纳米压印多孔硅模板的研究

纳米压印模板通常采用极紫外光刻、聚焦离子束光刻和电子束光刻等传统光刻技术制备,成本较高.寻找一种简单、低成本的纳米压印模板制备方法以提升纳米压印光刻技术的应用成为研究的重点与难点.本文以多孔氧化铝为母模板,采用纳米压印光刻技术对纳米多孔硅模板的制备进行了研究.在硅基表面成功制备出纳米多孔阵列结构,孔间距为350—560 nm,孔径在170—480 nm,孔深为200 nm.在激发波长为514 nm时,拉曼光谱的测试结果表明,相对于单面抛光的硅片,纳米多孔结构的硅模板拉曼光强有了约12倍左右的提升,对提升硅基光电器件的应用具有重要的意义.最后,利用多孔硅模板作为纳米压印母模板,通过热压印技术,成功制备出了聚合物纳米柱软模板.     

晶体硅太阳电池表面纳米线阵列减反射特性研究

为增强晶体硅太阳电池的光利用率, 提高光电转换效率, 研究了硅纳米线阵列的光学散射性质. 运用严格耦合波理论对硅纳米线阵列在310—1127 nm波段的反射率进行了模拟计算, 用田口方法对硅纳米线阵列的表面传输效率进行了优化. 结果表明, 当硅纳米线阵列的周期为50 nm, 占空比为0.6, 高度约1000 nm时减反射效果最佳; 该结构在上述波段的平均反射率约为2%, 且在较大入射角度范围保持不变. 采用金属催化化学腐蚀法, 于室温、室压条件下在单晶硅表面制备周期为60 nm,占空比为0.53, 高度为500 nm的硅纳米线阵列结构, 其反射率的实验测试结果与计算模拟值相符, 在上述波段的平均反射率为4%—5%, 相对于单晶硅35%左右的反射率, 减反射效果明显. 这种减反射微结构能够在降低太阳电池成本的同时有效减小单晶硅表面的光反射损失, 提高光电转换效率.     

二维微纳米结构表面反射特性的时域有限差分法模拟研究

亚波长微纳米结构表面具有优良的抗反射特性,本文以硅基太阳能电池响应光谱的300~1 200 nm为应用基础,利用时域有限差分法计算了表面面形、结构参量的占空比、高度和周期以及光波入射角等对二维微纳米结构表面反射特性的影响,并结合等效介质理论进行了进一步理论分析,结果表明:等截面光栅结构的反射率较大,结构参量影响也较小;锥形渐变截面光栅结构的抗反射性能较好,且反射率随着占空比、结构高度的增大而显著下降;同时,光波在光栅法线的±40°范围内入射时,反射率均较小.通过对亚波长微纳米光栅结构的反射特性的模拟和分析,为抗反射表面的设计和制作提供了基础.     

银镜反应制备纳米蛾眼减反结构法

为了降低光学表面的菲涅耳反射,提出了一种制备仿生减反结构的方法.利用银镜反应并结合退火处理在硬性材质基底表面制备银纳米粒子,经反应离子刻蚀工艺,在基底表面形成一层纳米蛾眼减反结构.分析了周期分布和随机分布纳米蛾眼的光学特性,实验研究了退火参量和刻蚀参量对银纳米颗粒直径、密度以及高度的影响,并在硅和石英基底上分别制备了随机减反结构.测试结果表明:硅基平均反射率小于4.5%,双面石英基透过率达98.1%.理论和实验均表明:随机分布的纳米仿生蛾眼结构具有宽光谱、广视角和高减反特性,所提出的制备方法具有简便易行、低成本、大幅面等优点,在光电器件中具有良好的潜在应用前景.     

仿生纳米硅结构减反射及陷光性能模拟研究

仿造蝉翼凸起状结构,建立了硅纳米锥模型,在此基础上研究其减反射及陷光性能与其底部直径、高度的关系,确定直径150nm、高度500nm为其最优结构参数,该参数的纳米锥结构在300~1200nm波段平均反射率为1%.将优化的纳米锥结构与平板结构以及相同参数的纳米柱结构进行了比较,从反射曲线、电场强度分布、能量吸收密度分布、电子生成速度分布多个角度证实了纳米锥结构优异的减反射及陷光性能,为硅基光伏器件减反射陷光微结构设计提供了参考.     

仿生纳米硅结构减反射及陷光性能模拟研究EI北大核心CSCD

仿造蝉翼凸起状结构,建立了硅纳米锥模型,在此基础上研究其减反射及陷光性能与其底部直径、高度的关系,确定直径150nm、高度500nm为其最优结构参数,该参数的纳米锥结构在300~1200nm波段平均反射率为1%.将优化的纳米锥结构与平板结构以及相同参数的纳米柱结构进行了比较,从反射曲线、电场强度分布、能量吸收密度分布、电子生成速度分布多个角度证实了纳米锥结构优异的减反射及陷光性能,为硅基光伏器件减反射陷光微结构设计提供了参考.     

GaN基纳米阵列LED器件制备及发光特性

为了降低GaN材料中因应变诱导的量子斯托克斯效应,增加器件有源区内的电子-空穴波函数在实空间的交叠从而提高GaN基LEDs的发光效率,采用紫外软压印技术制备了均匀的周期性纳米柱阵列结构,结合常规LED器件微加工技术获得了In GaN/GaN基蓝光与绿光纳米阵列LED器件并对其进行了表征分析。结果表明:纳米柱阵列LED器件具有均匀的发光和稳定的光电性能。纳米结构不仅有效缓解了量子阱中的应力积累(弛豫度~70%),提高了器件的辐射复合几率和出光效率,同时结合纳米柱侧壁的化学钝化处理进一步降低了器件有源区的缺陷密度,显著降低了LED器件的漏电流(~10-7),最终提高了器件的发光效率。     

硅纳米线阵列光电探测器研究进展

硅(Si)作为最重要的半导体材料之一,被广泛应用于太阳电池、光电探测器等光电器件中.由于硅和空气之间的折射率差异,大量的入射光在硅基表面即被反射.为了抑制这种反射带来的损失,多种具有强陷光效应的硅纳米结构被研发出来.采用干法蚀刻方案多数存在成本高昂、制备复杂的问题,而湿法蚀刻方案所制备的硅纳米线阵列则存在间距等参数可控性较低、异质结有效面积较小等问题.聚苯乙烯微球掩膜法可结合干法及湿法蚀刻各自的优点,容易得到周期性硅纳米线(柱)阵列.本文首先概述了硅纳米线结构的性质和制备方法,总结了有效提升硅纳米线(柱)阵列光电探测器性能的策略,并分析了其中存在的问题.进而,讨论了基于硅纳米线(柱)阵列光电探测器的最新进展,重点关注其结构、光敏层的形貌以及提高光电探测器性能参数的方法.最后,简要介绍了其存在的主要问题及可能的解决方案.     

等离子体浸没离子注入制备黑硅抗反射层及其光学特性研究

表面织构是一种有效降低表面反射率、提高硅基太阳能电池效率的方法. 采用等离子体浸没离子注入的方法制备了黑硅抗反射层.分别通过原子力显微镜和紫外-可见-近红外分光光度计对黑硅样品表面形貌和反射率进行分析, 结果发现黑硅样品表面布满了高度为0—550 nm的山峰状结构, 结构层中硅体积分数和折射率随抗反射层厚度增加而连续降低. 在300—1000 nm波段范围内,黑硅样品的加权平均反射率低至6.0%. 通过传递矩阵方法对黑硅样品反射谱进行模拟,得到的反射谱与实测反射谱非常符合.     

基于BiFeO_3/ITO复合膜表面钝化的黑硅太阳电池性能研究

采用金属银辅助化学刻蚀法在制绒的硅片表面刻蚀纳米孔形成微纳米双层结构,以期获得高吸收率的太阳能电池用黑硅材料.鉴于微纳米结构会在晶硅表面引入大量的载流子复合中心,利用磁控溅射技术在黑硅太阳电池表面制备了BiFeO_3/ITO复合膜,并对其表面性能和优化效果进行了探索.实验制备的具有微纳米双层结构的黑硅纳米线长约180—320 nm,在300—1000 nm波长范围内入射光反射率均在5%以下.沉积BiFeO_3/ITO复合薄膜后的黑硅太阳能电池反射率略有提高,但仍然具有较强的光吸收性能;采用BiFeO_3/ITO复合膜的黑硅太阳能电池开路电压和短路电流密度分别由最初的0.61 V和28.42 mA/cm~2提升至0.68 V和34.57 mA/cm~2,相应电池的光电转化效率由13.3%上升至16.8%.电池综合性能的改善主要是因为沉积BiFeO_3/ITO复合膜提高了电池光生载流子的有效分离,从而增强了黑硅太阳电池短波区域的光谱响应,表明具有自发极化性能的BiFeO_3薄膜对黑硅太阳能电池的表面性能可起到较好的优化作用.     

基于二维矩形SiO2光子晶体光栅的研究

 为解决光学系统中普遍存在的菲涅耳反射问题,提高光的透射率,设计了一种二维矩形SiO2光子晶体结构光栅。采用勒让德多项式展开法对该结构在可见 近红外波长范围入射光波的透射率进行了模拟计算,寻找到了合适的占空比e、光栅深度h和基底厚度d,使得光栅的透射率在入射角为0～60°范围内、入射波长在400 nm～1 200 nm范围内变化时,其透射率的变化相对稳定,透射率的平均值可达到96%以上。     

Fresnel diffraction mirror for an atomic wave

We have experimentally demonstrated a material-independent mirror for atomic waves that uses the Fresnel diffraction at an array of parallel ridges. He* (2 (3)S(1)) and Ne* (1s(3)) atomic waves were reflected coherently on a silicon plate with a microfabricated grating structure, consisting of narrow wall-like ridges. We measured the reflectivity at grazing incidence as a function of the incident velocity and angle. Our data show that the reflectivity on this type of mirror depends only on the distance between the ridges, the wavelength, and the incident angle, but is insensitive to the material of the grating structure. The reflectivity is observed to increase by 2 orders of magnitude, compared to that of a flat polished silicon surface, where the reflection is caused by the attractive surface potential. For He* atoms, the measured reflectivity exceeds 10% for normal incident velocities below about 25 cm/s.     

Surface phenomena related to mirror degradation in extreme ultraviolet (EUV) lithography

One of the most promising methods for next generation device manufacturing is extreme ultraviolet (EUV) lithography, which uses 13.5 nm wavelength radiation generated from freestanding plasma-based sources. The short wavelength of the incident illumination allows for a considerable decrease in printed feature size, but also creates a range of technological challenges not present for traditional optical lithography. Contamination and oxidation form on multilayer reflecting optics surfaces that not only reduce system throughput because of the associated reduction in EUV reflectivity, but also introduce wavefront aberrations that compromise the ability to print uniform features. Capping layers of ruthenium, films ∼2 nm thick, are found to extend the lifetime of Mo/Si multilayer mirrors used in EUV lithography applications. However, reflectivities of even the Ru-coated mirrors degrade in time during exposure to EUV radiation. Ruthenium surfaces are chemically reactive and are very effective as heterogeneous catalysts. In the present paper we summarize the thermal and radiation-induced surface chemistry of bare Ru exposed to gases; the emphasis is on H₂O vapor, a dominant background gas in vacuum processing chambers. Our goal is to provide insights into the fundamental physical processes that affect the reflectivity of Ru-coated Mo/Si multilayer mirrors exposed to EUV radiation. Our ultimate goal is to identify and recommend practices or antidotes that may extend mirror lifetimes.     

Fabrication of large-scale periodic silicon nanopillar arrays for 2D nanomold using modified nanosphere lithography

We present a fabrication procedure that can form large-scale periodic silicon nanopillar arrays for 2D nanomold which determines the feature size of nanoimprint lithography, using modified nanosphere lithography. The size of silicon nanopillars can be easily controlled by an etching and oxidation process. The period and density of nanopillar arrays are determined by the initial diameter of polystyrene (PS) spheres. In our experiment, the smallest nanopillar has a full width half maximum (FWHM) of approximately 50 nm, and the density of silicon pillar is ∼10⁹/cm². Using this approach, it is possible to fabricate 2D nanoimprint lithography mask with 50 nm resolution.     

Fabrication of semiconductor-and polymer-based photonic crystals using nanoimprint lithography

The technology of fabricating photonic crystals with the use of nanoimprint lithography is described. One-and two-dimensional photonic crystals are produced by direct extrusion of polymethyl methacrylate by Si moulds obtained via interference lithography and reactive ion etching. The period of 2D photonic crystals, which present a square array of holes, ranges from 270 to 700 nm; the aperture diameter amounts to the half-period of the structure. The holes are round-shaped with even edges. One-dimensional GaAs-based photonic crystals are fabricated by reactive ion etching of GaAs to a depth of 1 μm through a mask formed using nanoimprint lithography. The resulting crystals have a period of 800 nm, a ridge width of 200 nm, and smooth nearly vertical side walls.     

多晶硅表面周期性微结构的激光制备与性能研究

为了减小多晶硅表面入射光的反射率,提高太阳能电池的光电效率,利用紫外纳秒激光器在多晶硅表面制备不同深度、不同间距的微凹坑点阵绒面,研究织构形貌对反射率及光电转换效率的影响.通过激光频率的改变实现微凹坑深度的变化,通过微凹坑排布方式的改变实现微凹坑间距的变化;使用光纤光谱仪测量多晶硅表面反射率并通过激光共聚焦显微镜观察微...     

Energetic Sn+ irradiation effects on ruthenium mirror specular reflectivity at 13.5-nm

Sn⁺ irradiations of Ru single-layer mirrors (SLM) simulate conditions of fast-Sn ion exposure in high-intensity 13.5 nm lithography lamps. Ultra-shallow implantation of Sn is measured down to 1–1.5 nm depth for energies between 1–1.3 keV at near-normal incident angles on Ru mirror surfaces. The Sn surface concentration reaches an equilibrium of 55–58% Sn/Ru for near-normal incidence and 36–38% for grazing incidence at approximately 63 degrees with respect to the mirror surface normal. The relative reflectivity at 13.5 nm at 15-degree incidence was measured in-situ during Sn⁺ irradiation. For near-normal Sn⁺ exposures the reflectivity is measured to decrease between 4–7% for a total Sn fluence of 10¹⁶ cm⁻². Theoretical Fresnel reflectivity modeling shows for the same fluence assuming all Sn atoms form a layer on the Ru mirror surface, that the reflectivity loss should be between 15–18% for this dose. Ex-situ absolute 13.5 nm reflectivity data corroborate these results, indicating that implanted energetic Sn atoms mixed with Ru reflect 13.5-nm light differently than theoretically predicted by Fresnel reflectivity models.     

Broadband antireflection gratings fabricated upon silicon substrates

We fabricated a two-dimensional subwavelength structured (SWS) surface upon a crystal silicon substrate. The SWS surface was patterned by electron beam lithography and etched by an SF(6) fast atom beam. The SWS grating had a conical profile, the period was 150 nm, and the groove was approximately 350 nm deep. The reflectivity was examined at 2002500-nm wavelengths. At 400 nm the reflectivity decreased to 0.5% from the 54.7% of the silicon substrate. We also used HeNe laser light to examine the reflectivity as a function of the incident angle.