GaN基蓝光发光二极管的波长稳定性研究

尽管GaN基蓝绿光发光二极管（LED）已进入大规模商品化阶段，但其发光波长随注入电流的变化仍是一个尚未解决的关键技术难题.同时，蓝绿光LED电注入发光光谱的半高全宽多为25nm以上.通过优化LED器件材料的生长条件和总应变量，获得了高质量的InGaN/GaN多量子阱LED外延片.由此制作的LED器件在0—120?mA的注入电流下，发光波长变化小于1nm.在20mA的正向电流下，其光谱半高全宽只有18nm，且随注入电流变化较小. 关键词： GaN 发光二极管 波长稳定性     

A study on polarization dependence of quadratic photocurrent in light emitting diodes using real time cross-polarized autocorrelation signals

An experimental study on the polarization dependence of the quadratic photocurrent in commercial light emitting diodes (LEDs) has been carried out using 200 fs laser pulses from a cw mode-locked Nd:glass oscillator. The variation of induced quadratic current with respect to orientation of polarization of the laser beam is measured using single and double beams. Cross-polarized autocorrelation measurements have been performed in real time at different orientations of the LEDs to differentiate the contributions to the quadratic photocurrent of two-photon absorption and second harmonic generation. The theoretical analysis of cross-polarized signals under different orientations is presented. PACS 42.65.Re; 42.65.ky; 42.50.Hz; 85.60.Jb     

Enhanced quadratic photocurrent in commercial light emitting diodes for autocorrelation measurement of ultrashort laser pulses

The quadratic photocurrent in commercial light emitting diodes (LEDs) has been studied in reverse bias mode for autocorrelation measurement of ultrashort laser pulses. It is found that the photocurrent can be greatly enhanced by operating the LED biased just below the reverse bias breakdown threshold. The effect of aging of LEDs on laser exposure in this mode of operation is found to be similar to that for the photovoltaic mode. The large internal gain in LED junction has enabled the recording of the second order autocorrelation signal of ∼200 fs laser pulses from 100 MHz laser oscillator with two orders of magnitude smaller average and peak power product compared to the case of the photovoltaic mode. PACS 42.65.Re; 42.50.Hz; 85.60.Jb     

GaN基双波长发光二极管电致发光谱特性研究

通过同时调节同一有源区内不同阱层和垒层的In组分，制备了GaN基单有源区蓝、绿光双波长发光二极管(LED).实现了20mA下蓝、绿光同时发射.实验发现随注入电流由10mA增大到60mA，电致发光(EL)谱中绿光峰强度相对于蓝光峰强度不断增强，峰值波长蓝移也更加明显.同时考虑极化效应和载流子不均匀分布的影响，通过对一维薛定谔方程、稳态速率方程和泊松方程的联立自洽求解.分析了测试电流下蓝、绿光EL谱峰值波长和功率的变化情况.发现理论结果与实验结果有很好地符合. 关键词： 极化 载流子不均匀分布 双波长     

Design and development of organic light emitting diodes

A highly luminescent thiophene based conjugated polymer, i.e., poly[2-(3-thienyl) ethanol butoxy carbonyl–methyl urethane] (PURET) has been used for fabricating polymeric light emitting diodes in the present investigations. PURET has been doped with varying amount of (4-dicyano methylene-2 methyl-6-(p-dimethyl amino styryl)-4H-pyran) dye. Enhanced electroluminescence (EL) and quantum efficiency has been observed by incorporating small amount of dye. An attempt has been made to understand the mechanism of charge transport, which helped in the understanding of the possible reasons for enhancement of EL emission as a function of dye concentration and allowed for further optimization of device performance. Based on capacitance–voltage (C–V) analysis it is proposed that the devices in the present investigations, may be modeled as a resistance and capacitor in parallel for the frequency range of 20 Hz–1 MHz. The enhancement in EL intensity and external quantum efficiency of PURET has been observed in addition of small amount of dye which is attributed to the trapping of excitons and enhanced probability electron–hole recombination in EL layer. In addition, voltage tunable color emission has also been observed. This is attributed to the charge transport among the various layers depending upon the applied voltage.     

发光二极管测试技术和标准

文章从发光二极管的空间能量分布和光谱能量分布两个方面叙述了光和辐射参数测试的原理和方法．讨论了辐射通量和光通量的基本概念、测量方法及相互之间的关系．在实际应用中，发光二极管的发光强度和辐射功率及他们的空间分布是常需要测量的参数．文章从基于人类视觉特性的色度学原理出发，讨论了发光二极管的光谱能量分布和重要的色度学参数以及相应的测试标准问题．     

发光二极管在差分吸收光谱系统中的应用研究

研究了新型发光二极管(LEDs)作为主动差分吸收光谱技术(DOAS)光源的可行性及其应用.分析了LEDs发光特性、谱的形状、光谱范围和谱的稳定性.结果表明LEDs作为主动DOAS光源是可行的,只是当温度不恒定时,LEDs光谱中的法布里-珀罗标准具效应将影响DOAS精确反演,若把其结构提取参与拟合可以很好地去除其影响.并成功地利用LEDs-DOAS系统监测了大气NO₂的浓度,与基于高压氙弧灯为光源DOAS系统测量结果的相关性达到0.99以上.当光程为0.7km时,检测限为1.1×10< 关键词： 发光二极管(LEDs) 差分吸收光谱技术(DOAS) 可行性     

金属有机化学气相沉积外延技术生长GaN基半导体发光二极管和激光二极管(Ⅱ)

如今，InGaN／GaN基量子阱发光二极管已经商业化，而且InGaN／GaN基量子阱激光二极管已实现连续波室温运转，使用寿命超过10000小时，虽然如此，但还没有完全搞清楚这些器件的发光机理．试验中通常使用连续输出He-Cd激光器（325nm）作光源，或者使用20—50mA注入电流来研究In—GaN量子阱样品或发光二极管光学性质，本文上篇研究了量子阱厚度与发光二极管发光功率的关系，lnGaN和GaN之间的晶格失配产生压电场，从而导致量子束缚斯塔克效应，而量子束缚斯塔克效应强     

On the stimulation of luminescence with green light emitting diodes

The present state of development of a green light emitting diode system, devised for convenient and economical optically stimulated luminescence dating, is described. The performance of the system is assessed in relation to use with feldspar and with quartz, both for material in which the latent signal was zeroed by heating and for material in which it was zeroed by bleaching. Aspects of assessment of the system include consideration of the measured signal-to-noise ratio and the consequently estimated minimum detectable dose, as well as the accuracy achieved in equivalent dose determination when simulating the dating process with laboratory dosed samples. A trial on quartz of equivalent dose determination by the single aliquot method is compared with use of the traditional multiple aliquot approach.     

Growth and properties of wide spectral white light emitting diodes

Wide spectral white light emitting diodes have been designed and grown on a sapphire substrate by using a metal-organic chemical vapor deposition system. Three quantum wells with blue-light-emitting, green-light-emitting and red-light-emitting structures were grown according to the design. The surface morphology of the film was observed by using atomic force microscopy. The films were characterized by their photoluminescence measurements. X-ray diffraction θ/2θ scan spectroscopy was carried out on the multi-quantum wells. The secondary fringes of the symmetric ω/2θ X-ray diffraction scan peaks indicate that the thicknesses and the alloy compositions of the individual quantum wells are repeatable throughout the active region. The room temperature photoluminescence spectra of the structures indicate that the white light emission of the multi-quantum wells is obtained. The light spectrum covers 400-700 nm, which is almost the whole visible light spectrum.     

Numerical and experimental studies of mixed-host organic light emitting diodes

Electrical characteristic and luminance of three mixed-host organic light emitting diodes (OLEDs): namely the uniformly mixed, step-wise graded and mixed, and continuously graded and mixed, were compared with the conventional hetero-junction OLED in both numerical and experimental studies. These mixed-host OLEDs were fabricated by a mixed-source thermal evaporation process, and half-cell devices were also fabricated to provide some input parameters for OLED simulations. The current efficiencies were largely influenced by their device structures and strongly agreed with the computed current balance factors. The improved mixed-host OLED performances can be discussed with aid from simulations, which include spatial distributions of electron and hole, carrier mobility, electric field profiles, the total recombination rates in the light emitting layer.     

氮化镓基发光二极管结构中粗化 p型氮化镓层的新型生长方法

提出了一种新型p型氮化镓粗化外延生长方法,这种生长方法的本质特征是利用低温生长的p型氮化镓作为粗化层的"晶籽"层,然后在这一层的基础上高温快速生长p型氮化镓,使粗化程度得到放大. 经实际制作尺寸为12 mil×10 mil的蓝光发光二极管器件并进行验证测试,与未进行p型氮化镓粗化的结果相比,通过这种方法粗化的发光二极管光通量可提升45%;结果同时表明,该方法有效解决了低温生长p型氮化镓带来的漏电流大,及预通镁源带来的前置电压高的问题. 关键词： 粗化 氮化镓 p型氮化镓 发光二极管     

Effects of parylene C layer on high power light emitting diodes

20 μm parylene C layer was deposited on silicone film to enhance the oxygen and water barrier properties, deposited at typical rate of 2.0 and 5.6 μm/h by controlling different deposited pressures. Surface morphology and roughness were observed by atomic force microscopy (AFM), surface morphology images show lower deposited rate that can lead to better quality film. 20 μm parylene C layer was deposited on silicone encapsulation of high power light emitting diodes (LEDs), the samples were tested by power temperature cycling (PTC) test from −40 to 85 °C, 15 min each extreme, and no corrosion, discoloration, cracks was found on the LEDs after the 1000 h PTC reliability test, and PTC test is intended to simulate worst case conditions encountered in typical applications, and parylene C floating membrane structure can stand such high stress and strain. Optical test on white and red LED samples with and without 20 μm parylene C layer, measurement result shows the optical transmittance more than 95%. 1000 h temperature humidity bias life test (T&HB) is performed for the purpose of evaluating the reliability of LEDs in humid environments, energy-dispersive X-ray (EDX) analysis revealed much lower content of C (carbon) and O (oxygen) on the lead frame of LED with parylene C coating after T&HB test on, and no oxidation was found in the LED package.     

金属有机化学气相沉积外延技术生长GaN基半导体发光二极管和激光二极管(Ⅰ)

文章评论性地介绍了金属有机化学气相外延技术（MOCVD）生长氮化物半导体GaN和InGaN以及激子局域化效应、量子束缚斯塔克效应对它们的光学性能的影响，详细比较了这两种效应对GaN基半导体发光二极管和激光二极管特性的影响，特别是量子束缚斯塔克效应以显著不同的方式影响着发光二极管和激光二极管的性能；文章还讨论了在A面蓝宝石衬底上生长GaN的情况．     

基于发光二极管和导光板的彩色光源色度的测量

介绍一种由三色发光二极管和导光板组成的适合物理实验色度测量教学的彩色面光源,并给出了测量该光源色度的实验方法．     

表面InGaN厚度对GaN基发光二极管特性的影响

通过调整GaN基发光二极管(LED)表面InGaN层的厚度,发现在20 mA电流驱动下,LED器件的正向压降有明显差距.本文考虑了极化效应的影响,通过求解InGaN/GaN三角形势阱内二维空穴气浓度以及空穴隧穿概率的变化,求得了表面InGaN层厚度不同时器件正向压降的变化趋势,发现理论结果与实验结果有很好的吻合.同时得到了获得最低正向压降的表面InGaN厚度. 关键词： 极化 二维空穴气 隧穿概率     

表面InGaN厚度对GaN基发光二极管特性的影响

通过调整GaN基发光二极管(LED)表面InGaN层的厚度，发现在20 mA电流驱动下，LED器件的正向压降有明显差距.本文考虑了极化效应的影响，通过求解InGaN/GaN三角形势阱内二维空穴气浓度以及空穴隧穿概率的变化，求得了表面InGaN层厚度不同时器件正向压降的变化趋势，发现理论结果与实验结果有很好的吻合.同时得到了获得最低正向压降的表面InGaN厚度.     

Effect of ZnO film thickness on the performance of organic light emitting diodes

The electrical and optical properties of the ZnO layers and of the ITO/ZnO bilayers are investigated. We show that a ZnO layer of about 120 nm is the best compromise to obtain simultaneously a high transmittance and conductivity. Moreover an X-ray diffraction analysis underscores that an amorphous ITO deposited on a polycrystalline ZnO could change into a polycrystalline ITO. The modifications of the ITO layer by a preliminary deposition of a 120 nm thick ZnO underlayer enables us to decrease the threshold voltage of organic light emitting diodes.     

Enhancement of the light extraction of GaN-based green light emitting diodes via nanohybrid structures

Improvement in the light extraction efficiency (LEE) of GaN-based green light emitting diodes (LEDs) with ZnO nanostructures synthesized by a hydrothermal method is reported. Formation of ZnO nanorods, hemispheres, and cones was controlled by varying the pH of the aqueous synthesis solution. The shape of the ZnO nanostructures integrated onto the LEDs shows a strong relationship with the LEE characteristics of GaN-based green LEDs. The electroluminescence (EL) intensity of LEDs covered by ZnO nanostructures increased compared to conventional LEDs. In terms of LEE, LEDs with surface-textured ZnO hemispheres showed the highest EL intensity, which can be attributed to an increase in the effective critical angle, the escape cone, and multiple scattering. Finite difference time domain (FDTD) simulation was conducted to theoretically confirm the experimental results.     

Influence of temperature on different optoelectronic characteristics of InGaN light emitting diodes

We have measured the electroluminescence (EL) and carrier lifetime characteristics in InGaN/Sapphire purple light emitting diode (LED), namely, UV3TZ-405-30 in a temperature range from 350 to 120 K and have compared them with those of a similar LED (UV3TZ-395-15) but with different Indium concentration, measured earlier. While it is found that for the present device the EL intensity decreases drastically with lowering of temperature after reaching a maximum (99%) at 228 K, this is markedly different from the previous device where intensity continues to increase monotonically till lowest temperature. This qualitatively distinct temperature dependence indicates difference in nature of localisation of carriers in the multiple quantum wells for varying Indium content in the two devices. The light–current–temperature data have been analysed in terms of the semiconductor rate equations to determine different optoelectronic properties. Next, estimating the ideality factor from the current–voltage (I–V) measurements, the effective carrier lifetime has been evaluated from the open circuit voltage decay process. Using the above measurements, the temperature dependence of the internal quantum efficiency of the device has been calculated and it is found to attain a maximum value of 99.88% at 228 K. Unlike all previous calculations, a unique feature of the present approach has been to include the effect of temperature dependence of the radiative recombination coefficient (B) in the rate equation analysis. Finally, a comparative study of the temperature dependence of the different optoelectronic properties of both devices is presented with and without this effect.