基于ANSYS有限元分析法的LED结温检测

发光二极管(LED)作为第四代照明光源,其发光性能不但和电学特性相关,还受pn结结温的影响。LED的发光效率随着结温的升高而降低,LED的使用寿命也会随之减小。因此对LED结温进行准确检测具有重要的意义。利用Fluke Ti20红外测温摄像仪和ANSYS有限元软件模拟仿真结合的方法来分析LED模块的结温,并与标准电压法测得的结温进行对比。利用该方法获得的仿真结果与电压法实测LED结温值误差小于2%,与红外测温仪实测结果相差不超过5%。实验证实该方法可以作为LED非接触式结温分析的一种有效的工程方法。     

基于ANSYS有限元分析法的LED结温检测北大核心CSCD

发光二极管(LED)作为第四代照明光源,其发光性能不但和电学特性相关,还受pn结结温的影响。LED的发光效率随着结温的升高而降低,LED的使用寿命也会随之减小。因此对LED结温进行准确检测具有重要的意义。利用Fluke Ti20红外测温摄像仪和ANSYS有限元软件模拟仿真结合的方法来分析LED模块的结温,并与标准电压法测得的结温进行对比。利用该方法获得的仿真结果与电压法实测LED结温值误差小于2%,与红外测温仪实测结果相差不超过5%。实验证实该方法可以作为LED非接触式结温分析的一种有效的工程方法。     

瓦级大功率白光LED光色电特性研究

文章基于瓦级大功率白光LED在照明领域应用的广泛性和重要性,展开了瓦级大功率白光LED光色电特性的研究。采用大功率LED封装设备与紫外-可见光-近紫外光谱分析系统,制备并测量了瓦级大功率白色发光二极管（LED）在不同正向电流IF驱动下的光通量、电功率、发光效率、发射光谱和色品坐标等参数。研究表明,光通量与电功率随耳的增大呈亚线性增长的趋势,而荧光粉转换效率下降是影响其辐射功率的主要原因之一。当电流增大时,白光LED光谱的蓝光峰值出现先蓝移后红移的现象,而黄光部分光谱形状无明显变化。此外,色坐标x、y值均随着IF的增大而降低,主波长减小,色温值升高。     

“光荧光”光谱测试系统设计

光荧光（Photoluminescence,PL）是材料吸收光子后的一种自发放射。由于光荧光光谱对于检测半导体材料的光特性是一个有力而又无破坏的技术,根据放射特征光谱分析可获取材料的摻杂杂质种类、能隙大小、化合物中的组成成分、载流子寿命等重要讯息。文中从硬件和软件两个方面进行阐述,着重于光荧光光谱测试系统设计,完成测量光谱范围达到200-2000nm,测试精度达到1nA（1μV）,克服了传统测试系统灵敏度不高、测试光谱范围有限的缺点。     

ICP刻蚀p-GaN表面微结构GaN基蓝光LED

采用基于Cl2/Ar/BCl3气体的感应耦合等离子体(ICP)刻蚀技术制作了p-GaN表面具有直径3 μm、周期6 μm的二维圆孔微结构GaN基蓝光LED,研究了刻蚀深度对光荧光(PL)和发光二极管(LED)光电特性的影响.结果表明,刻蚀深度为25 nm的表面微结构,与传统平面结构相比,其PL增强了42.8%;而采用ITO作为透明电极的LED,在20 mA注入电流下,正面出光增强了38%、背面出光增强了10.6%,同时前向电压降低了0.6 V,反向漏电流基本不变.     

基于光致发光谱的窄禁带半导体材料能级研究

材料能带以及缺陷能级状态是窄禁带半导体材料芯片制造过程中的重要参数。红外调制光致发光（Photoluminescence, PL）光谱仪是一种无损的有效检测技术。利用该技术对不同的窄禁带半导体材料进行了检测,然后用线型拟合光谱揭示了不同能级间的电子跃迁,并对结果进行了分析。结果表明,红外调制PL光谱是一种有效的材料能带和缺陷能级研究方法。     

两款LED驱动器集成PFC支持TRIAC调光

具备可调光和PFC（功率因素校正）特性,能够精确控制并且具有高效、小体积和高可靠性,这些是目前LED照明驱动芯片需要面对的要求。针对这一需求,Power Integrations公司（PI）日前推出了两款支持TRIAC调光的单级PFC LED驱动器,其中,LinkSwitch—PH适合设计隔离式电源,LinkSwitch—PL适合设计非隔离式电源。     

电沉积工艺制备纳米ZnO及其生长机理

本文以Zn（NO3）2·6H2O和KCl的水溶液为电解液,采用三电极恒电位体系在ITO上电沉积制备了形貌可控的纳米ZnO。通过旋转涂布（CH3COO）2Zn·2H2O溶液,煅烧后可在ITO表面生长一层ZnO种子层。该种子层可以增加ZnO的密度,使c轴取向更加明显。通过场发射扫描电子显微镜（ FESEM）、X射线衍射（ XRD）、光致发光光谱（PL）等测试手段,系统地分析了电沉积参数（Zn（NO3）2·6H2O浓度、电沉积电压、电沉积温度）对电沉积制备纳米ZnO形貌、结构、光催化性能、发光性能的影响,并研究了其生长机理。     

半透明材料红外热像检测的光谱特性和光源选择

对半透明材料的光激励红外检测，其热激励机理与不透明材料不同，试件的吸热依赖于材料的光学特性和光源的辐射光谱。基于半透明材料的光谱特性，提出了体加热的物理机制和建模方法。为了获得材料的光谱吸收率，测试了不同厚度下玻璃纤维复合材料在一定波长范围内光的反射率和透射率。以色温模型来描述加热灯的光谱特性，用有限单元法分析了闪光灯色温对缺陷检测效果的影响，给出了可检信息参数（最大温差和最大对比度）与闪光灯色温的关系。结果表明，最大温差和最大对比度与色温呈非线性关系，它们随色温升高先减小后增大，因此低色温和高色温闪光灯对半透明复合材料检测更有利。所得结论为半透明复合材料的闪光灯激励红外检测提供了理论参考。     

LED受ESD冲击前后性能的变化分析

对GaN基蓝光LED施加ESD冲击,比较LED在受到ESD冲击前后I-V特性曲线、-5 V反向漏电流以及光色电特性的变化发现在I-V特性曲线和-5 V反向漏电流有明显变化的情况下,LED的光色电特性没有明显变化。选择在受到ESD冲击后反向漏电流值为不同数量级的LED作为样品进行加速老化实验,比较样品在加速老化实验前后的I-V特性曲线、光色电特性等参数的变化。通过比较样品之间的光衰减速率,发现反向漏电流大于1 mA时,样品的光衰减明显加快。     

Photoluminescence beyond 1.5 μm from InAs quantum dots

Photoluminescence measurements were carried out to investigate the origin of long wavelength emissions (1.6 μm at room temperature) observed from wafers with InAs quantum dots capped with GaAsSb layers. For wafers with high Sb content (22% and 26%) photoluminescence peak energies were found to be linearly proportional to third root of optical excitation power, a characteristic of emission due to a type-II band alignment. This work therefore presents unambiguous evidence that the long wavelength emission of the wafers comes from type-II band alignment between the InAs quantum dots and the GaAsSb capping layers.     

Liquid-crystal technique for observing integrated-circuit operation

A nondestructive technique has been developed that enables both the electric fields and temperature distributions at the surface of an operating integrated circuit to be viewed with conventional optical microscopes. Packaged chips or unscribed wafers are coated with a nematic liquid-crystal layer and operated in their normal fashion. Practical preparation and observation procedures have been developed.     

Separation of local bulk and surface recombination in crystalline silicon from luminescence reabsorption

Spontaneous photoemission of crystalline silicon provides information on excess charge carrier density and thereby on electronic properties such as charge carrier recombination lifetime and series resistance. This paper is dedicated to separating bulk recombination from surface recombination in silicon solar cells and wafers by exploiting reabsorption of spontaneously emitted photons. The approach is based on a comparison between luminescence images acquired with different optical short pass filters and a comprehensive mathematical model. An algorithm to separate both front and back surface recombination velocities and minority carrier diffusion length from photoluminescence (PL) images on silicon wafers is introduced. This algorithm can likewise be used to simultaneously determine back surface recombination velocity and minority carrier diffusion length in the base of a standard crystalline silicon solar cell from electroluminescence (EL) images. The proposed method is successfully tested experimentally. Copyright © 2009 John Wiley & Sons, Ltd.     

Calculation of quantitative shunt values using photoluminescence imaging

A proof of concept study for a method of determining quantitative shunt values in silicon solar cells from photoluminescence images is presented. The method is based on interpretation of the luminescence intensity around a local shunt or recombination‐active defect in terms of the extracted current. The theoretical relationship between the photoluminescence signal and the shunt current is derived. Experimental results on specifically prepared test structures show good agreement with known shunt resistance values. Experimental data on diffused wafers are presented. The effect of the front metallisation in complete cells on the appearance and interpretation of shunts in photoluminescence images is investigated experimentally. The limitations of the method are discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Selective bonding and encapsulation for wafer-level vacuum packaging of MEMS and related micro systems

A laser-assisted bonding technique is demonstrated for low temperature region selective processing. A continuous wave carbon dioxide (CO₂) laser (λ=10.6 μm) is used for solder (Pb37/Sn63) bonding of metallized silicon substrates (chips or wafers) for MEMS applications. Laser-assisted selective heating of silicon led to the reflow of an electroplated, or screen-printed, intermediate solder layer which produced silicon–solder–silicon joints. The bonding process was performed on fixtures in a vacuum chamber at an air pressure of 10⁻³ Torr to achieve fluxless soldering and vacuum encapsulation. The bonding temperature at the sealing ring was controlled to be close to the reflow temperature of the solder. Pull test results showed that the joint was sufficiently strong. Helium leak testing showed that the leak rate of the package met the requirements of MIL-STD-883E under optimized bonding conditions and bonded packages survived thermal shock testing. The testing, based on a design of experiments method, indicated that both laser incident power and scribe velocity significantly influenced bonding results. This novel method is especially suitable for encapsulation and vacuum packaging of chips or wafers containing MEMS and other micro devices with low temperature budgets, where managing stress distribution is important. Further, released and encapsulated devices on the sealed wafers can be diced without damaging the MEMS devices at wafer level.     

MOVPE生长1.3 μm无致冷AlGaInAs/InP应变补偿量子阱激光器研究

通过低压金属有机化学气相外延 (LP MOVPE)工艺生长了AlGaInAs应变补偿量子阱材料 ,通过X射线双晶衍射、光荧光、二次离子质谱的测试分析得到了材料生长的优化工艺参数 ,降低了材料中的氧杂质含量 ,得到了高质量AlGaInAs应变补偿量子阱材料 ,室温光致发光半宽FWHM =2 6meV。采用此外延材料成功制作了 1 3μm无致冷AlGaInAs应变量子阱激光器 ,器件测试结果为 :激射波长 :12 90nm≤ λ≤ 1330nm ;阈值电流 :Ith(2 5℃ )≤15mA ;Ith(85℃ )≤ 2 5mA ;量子效率变化 :Δηex(2 5～ 85℃ )≤ 1 0dB。     

Monolithic Perovskite/Silicon Tandems with >28% Efficiency: Role of Silicon-Surface Texture on Perovskite Properties

Textured silicon wafers used in silicon solar cell manufacturing offer superior light trapping, which is a critical enabler for high-performance photovoltaics. A similar optical benefit can be obtained in monolithic perovskite/silicon tandem solar cells, enhancing the current output of the silicon bottom cell. Yet, such complex silicon surfaces may affect the structural and optoelectronic properties of the overlying perovskite films. Here, through extensive characterization based on optical and microstructural spectroscopy, it is found that the main effect of such substrate morphology lies in an altering of the photoluminescence response of the perovskite, which is associated with thickness variations of the perovskite, rather than lattice strain or compositional changes. With this understanding, the design of high-performance perovskite/silicon tandems is rationalized, yielding certified power conversion efficiencies of >28%.     

Mapping of zinc content in Cd1−xZnxTe by optical methods

The paper compares different methods of optical mapping of zinc concentration x in Cd_1−xZn_xTe wafers for low x values and reviews the procedures for deriving band-gap energy from optical spectra (photoluminescence, absorption and reflectance) at different temperatures (liquid helium, liquid nitrogen and room temperature). Experimental errors of these techniques are compared and the segregation coefficient of zinc is calculated.     

Interface structural defects and photoluminescence properties of epitaxial GaN and AlGaN/GaN layers grown on sapphire

Overall characterization of the GaN and AlGaN/GaN epitaxial layers by X-ray diffractometry and optical spectral analysis is carried out. The layers are grown by metalloorganic gas-phase epitaxy on (0001)-oriented single crystal sapphire wafers. The components of strains and the density of dislocations are determined. The effects of strains and dislocations on the photoluminescence intensity and spectra are studied. The results allow better understanding of the nature and mechanisms of the formation of defects in the epitaxial AlGaN/GaN heterostructures.     

GaN基LED外延材料缺陷对其器件可靠性的影响

采用X光双晶衍射仪分析了GaN基发光二极管外延材料晶体结构质量并制成GaN-LED芯片,对分组抽取特定区域芯片封装成的GaN-LED器件进行可靠性试验.对比分析表明,外延晶片中的微缺陷与器件可靠性的关系密切;减少外延晶片中的微缺陷密度有利于提高LED器件的可靠性.通过建立从外延片晶体结构质量、芯片光电参数分布到器件可靠性的分析实验方法,为GaN-LED外延材料生长工艺的优化和改善提供依据,达到预测和提高器件可靠性的目的.