具有光学结构的超导纳米线吸收效率的仿真

超导纳米线单光子探测器(SNSPD)的系统探测效率由纳米线与光子的耦合效率、纳米线的吸收效率以及纳米线吸收光子后能产生电压脉冲的本征量子效率决定。设计了一种带有防反射层、谐振腔、布拉格反射镜等结构的SNSPD。利用COMSOL软件的射频模块对这种新型结构的SNSPD进行了仿真,结果表明具有光学结构的SNSPD将有助于提高系统探测效率。     

强吸收结构高速超导纳米线单光子探测器

本文研究具有强吸收结构的高速超导纳米线单光子探测器(SNSPD)的设计与仿真.该SNSPD基于高折射率入射介质和空气腔结构,可以提高超导纳米线的光子吸收率.与现有超导单光子探测器结构相比,在相同材料和厚度的超导超薄膜制成纳米线的条件下,用更低的占空比就可以实现接近于100%的吸收率,这使得电子束曝光步骤的难度大大降低.而SOI衬底的采用则可以同时保证超导薄膜的高质量生长,不影响探测器的本征量子效率.另外,在保证同样大的有效探测面积的条件下,由于需要的纳米线的总长度显著减小,制备过程中发生缺陷的概率显著降低,探测器的最高计数率可以得到提升.     

太赫兹波段介质微腔光学特性研究

采用匀胶法制备了厚度在微米量级的 Si/[TiO₂/Al₂O₃]²TiO₂和Si/[TiO₂/MgO]²/TiO₂ 多层介质膜反射镜. 采用太赫兹(THz)时域透射光谱系统获得了多层膜的时域透射谱. 用传输矩阵法模拟了Si/[TiO₂/Al₂O₃]²TiO₂ 和Si/[TiO₂/MgO]²/TiO₂两种分布式布拉格反射镜 (DBR)的反射相移和相位穿透深度等光学特性. 设计了两种结构为 DBR/LT-GaAs/DBR的对称THz光学微腔结构并模拟了腔结构的辐射光谱. 结果表明:通过引入谐振腔, 两种DBR组成的微腔器件在谐振波长处的强度分别提高了19和14倍. 其中Si/[TiO₂/Al₂O₃]²TiO₂/LT-GaAs (12 μm)/ [TiO₂/Al₂O₃]²TiO₂腔的辐射光谱存在两个峰, 分别位于208和248 μm, 并分析了出现两个谐振峰的原因. 探讨了通过引入介质谐振腔实现对THz源的辐射特性进行调控的可行性. 关键词： 分布式布拉格反射镜 光子晶体 穿透深度 太赫兹微腔     

超导纳米线多光子响应特性研究

研究了超导单光子探测器器件超导纳米线的多光子响应特性.在温度3.5 K实验测量了纳米线器件直流特性和比子响应概率对多光子脉冲信号的响应特性.实验表明,器件超导转变电流随光辐照强度的增加而减小;在多光子脉冲信号下,器件响应的光子数随偏置电流减小而增加.同时基于量子光学和器件Hotspot理论半定量分析了该多光子响应的机制.     

铌钛中空超导电缆接头的直流特性分析

超导电缆接头是超导磁体的关键部件之一,其性能直接影响超导磁体的运行稳定性。通过对超导电缆接头的直流特性分析,可以比较全面详实的了解接头中电流的分布规律,并据此设计超导接头的最佳连接方式和尺寸。分析采用的软件是OPERA 13.0,建立并计算了超导接头全尺寸简化模型、1/33分段股线模型和1/33分段单侧股线模型,3类共计48个模型。在以减少超导接头引起的电缆载流能力损失,即做到各股线电阻的尽可能一致,并将接头整体电阻控制在nΩ级为目标,通过48个模型的计算结果,确定了中空超导电缆接头的最佳几何参数,分析了影响接头电流分布的关键因素。     

GaAs纳米线晶体结构及光学特性

采用分子束外延技术在N-型Si (111)衬底上利用自催化生长机制外延砷化镓(GaAs)纳米线,对生长的纳米线进行扫描电子显微镜测试,纳米线垂直度高,长度直径均匀度好.对纳米线进行光致发光(photoluminescence, PL)光谱测试,发现低温10 K下两个发光峰P1和P2分别位于1.493 eV和1.516 eV,推断可能是纤锌矿/闪锌矿(WZ/ZB)混相结构引起的发光以及激子复合引起的发光;随着温度升高,发现两峰出现红移,并通过Varshni公式拟合得到变温变化曲线.对纳米线进行变功率PL光谱测试,发现P1位置的峰位随功率增加而蓝移,而P2位置的峰位不变.通过拟合发现P1峰位与功率1/3次方成线性相关,判断可能是WZ/ZB混相结构引起的Ⅱ型发光;同时,对P2位置的峰位进行拟合,P2为激子复合发光.对纳米线进行拉曼光谱测试,从光谱图中发现GaAs WZ结构特有的E_2声子峰,因此证明生长出的纳米线为WZ/ZB混相结构,并通过高分辨透射电子显微镜更直观地观察到纳米线的混相结构.     

硅纳米线阵列的光学特性

在常温常压条件下,采用改进的金属催化化学腐蚀方法在n型单晶硅片(100)上制备了大面积垂直于硅衬底、直径均匀、排列整齐的硅纳米线阵列。分析了样品的表面形貌和反射谱,纳米线直径为10~50 nm。在腐蚀时间分别为15,30,60 m in时,纳米线长度分别为9,17,34μm。样品的减反射性能优异,在300~1 000nm波段,得到了2.4%的反射率。初步分析了纳米线阵列的减反射机制和不同腐蚀时间样品的反射率差异。     

基于共振腔发光二极管的DBR温度特性研究

分布式布拉格反射镜（DBR）是共振腔发光二极管（RCLED）的主要组成部分,其温度特性对RCLED的性能有着重要影响。基于650 nm红光RCLED,设计出由Al0.5Ga0.5As和Al0.95Ga0.05As组成的DBR结构。首先通过AlxGa1-xAs材料折射率的色散关系分析温度对AlxGa1-xAs材料折射率的影响,进而模拟了DBR反射谱的温度特性,得到随着温度升高DBR反射谱红移的结论,温漂速率为0.048982 nm/℃。通过MOCVD制备出30对Al0.5Ga0.5As和Al0.95Ga0.05As组成的DBR外延结构,并对其进行反射谱测试,发现随着温度升高反射谱出现了红移现象,温漂速率为0.049277 nm/℃,与模拟结果相近,验证了温度升高导致反射谱红移结论的正确性。     

体全息光学元件布拉格偏移特性的研究及其应用

本文研究了体全息光学元件的布拉格(Bragg)偏移及补偿特性,得出了在某些调制度下,在偏移布拉格条件下仍可以得到较高的衍射效率的结论.文中也讨论了体全息光学元件布拉格偏移的容忍性并分别讨论了体全息元件布拉格偏移所允许的角度偏移和再现波波长偏移的性质,得出了在大调制度下体全息光学元件的布拉格偏移容忍性大的结论.同时指出实现体全息光学元件高衍射效率的变波长再现的途径,并给出相应的实验结果.     

Optical properties of indium nitride powder and films

Using photoluminescence and transmission measurements, we have studied the optical properties of indium nitride powder and thin films grown by molecular beam epitaxy. The bandgap for InN powder with electron concentration ∼ 4·10¹⁹ cm⁻³ was 0.94 eV, and for InN films with electron concentrations ∼10¹⁸ cm⁻³ it was 0.7 eV. We have established that when the electron concentration is increased to 8·10¹⁹ cm⁻³, the bandgap of InN increases to 1.0 eV. The change in the bandgap as a function of the concentration is due to the appearance of the Burstein-Moss effect. Report given at the Fifth Belorussian-Russian Seminar on Semiconductor Lasers and Systems Based on Semiconductor Lasers, June 1–5, 2005, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 86–89, January–February, 2006.     

Optical and physicochemical properties of hydrogenated silicon nitride thin films: Effect of the thermal annealing

The effect of thermal annealing on the optical and physicochemical properties of hydrogenated silicon nitride films was studied. These films were deposited by plasma-enhanced chemical vapor deposition from a mixture of silane, ammonia, and nitrogen. Subsequently, the films were annealed at various temperatures ranging from 400°C to 1000°C. The properties of the films were studied using ellipsometry and Fourier transform infrared spectroscopy. The Maxwell Garnet model considers the silicon nitride material as heterogeneous with three distinct phases: silicon, stoichiometric silicon nitride, and hydrogen. Based on the ellipsometric analysis, the annealing treatment leads to reduce the volume fraction of both hydrogen and silicon. As a result, the stoichiometry parameter significantly increases from 1.24 to 1.32 making it closer to the stoichiometric silicon nitride one. According to the infrared data, a noticeable decrease in the total hydrogen concentration in the films was obtained with respect to the annealing temperature.     

Optical harmonic generation in amorphous silicon nitride microcavities

Second harmonic (SH) and third harmonic (TH) generation in amorphous silicon nitride microcavity are experimentally investigated. The transmitted SH and TH signals are measured in the 0.9-1.4 μm spectral range, showing enhanced nonlinear conversion efficiency corresponding to resonant wavelength and optical band edges. The efficiencies of the SH and TH generation processes are found to be enhanced by about two and one orders of magnitude, respectively, in comparison with the case of reference amorphous silicon nitride sample. The SH spectra can be reasonably interpreted as due to surface/interface harmonic generation, while the TH signal is related to bulk isotropic third-order polarization. The results obtained for the TH signal are discussed in terms of the linear optical properties of amorphous silicon nitride thin films.     

Photoluminescence and optical absorption properties of silicon quantum dots embedded in Si-rich silicon nitride matrices

Silicon nitride (SiN_x) films were prepared with a gas mixture of SiH₄ and NH₃ on Si wafers using the plasma-enhanced chemical vapor deposition (PECVD) method. High-resolution transmission electron microscopy and infrared absorption have been used to reveal the existence of the Si quantum dots (Si QDs) and to determine the chemical composition of the silicon nitride layers. The optical properties of these structures were studied by photoluminescence (PL) spectroscopy and indicate that emission mechanisms are dominated by confined excitons within Si QDs. The peak position of PL could be controlled in the wavelength range from 1.5 to 2.2 eV by adjusting the flow rates of ammonia and silane gases. Absorbance spectra obtained in the transmission mode reveal optical absorption from Si QDs, which is in good correlation with PL properties. These results have implications for future nanomaterial deposition controlling and device applications.     

Optical properties of metallic nanowires

The optical response of metallic nanowires is determined taking into account the non-local electron response by use of a self-consistent method and a jellium model. An exact formula for the reflection factor is obtained in the usual case of an hydrodynamic dielectric function. Up to a constant factor it coincides with the non-retarded limit of the amplitude obtained in a previous calculation, leading finally to the same extinction function. This function is calculated for certain metallic nanowires of experimental interest (Na, Ag). From the non-retarded near field response, the scattering amplitude at any distance can be derived.     

聚合物前驱体制备氮化硅纳米纤维及其发光

由聚硼硅氮烷前驱体在高温常压下热裂解得到氮化硅纳米纤维,确定了样品结构为α相,讨论了纳米纤维的生长模式属于气-液-固生长机制。在室温下用488nm激光对样品激发,观察到样品有很宽的强光致发光带,并有两个发光中心,这种强的可见光致发光主要来自氮化硅的内禀Si和N的悬键。测量了纳米纤维的室温吸收光谱,得到氮化硅纳米纤维的光学带隙为4．80eV。     

基于纳米硅结构的氮化硅基发光器件电致发光特性研究

利用等离子体增强化学气相沉积法制备了镶嵌于氮化硅的高密度纳米硅薄膜,并以此作为发光有源层构建基于p-Si/氮化硅基发光层/AZO结构发光二极管,在室温下观察到了电致可见发光.在此基础上,在器件p-Si空穴注入层与氮化硅基发光层之间加入纳米硅薄层作为空穴阻挡层,研究器件电致发光性质,实验结果表明器件的发光强度显著增强,并且发光效率较无纳米硅阻挡层的发光器件提高了80%以上.     

Dependence of Optical Absorption in Silicon Nanostructures on Size of Silicon Nanoparticles

The amorphous silicon nanoparticles (Si NPs) embedded in silicon nitride (SiN_x) films prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique are studied. From Raman scattering investigation, we determine that the deposited film has the structure of silicon nanocrystals embedded in silicon nitride (nc-Si/SiNx) thin film at a certain hydrogen dilution amount. The analysis of optical absorption spectra implies that the Si NPs is affected by quantum size effects and has the nature of an indirect-band-gap semiconductor. Further, considering the effects of the mean Si NP size and their dispersion on oscillator strength, and quantum-confinement, we obtain an analytical expression for the spectral absorbance of ensemble samples. Gaussian as well as lognormal size-distributions of the Si NPs are considered for optical absorption coefficient calculations. The influence of the particlesize-distribution on the optical absorption spectra was systematically studied. We present the fitting of the optical absorption experimental data with our model and discuss the results.     

氮化硅薄膜中硅纳米颗粒的形成机制研究

采用等离子体增强化学气相沉积技术,以SiH₄作为硅源, NH₃和N₂共同作为氮源,在单晶硅衬底上制备了不同的氮化硅薄膜. X射线衍射分析薄膜晶体结构,通过计算晶格尺寸大小证明了纳米硅颗粒的存在. 傅里叶变换红外光谱分析了薄膜中的键合作用的变化并结合化学反应过程对氮化硅薄膜中纳米硅颗粒的形成机制进行了研究,发现Si—Si键作为硅纳米颗粒的初始位置, 当反应朝着生成Si—Si的方向进行时,可以促进氮化硅薄膜中硅纳米颗粒的形成. X射线衍射分析和光致发光实验结果表明Si—Si键浓度增大时, 所形成的纳米硅颗粒的尺寸和浓度都随之增大.