-chip white LEDs in this paper. It optimizes the selection of single color LEDs and drive current controlling, so that the multi-chip white LED achieves the target correlated color temperature （CCT）, as well as high luminous efficacy and good color rendering. A CCT tunable LED light source with four high-power LEDs is realized based on the above optimal design. Test results show that it maintains satisfactory color rendering and stable luminous efficacy across the whole CCT tuning range. Finally, discussed are the design improvement and the prospect of the future applications of the CCT tunable LED light source.     

Reliability investigation of light-emitting diodes via low frequency noise characteristics

Investigation of changes of operation and noise characteristics during aging process of light-emitting diodes (LEDs) has been carried out. Several groups of different design (different optics) LEDs based on different materials (nitride-based blue and white LEDs, phosphide-based red LEDs) have been investigated. It is found that leakage current components appear due to LED’s defects and their affect is observed as increase of both the low frequency electrical noise intensity and non-ideality factor of current-leakage characteristic in small current region. No considerable changes of light intensity characteristics during LEDs aging have been observed. Noise modeling, spectral and correlation analysis of optical and electrical fluctuations show on partly correlated optical and electrical fluctuations caused by defects in the active region of the LED. Degradation processes of investigated LEDs foremost occur in the diode chip and lead to the leakage current that has important affect to the electrical fluctuation level, but practically has a weak influence to the light emission properties of LED. Phosphorous layer of white LEDs and additional optical elements have no significant influence to the reliability of investigated LEDs under given aging conditions.     

Degradation analysis of secondary lens system and its effect on performance of LED-based luminaire

Degradation of a secondary lens system and its effect on LED-based luminaire performance are investigated. A polycarbonate plastic lens system is selected as a test vehicle. The lens system is aged under an actual user condition using high power warm white LEDs. The spectral power distributions (SPDs) of the LED/lens assembly are obtained before and after 9500 h of continuous operation. A detailed SPD analysis is followed to identify the most critical parameter of the lens system degradation.     

Analysis of LED modules for local illumination

Various variants of LED modules for local illumination are analyzed. The possibilities for approximation of LED luminous-intensity curves and for calculations of these curves in the TracePro system are considered. A method to calculate the illuminance of a 2D area via the 1D distribution of the illuminance along a line is proposed. A comparative analysis of the uniformity of the illumination and of the energy consumption is performed in the case when LEDs with different concentrations of luminous fluxes are employed. A possibility for rotation of LEDs via various optical systems for scattering and focusing of luminous fluxes is considered. In addition, the possibility of improving the uniformity of illumination through a decrease in the size of LED modules and a variation in the current of rotated LEDs is analyzed.     

Code Division-Based Sensing of Illumination Contributions in Solid-State Lighting Systems

Light-emitting diodes (LEDs) have emerged as a prime candidate for the light source of the future. To enable easy user interaction with a future lighting system consisting of many LEDs, this paper proposes a method to accurately measure and estimate the local light contributions of a large set of LEDs. This is enabled through tagging the light of each LED with an unique identifier. To this end, we propose a new family of modulation and multiple access schemes in this paper, named code-time division multiple access-pulse position modulation (CTDMA-PPM) and CTDMA-pulse width modulation (CTDMA-PWM). These schemes satisfy illumination constraints, are compatible with the commonly used PWM dimming of LEDs, and meet the multi-signal separation requirements for simultaneous measurement of illumination strengths. Based on these modulation methods, the paper develops algorithms to estimate illumination. Finally, performance analyses show that even for a very large number of LEDs, the sensing performance of the proposed system satisfies the requirements up to an adequate range.     

Tuning the performance of hybrid organic/inorganic quantum dot light-emitting devices

The luminescence of inorganic core-shell semiconductor nanocrystal quantum dots (QDs) can be tuned across much of the visible spectrum by changing the size of the QDs while preserving a spectral full width at half maximum (FWHM) as narrow as 30 nm and photoluminescence efficiency of 50% [Journal of Physical Chemistry B 101 (46) (1997) 9463] [1]. Organic capping groups, surrounding the QD lumophores, facilitate processing in organic solvents and their incorporation into organic thin film light-emitting device (LED) structures [Nature 370 (6488) (1994) 354] [2]. A recent study has shown that hybrid organic/inorganic QD-LEDs can indeed be fabricated with high brightness and small spectral FWHM, utilizing a phase segregation process which self-assembles CdSe(ZnS) core(shell) QDs onto an organic thin film surface [Nature 420 (6917) (2002) 800] [3]. We now demonstrate that the phase segregation process can be generally applied to the fabrication of QD-LEDs containing a wide range of CdSe particle sizes and ZnS overcoating thicknesses. By varying the QD core diameter from 32 Å to 58 Å, we show that peak electroluminescence is tuned from 540 nm to 635 nm. Increase in the QD shell thickness to 2.5 monolayers (∼0.5 nm) improves the LED external quantum efficiency, consistent with a Förster energy transfer mechanism of generating QD excited states. In this work we also identify the challenges in designing devices with very thin (∼5 nm thick) emissive layers [Chemical Physics Letters 178 (5–6) (1991) 488] [4], emphasizing the increased need for precise exciton confinement. In both QD-LEDs and archetypical all-organic LEDs with thin emissive layers, we show that there is an increase in the exciton recombination region width as the drive current density is increased. Overall, our study demonstrates that integration of QDs into organic LEDs has the potential to enhance the performance of thin film light emitters, and promises to be a rich field of scientific endeavor.     

Optically pumped “immersion-lens” infrared light emitting diodes based on narrow-gap III–V semiconductors

Spectral and power characteristics of light emitting diodes (LEDs) for the 3.3-to 7-µm range with GaAs LED pumping are presented. The LEDs consist of narrow-gap In(Ga)As, InAsSb(P), or InAs layers on a n ⁺-InAs substrate (band width ～λ_max/10) or on InSb (band width ～ 1 µm). The LEDs equipped with an immersion lens exhibit a conversion efficiency as high as 0.08–3 mW/A, which is comparable to or exceeds the highest reported data for the injection LEDs.