High-efficiency resonant-cavity LEDs emitting at 650 nm

We fabricated resonant-cavity light-emitting diodes (LEDs) emitting at 650 nm. Compressively strained GaInP quantum wells were used as an active layer embedded between AlGaAs-AlAs Bragg mirrors. The Bragg mirrors formed a one-wavelength optical resonator. Two devices with different light-emitting areas were compared: 1) a large area chip (300 μm×300 μm) with a conventional LED contact and 2) a small area chip with an 80-μm light opening with an annular contact. Large devices are more suitable for high output power whereas the smaller devices might be useful for data transmission e.g., via plastic optical fibers. For epoxy-encapsulated large area devices, we achieved a maximum wall-plug efficiency of 10.2% and maximum output power of 12.2 mW at 100 mA. The small area LEDs yielded 2.9 mW at 20 mA and a maximum wall-plug efficiency of 9.5%     

Broadly-tunable resonant-cavity light-emitting diode

Microelectromechanical wavelength tuning is demonstrated for the first time in a resonant-cavity light-emitting diode. The device utilizes a deformable-membrane top mirror suspended by an air gap above a diode-active region and bottom mirror. Applied membrane-substrate bias produces an electrostatic force which reduces the air-gap thickness, and therefore, the resonant wavelength. We report broad tunability of nearly 40 nm and spectral linewidths as narrow as 1.9 nm (2.6 meV) for operation near 950 nm     

Modeling and performance of wafer-fused resonant-cavity enhancedphotodetectors

We discuss wavelength tuning and its corresponding quantum efficiency modulated by the standing wave effects in a resonant-cavity enhanced (RCE) photodetector. Specific design conditions are made for a thin In_0.53Ga_0.47As (900 Å) photodetector wafer-fused to a GaAs-AlAs quarter wavelength stacks (QWS). Analytic expressions for the calculation of resonant wavelength and standing wave effects are derived, using a hard mirror concept of fixed phase upon reflection, and are found to agree reasonably well with the exact numerical approach, using a transmission matrix method. We then experimentally demonstrate that wavelength tuning as large as 140 nm and its corresponding quantum efficiency modulated by the standing wave effects are clearly observed in our wafer-fused photodetectors, consistent with the predictions. The external quantum efficiency at 1.3 μm wavelength and absorption bandwidth for the wafer-fused RCE photodiodes integrated with an amorphous Si-SiO₂ dielectric mirror are measured to be 94% and 14 nm, respectively. This technique allows the formation of multichannel photodetectors with high quantum efficiency and small crosstalk, suitable for application to wavelength demultiplexing and high-speed, high-sensitivity optical communication systems     

High brightness visible (660 nm) resonant-cavity light-emittingdiode

Visible (660 nm) resonant-cavity light-emitting (RCLEDs) have been fabricated. The top-emitting devices employed two AlGaAs-AlAs-Bragg mirrors and GaInP-AlGaInP quantum-well active layers. The device performance was characterized as a function of the device diameters, ranging from 24 to 202 μm. The larger devices exhibited a nearly linear increase of output power with injected current with 8.4-mW emission at 120 mA. A maximum external efficiency of 4.8% was measured at 4 mA on the 84-μm aperture devices. All devices exhibited a narrow emission at 659-661 nm with a linewidth around 3 nm. The results show that RCLED's are promising low-cost light sources for plastic fiber transmission as well as display applications     

分光法测量LED颜色的不确定度分析

分析了分光法测试发光二极管(LED)颜色的测量不确定度,着重分析了光谱功率分布测量不确定度和波长不确定度对颜色测量的不确定度影响,给出了几种典型LED的分析结果,结果表明,5%的光谱功率分布测量不确定度和0.5 nm的波长不确定度在一般情况下可以满足精度要求为0.001的LED颜色测量.     

High-finesse resonant-cavity photodetectors with an adjustableresonance frequency

High speeds, high external quantum efficiencies, narrow spectral linewidths, and convenience in coupling make resonant-cavity photodetectors (RECAP's) good candidates for telecommunication applications. In this paper, we present analytical expressions for the design of RECAP's with narrow spectral linewidths and high quantum efficiencies. We also present experimental results on a RECAP having an operating wavelength λ₀≈1.3 μm with a very narrow spectral response. The absorption takes place in a thin In_0.53Ga_0.47As layer placed in an InP cavity. The InP p-i-n structure was wafer bonded to a high-reflectivity GaAs/AlAs quarter-wavelength Bragg reflector. The top mirror consisted of three pairs of a ZnSe/CaF₂ quarter-wavelength stack (QWS). A spectral linewidth of 1.8 nm was obtained with an external quantum efficiency of 48%. We also demonstrate that the spectral response can be tailored by etching the top layer of the microcavity. The results are found to agree well with those obtained from analytical expressions derived on the assumption of linear-phase Bragg reflectors as well as detailed simulations performed using the transfer matrix method     

一种非接触大功率白光LED结温测量方法

本文以不同色温类型的1W大功率白光LED为研究对象,通过改变工作电流和环境温度,对LED的结温和光谱之间的关系进行了研究。研究结果表明,无论对冷白光LED还是对暖白光LED,无论是电流还是环境温度引起的结温的变化,LED管光谱中白光光谱积分与蓝光光谱积分比值(R=W/B)都随结温呈现线性变化。因此,可以利用LED的辐射光谱进行结温的非接触快速测量是可行的,其最大的优点是不需要破坏器件的封装或LED灯具的整体性,是一种理想的结温测量方法。     

Ensuring accuracy in optical and electrical measurement of ultra-bright LEDs during reliability test

In order to accurately estimate the lifetime of Light Emitting Diodes (LEDs), accelerated stress tests have to be performed, and measurements done throughout the tests should be free of artifact and repeatable to ensure accurate observations of the degradation of the LEDs. In this work, measurements artifact arising from DC biasing and PWM settings were first presented. Electrical measurements consistency was then studied. Optimized setting for accurate measurement is obtained using Response Surface Method with Central Composite Design, and the setting is verified through experiments.     

Design and fabrication of temperature-insensitive InGaP-InGaAlP resonant-cavity light-emitting diodes

Visible InGaP-InGaAlP resonant-cavity light-emitting diodes with low-temperature sensitivity output characteristics were demonstrated. By means of widening the resonant cavity to a thickness of three wavelength (3/spl lambda/), the degree of power variation between 25 /spl deg/C and 95 /spl deg/C for the devices biased at 20 mA was apparently reduced from -2.1 dB for the standard structure design (1-/spl lambda/ cavity) to -0.6 dB. An output power of 2.4 mW was achieved at 70 mA. The external quantum efficiency achieved a maximum of 3% at 13 mA and dropped slowly with increased current for the device. The external quantum efficiency at 20mA dropped only 14% with elevated temperature from 25 /spl deg/C to 95/spl deg/C. The current dependent far-field patterns also showed that the emission always took place perfectly in the normal direction, which was suitable for plastic fiber data transmission.     

Analysis of a resonant-cavity enhanced GaAs/AlGaAs MSMphotodetector

The authors have developed a 2-D device simulator for heterostructure metal-semiconductor-metal (MSM) photodetectors. They have incorporated a model of multilayer optics into the simulator and used it to analyze the temporal response of a resonant-cavity enhanced heterostructure with a confining buffer layer and a distributed Bragg reflector (DBR). The authors show that through fine tuning the layer thicknesses, optical resonance enhancement of the light absorption can be obtained     

Transmission analysis on the resonant-cavity combiner of mobileradio transmitters

A general approach to the transmission loss analysis of resonant-cavity combiners of the type used in cellular and in other mobile radio systems is described. A simple closed-form solution is derived for a particular type of combiner in which the cavities are connected in a star configuration via transmission lines that are odd multiples of quarter-wavelength long at the center frequency. This is an exact solution at the center of the combiner band in which one cavity is tuned to this frequency and other cavities are tuned symmetrically in pairs about this frequency. For narrow-band combiners, such as those used in cellular systems, the transmission loss obtained from this solution should be accurate for the entire band. The analysis is valid over wide ranges of combiner parameters: loaded and unloaded Q's of cavities, frequency spacings, and the number of ways it is combined. The comparison of the analytic results with laboratory measurements, although limited in scope, shows that they are in good agreement     

Phase-shift technique for the measurement of chromatic dispersion in single-mode optical fibres using LEDs

The phase-shift technique has been successfully extended to chromatic dispersion measurements in single-mode optical fibres. Using only two sinusoidally modulated LEDs operating at 1.33 and 1.47 ?m, accurate results have been achieved in the spectral region of interest, in good agreement with those obtained with the Nd-Yag laser and Raman fibre technique.     

Blue perovskite LEDs

Metal halide perovskite light-emitting diodes (PeLEDs)show great potential in ultra-high-definition displays,due to their narrowband emission,wide color gamut (～140％),and cost-effective solution processability[1]M.Thanks to scientists' tremendous efforts,the external quantum efficiencies (EQEs)for the state-of-the-art PeLEDs emitting near-infrared and green light have reached 21.6％[2] and 23.4％[3],respectively.However,blue PeLEDs,as one of the essential technologies for perovskite-based high-resolution monitors and white light-ing,are still inferior to their red and green counterparts.Blue emission is usually achieved by using dimensional engineer-ing (quantum confinement) or composition engineering(mixed halides,e.g.,mixed Br/Cl) strategies.For example,quasi-two-dimensional (2D) perovskites,nanocrystals (e.g.,quantum dots,QDs) or nanoplates,give blue emission due to quantum confinement effects.However,achieving pure-blue(465-475 nm) and deep-blue (420-465 nm) light from quasi-2D perovskites is challenging[4],while ultra-small QDs and nanoplates suffer from high surface trap density and poor sta-bility[5].For PeLEDs based on mixed Br/Cl perovskites,the emis-sion peak can be tuned easily,but these perovskites face the disadvantages of phase separation and deep energy-level Cl vacancies[4].     

OLED的电源管理

为OLED选择电源管理IC是一个严峻的挑战 在今后的几年内,有机发光二极管（OLED）无疑将突破手机副屏这一目前的主要应用领域。韩国市场调研公司Display Bank的研究表明,由于更多的数码相机、MP3播放器和掌上游戏机等便携产品的生产商开始采用OLED,其全球销售量今年将增长64％（从2005年的6100万件到2006年的约1亿件）。     

Metal-mirror-based resonant-cavity enhanced light-emitting diodesby the use of a tunnel diode contact

We, for the first time, designed and fabricated resonant-cavity light-emitting diodes for high-speed optical communications using a tunnel diode contact scheme. Use of a tunnel diode provides extra freedom in designing the device contact and cavity mirror, which allows the realization of a resonant cavity without requiring distributed Bragg reflectors. The fabricated resonant-cavity light-emitting diodes have half the spectrum bandwidth and nearly triple the fiber-coupled power of noncavity devices     

ZnSe-based mixed-color LEDs

II-VI mixed-color light-emitting diodes (LEDs) were prepared by molecular beam epitaxy. At 20 K, it was found that we could achieve a near white light emission from sample 1O2B quantum well with a Commission Internationale de Enluminure index of x=0.4 and y=0.45. By carefully designing the device structure, we should be able to achieve a phosphor free white light LED by using the combinations of ZnCdSe and ZnCdSeTe wells.