Subwavelength structures for broadband antireflection application

The subwavelength structures are designed and fabricated for broadband antireflection application. Under target of zero reflectivity, the parameters of periodic 2-D continuous conical structures are analyzed by the finite-difference time-domain (FDTD) method. The corresponding conical structures are obtained with spatial period of 350 nm and structure height of 300 nm, respectively. The 2-D continuous conical structured surface is fabricated by micro-replication process combining with the originated structure fabrication realized by interference lithography, Ni mold electroplation and replication by using UV imprinting into plastics. The average reflectances of the simulation and replicated polymer prototype are about 0.50% and 0.54% within the spectral ranges of 400-650 nm, respectively. In a word, the subwavelength structured surface with low reflection is developed and proved to be highly consistent with the simulation results.     

Solar cell fabrication using edge-defined film-fed growth (EFG) silicon wafers

The insufficient supply of polysilicon is limiting the growth of the segment of the photovoltaic industry using silicon materials. Because it is grown directly in the form of ribbon from a silicon melt, edge-defined film-fed growth (EFG) silicon ribbon is a promising alternative for cutting down wafer costs by reducing the polysilicon consumption and eliminating kerf loss. In this paper, we will discuss the various properties that can be achieved with for low cost and high-efficiency EFG silicon ribbon solar cell fabrication. Boron-doped p-type EFG ribbon silicon wafers with resistivities of 2-4 Ω cm and a size of 125 mm × 125 mm were used. The major fabrication steps we studied were mixed acid (HF, HNO₃, DI water) texturing, phosphorus diffusion with POCl₃, thermal oxide growth for surface passivation, laser process for edge isolation, and PECVD of SiN_x:H for surface passivation and antireflection coating. By optimizing the processing steps, we achieved a conversion efficiency, open circuit voltage, short circuit current, and fill factor as high as 14.5%, 584 mV, 32.1 mA/cm², and 77%, respectively.     

Antireflection subwavelength structures analyzed by using the finite difference time domain method

Antireflection subwavelength structures (ASSs) are analyzed by using the finite difference time domain (FDTD) method in the visible light spectrum. Low reflectance can be obtained by both the conical and pyramidal shapes over a broadband range. Comparing the reflectance of different structure shapes and aspect ratios by the FDTD method, it shows that the antireflection efficiencies of the pyramidal structures are better than that of the conical structures when the aspect ratio is up to 0.8. It is found that, for the conical structure surface, the average transmittance increases gradually with the aspect ratio and the average transmittance is about 99.6% with the aspect ratio of 2.0. However, for the pyramidal structure with the aspect ratio ranging from 1.0 to 2.0, the average transmittance is up to 99.7%.     

Subwavelength structured surfaces with a broadband antireflection function analyzed by using a finite difference time domain method

Subwavelength structured surfaces with a broadband antireflection function are analyzed by using a finite difference time domain method. The 2D periodic pure conical and pyramidal structures and several composite structured surfaces composing of conical and pyramidal structures are presented and discussed. It is found that the antireflection function will decrease for the same size of structures when the structure arrangement is discontinuous and the results of the structures with an aspect ratio of 2.0 are obviously better than the 1.0. It is also found that some composite structured surfaces have powerful antireflection function in the spectral ranges of 400-1400 nm within the 800-1200 nm spectral ranges.     

1.3μmInGaAsP/InP涂层结构超辐射发光二极管输出特性的理论和实验

本文用考虑了增益饱和和热效应的耦合速率方程,对减反射涂层结构1.3μmInGaAsP/InP超辐射发光二极管的输出特性进行了计算,给出了腔长、有源层厚度和后腔面反射率对其输出光功率的影响以及光谱半宽随腔长和注入电流的变化。计算结果与我们制备的该结构超辐射发光二极管测试结果有较好的符合。     

Influence of pre-surface treatment on the morphology of silicon nanowires fabricated by metal-assisted etching

Herein we demonstrate an improved metal-assisted etching method to achieve highly dense and uniform silicon nanowire arrays. A pre-surface treatment was applied on a silicon wafer before the process of metal-assisted etching in silver nitrate and hydrogen fluoride solution. The treatment made silver ion continuously reduce on silver nuclei adherence on the silicon surface, leading to formation of dense silver nanoparticles. Silver nanoparticles acting as local redox centers cause the formation of dense silicon nanowire arrays. In contrast, an H-terminated silicon surface made silver ion reduce uniformly on the silicon surface to form silver flakes. The silicon nanowires fabricated with a pre-surface treatment reveals higher density than those fabricated without a pre-surface treatment. The volume fraction improves from 18 to 38%. This improvement reduces the solar-weighted reflectance to as low as 3.3% for silicon nanowires with a length of only 0.87 μm. In comparison, the silicon nanowires fabricated without a pre-surface treatment have to be as long as 1.812 μm to achieve the same reflectance.     

Fabrication of broadband anti-reflective sub-micron structures using polystyrene sphere lithography on a Si substrate

Anti-reflective coatings are widely used on the surfaces of solar cells to increase the efficiency of photoelectric conversion. Sub-wavelength structures have gradually replaced conventional anti-reflective (AR) thin films due to their broadband AR properties. This paper successfully fabricated structures with a variety of surface morphologies on Si substrate using polystyrene sphere lithography in conjunction with two-step inductive coupling plasma (ICP) and high density plasma (HDP) etching processes. We successfully fabricated various sub-micron structures with heights of 700 nm and above. Experimental results show that the sub-micron pyramidal structure has the best anti-reflection performance with the average reflectance effectively suppressed to below 1% across the spectral range of 300–1200 nm.     

一维光子晶体中金属层内的电场分布增强

利用传输矩阵方法,研究了一维电介质-金属光子晶体的光学传输特性和金属层内的电场分布情况。计算结果表明,通过引入增透膜和优化结构参数,可以明显改变电介质-金属光子晶体的光学性能：在19%透射率的情况下,金属层内的平均电场相对于入射光场可以达到77%;而在金属层内平均电场相对入射光场为28%的情况下,可得到72%的透射率。这种可显著增强金属层内电场分布并且透射率、金属层内场强可调的光子晶体结构有望在非线性光子器件中得到重要应用。     

Anisotropic antireflection coatings: use as a laser intracavity polarization-direction selector

A double-layer anisotropic antireflection coating is designed and fabricated using the technique of serial bideposition. Both layers in the coating are biaxial with nanostructural columns directed normal to the substrate. Incident light with the p polarization encounters a pair of quarter-wave layers with refractive indices that satisfy the standard relationship for zero reflectance at the design wavelength. Light with the s polarization meets non-quarter-wave layers and different indices and hence is partially reflected. As an example to illustrate potential applications of the coating, we have used a thin glass plate with anisotropic antireflection coatings on both sides as an intracavity element to select the direction of polarization of an open-cavity HeNe laser.     

薄膜波导光栅滤光片反射特性研究

根据将减反射薄膜结构引入波导光栅滤光片中可以较好地抑制反射旁通带的理论,设计了单层、三层薄膜结构的波导光栅滤光片,旨在运用尽可能少的膜层数,在宽光谱范围内得到窄的反射带和高反射峰.运用严格的耦合波理论,对所设计的薄膜波导光栅滤光片的各种可能光栅结构进行了精确计算,得到反射率分布良好的特性曲线,并对计算结果进行分析,同时,还得到一种操作上较易于实现、在宽光谱范围内具有良好反射特性的三层膜光栅结构.