非平面化型ITO氮化镓基蓝光发光二极管

将氧化铟锡(ITO)生长于氮化镓基蓝色发光二极管的出光台面上(p型GaN台面),用非平面化处理的方法制作出ITO井状结构,研制出非平面化型氧化铟锡-氮化镓基蓝色发光二极管(LED),获得了高的出光效率.结果表明,在20mA工作电流下,该蓝色发光二极管的出光光强是平整的普通ITO-GaN基LED的1.35倍.     

阳极氧化铝工艺用于提高LED的出光效率

使用纳米尺度的多孔阳极氧化铝(anodic aluminum oxide,AAO)作为刻蚀掩膜,刻蚀氧化铟锡(indium-tin oxide,ITO),形成纳米图形化表面,对于发光二极管的出光效率有明显的提升作用。AAO纳米掩膜的制备已广为报道,是纳电子学研究中常用的模板之一,工艺简单易行、可控性好。使用电感耦合反应离子刻蚀方法成功将纳米多孔结构转移到ITO上,形成ITO纳米结构。纳米图形化结构的引入使得器件有效减小了内部的全反射,在电压没有大幅提高,注入电流350 mA时,光学输出提高了7%。纳米尺度粗化结构LED与传统结构LED对比,提升了器件的外量子效率。     

表面粗化提高GaN基LED光提取效率的模拟

影响GaN基LED的外量子效率低下的主要因素是光子在半导体和空气界面处的全反射.根据实际芯片建立LED模型,利用蒙特卡罗方法进行光线追迹模拟,分析了光子的主要损耗对出光效率的影响.计算不同的表面粗化微元,微元尺寸及微元底角对LED光提取效率的影响;比较不同微元形成的光场分布.模拟显示:所设计最佳的表面粗化结构在理想状况下可以提高光提取效率3倍以上.     

表面粗化提高倒装AlGaInP发光二极管的光提取效率

对发光二极管进行表面粗化能够大幅度的提高其光提取效率。利用晶片键合技术并采用湿法刻蚀的办法粗化n面AlGaInP表面制作了一种带表面粗化的倒装薄膜发光二极管。刻蚀后的表面形貌呈现金字塔状。270μm x 270μm管芯裸装在TO-18金属管座上,在20mA的注入电流下,粗化了的LED-I光强达到了315mcd,输出光功率达到了4.622mW,比没有粗化的LED-II的光功率高1.7倍。光功率增加的原因在于粗化后形成的这种金字塔状表面,其不但减少了背部镜面系统和半导体-空气接触面的反射,而且能有效的将光从LED中散射出去。     

高反射率电极及n-GaN表面粗化的InGaN/GaN多量子阱LED的研制

采用高反射率的Cr/Al/Pd/Au作为LED的p-GaN和n-GaN金属电极,替代低反射率的Cr/Pd/Au电极,减小了金属电极对光的吸收,使入射到高反射率金属电极的光经过反射后增加了出射概率,提高了光萃取效率.通过进一步粗化n-GaN表面,抑制了n-GaN/空气界面的光全反射,提高了光萃取效率.实验结果表明,在350 mA电流下,采用高反射率的Cr/Al/Pd/Au电极的LED相比传统电极LED光输出增加了14.3％;结合n-GaN表面粗化,LED的光输出则增加了35.3％.     

具有双光栅结构的高提取效率发光二极管的设计

设计了一种新型的具有较高光提取效率的双光栅结构的发光二极管,它在传统光栅发光二极管的有源层的下表面增加了光栅结构,提取出原本受限于全反射的光,获得了更高的光提取效率。利用三维严格耦合波理论对该结构的光学性能进行了分析,计算结果表明,这种新型的双光栅结构发光二极管的提取效率可达传统平板型的6.3倍。     

ITO掩膜干法粗化GaP提高红光LED的提取效率

采用氧化铟锡(ITO)颗粒掩膜,经感应耦合等离子体(ICP)刻蚀后制作了表面粗化的红光发光二极管(LED),并且研究了ITO腐蚀时间对粗化表面形貌的影响。测试结果表明,当粗化颗粒的大小为200～500 nm、腐蚀深度约200～400 nm时,能使制作的表面粗化红光LED在20 mA注入电流下光提取效率提高30%以上。并且,表面粗化不会影响LED的发光强度角度分布。     

掺半导体玻璃波导光栅耦合器及其功率限制作用

本文报导了在掺半导体玻璃波导上用离子刻蚀的方法制备出了表面刻蚀光栅耦合器。观察到了光栅耦合器的耦合效率随着输入激光功率增加而下降的功率限制作用。     

低损伤ICP刻蚀技术提高GaN LED出光效率

首先分析了在制作GaN基LED时,采用干法刻蚀技术会对材料的表面和量子阱有源区造成损伤,影响了GaN基LED的内量子效率。针对这个问题,研究实验采用感应耦合等离子反应刻蚀(ICP-RIE)技术,分别选择了氯气/三氯化硼(Cl2/BCl3)气体体系和氯气/氩气(Cl2/Ar)气体体系,通过优化射频功率、ICP功率、气体流量以及相应的真空度,得到了良好的刻蚀端面,对于材料造成的损伤较低,得到更好的I-V特性。实验结果表明,采用低损伤的偏压功率刻蚀后制作的LED器件,出光功率提升一倍以上,同时采用Cl2/Ar气体体系,改善了器件的I-V特性,有效提高了LED的出光效率。     

GaN基LED的图形衬底优化研究

设计了方形和阶梯状两大类的图形化蓝宝石衬底(PSS), 使用Crosslight公司的工艺软件CSuprem建立了三维的方形和阶梯状两类图形衬底GaN LED器件, 然后使用APSYS软件模拟计算出它们的光电特性。并且对方形图形衬底的刻蚀深度进行了优化, 通过对模拟结果的比较得到刻蚀深度与边长的比值为0.4时, 这种方形图形衬底GaN LED的光提取效率最高, 且比平面衬底提高了20.13%。对阶梯状图形衬底的阶梯层数进行了比较, 发现随着阶梯层数的增加, 光提取效率也随着增加, 阶梯状层数为5时, 光提取效率比平面衬底提高了30.03%。并对方形PSS LED进行了实验验证。     

Ni纳米粒子掩膜用于提高GaN基LED出光率的研究

以无水乙醇为溶剂、柠檬酸为分散剂,用超声分散技术配制Ni纳米粒子分散液;将分散液用旋涂的方法在GaN基发光二极管(LED)的ITO电流扩展层上制备单层Ni纳米粒子掩膜,采用ICP(inductively coupledplasma)干法刻蚀技术在ITO层上制作出表面粗化的结构。在20 mA工作电流下,与普通GaN基LED相比,这种ITO表面粗化的GaN基LED芯片发光强度提高了30%,并且对器件的电性能影响很小。结果表明,该表面粗化技术是一种工艺简单、成本低和能有效提高LED发光效率的方法。     

Optimization of the nanopore depth to improve the electroluminescence for GaN-based nanoporous green LEDs

GaN-based nanoporous green LEDs with different pore depth have been fabricated by using anodic aluminum oxide (AAO) as dry etching mask. The experimental results show that the electrical properties of the nanoporous LEDs with different pore depths are similar, but for the optical properties, the LEDs with nanopores extended to the p-GaN layer exhibits the best performance, if increase the depth to MQWs or decrease to the ITO layer will both decrease the light output power (LOP). By calculating the light extraction efficiency using three-dimensional (3D) finite-difference time-domain method, the decrease of the light output is mainly attributed to the reduced light extraction efficiency when the pore depth stop at ITO transparent layer instead of p-type layer, while if the depth reach the MQWs, the deterioration of the QWs which is caused by dry etching damage will play an important role. This optimization would give a valuable guidance to the surface structure design for nanostructured GaN-based LEDs, such as surface roughening, photonic crystal, or top-down fabricated surface-plasmon enhanced LEDs.     

聚苯乙烯球掩膜干法粗化提高LED发光效率

采用聚苯乙烯球作为掩膜层,对ITO(氧化铟锡)薄膜进行干法蚀刻实现ITO表面的粗化,提高GaN基大功率LED芯片外量子效率。利用AFM及SEM对ITO表面进行表征,比较了微球尺寸对ITO表面形貌及芯片光电参数的影响。结果表明,ITO表面经过350nm聚苯乙烯球图形化后,在未影响芯片正向电压和波长的前提下所制备的1mm×1mm波长为457nm的大功率LED芯片,亮度增加可达30%以上。     

多晶Si太阳电池表面酸腐蚀制绒的研究

研究了采用HF和HNO3非择优腐蚀多晶硅表面制备绒面的机理。通过实验分析了酸混合液的体积浓度配比、添加剂、温度和时间等因素对腐蚀速率和腐蚀后表面形貌的影响;总结出了多晶Si的酸腐蚀规律,得到了制备理想绒面的酸混合液体积配比(V(HF):V(HNO3):V(CH3COOH)=1∶12∶6)。在此基础上提出了优化设计方案:采用廉价的水代替醋酸作为缓蚀剂,腐蚀过程置于超声槽中进行,利用超声波的振动使反应生成的气泡快速脱离多晶Si片表面,同时使腐蚀液浓度分布更加均匀,从而制备出效果更佳的多晶Si绒面。     

Enhancement of Flip-Chip Light-Emitting Diodes With Omni-Directional Reflector and Textured Micropillar Arrays

The flip-chip light-emitting diodes (FC-LEDs) with a conductive omni-directional reflector and textured micropillar arrays were investigated. The micropillar arrays structure was formed on the bottom side of sapphire substrate by dry etching process to increase the light-extraction efficiency. The light output power of the FC-LED was increased by 65% for a 3.2-mum textured micropillar on the bottom side of the sapphire substrate. Our work offers promising potential for enhancing output powers of commercial light-emitting devices.     

Improved Light Extraction Efficiency in AlGaInP Light-Emitting Diodes by Applying a Periodic Texture on the Surface

In this letter, AlGaInP-GaP-based light-emitting diodes (LEDs) were fabricated with an Si substrate and an SiO₂-ITO-Ag omni-directional reflector using a metal-to-metal bonding technique. To enhance light extraction efficiency, a periodic texture was applied to the (Al_0.5Ga_0.5)_0.5In_0.5P surface layer of AlGaInP-Si LEDs by photolithography and a wet etching process. The exterior of the etched texture consists of a series of bowl-shaped recesses. With a 350-mA current injection, the typical output power of the AlGaInP-Si LEDs with and without the textured surface (LED-I and LED-II, respectively) were measured at approximately 118 and 81 mW, respectively, when the LED chips were bonded on the TO 46 without resin encapsulation. The enhancement of output power in LED-I can be attributed to a multitude of bowl-shaped notches on the surface, which resulted in a reduction of the reabsorption probability of the photons due to the fact that the photon path length in LED-I is shorter than in LED-II before the photons escape into the free space.     

Effect of NaOH solution on surface textured ZnO: Al films prepared by pulsed direct current magnetron sputtering

Transparent conducting Al-doped ZnO (ZnO:Al, AZO) thin films were prepared at substrate temperature of 270 °C by pulsed direct current magnetron sputtering. NaOH solution (5 wt%) was employed to etch the AZO films at room temperature, and the surface textured AZO films were obtained successfully. The relationship between the surface textured structures and the etching process controlled by etching time was discussed. The textured morphology of the etched AZO films became clear as increasing the etching time, and the AZO film etched for 30 min exhibited uniformly and distinctly crater-like surface textured structure. Correspondingly, the haze and the resistivity increased with the increasing etching time. And the resistivity of the AZO film etched for 30 min was 3.2×10⁻³ Ω cm.     

Wet etching mechanisms of ITO films in oxalic acid

This study examines how oxalic acid solutions affect indium tin oxide (ITO) etching. Experimental results show that the etching rate of ITO films increased linearly with the concentration of . The open circuit potentials included in the potential-pH diagrams for indium and tin in aqueous oxalic acid systems helped determine that ITO films was dissolved by the formation of in oxalic acid. However, the tin oxide in ITO films was difficult to dissolve, but could be removed by stripping. The EDS analysis and optical microscopic images indicate that the removal rate of SnO₂ in oxalic acid etchants was slower than that of In₂O₃, and many residues were distributed around the ITO bars after the etching process. Moreover, kinetic experiments reveal the high activation energy of ITO etching, and it was found stirring or ultrasonic vibration of the etchants had no influence on the dissolution rate of ITO films at all. Therefore, the rate-determining step should be the chemical reaction on ITO surface. A mechanism including protonation and ligand adsorption was proposed to explain the observed results.     

低温酸刻蚀对多晶硅表面织构化的影响

采用低温酸刻蚀,通过优化HF-HNO3-H2O腐蚀溶液体系配比及相关工艺参数,在多晶硅材料的表面制备了绒面结构,并进行SEM表面形貌分析和反射谱的测试。结果表明,低温刻蚀比常温刻蚀在生产工艺中更有利于控制反应速度,从而得到效果较好的绒面结构。研究中发现,在不同HF-HNO3-H2O腐蚀溶液体系配比中,温度对反应速率的影响有较大差异,当HNO3含量相对较低时,低温刻蚀工艺有较好的效果。所得最佳绒面制备方案为:酸腐蚀溶液体系配比为VHF∶VHNO3∶VH2O=1∶4∶2,温度为3℃,反应速率控制为2.6μm/min。该方案已在25MW多晶硅太阳电池生产线上实施,不增加工艺难度和生产成本,适合于工业生产。     

Texturization of mono-crystalline silicon solar cells in TMAH without the addition of surfactant

Texturization of mono-crystalline silicon solar cell by chemical anisotropic etching is still a key issue due to metal ions contamination and consumption of large amount of isopropyl alcohol (IPA) in a conventional mixture of potassium hydroxide (KOH) or sodium hydroxide (NaOH) and IPA. In this study, etching was performed on (100) silicon wafers using silicon-dissolved tetramethylammonium hydroxide (TMAH) solutions without addition of surfactant. Experiments were carried out in different TMAH concentration solutions at different temperatures for different etching time. The surface phenomena, etching rates, surface morphology and surface reflectance have been analyzed. Experimental results show that the resulted surface covered with uniform pyramids can be realized due to small changes of etching rates during the etching process. The etching mechanism has been explained basing on the experimental results and the theoretical considerations. It was suggested that all the components in the TMAH solutions play important roles in the etching process. Moreover, TMA+ ions may increase the wettability of the textured surface. A good textured surface can be obtained on conditions that the absorption of OH- /H2O is equilibrium with that of TMA+/SiO2(OH)22-.