激光作用于单晶硅样品后的强荧光效应

将功率为75W、波长为1064nm的YAG激光束照射在单晶硅样品上,形成的孔状结构有很特殊的表面形貌.特别是在孔内的侧壁上,有很特殊的网孔形结构,这里有很强的受激荧光发光效应,光致荧光谱峰在710nm处.本文中介绍了单纯激光加工生成多孔硅和纳晶硅样品的方法,观察和分析了样品中的低维纳米结构、氧化分布及其发光特性,特别注意到样品孔洞中的侧壁上的网孔形结构的强荧光效应.我们用量子受限效应结合硅晶与氧化硅界面态复合的综合模型来解释其光致发光的增强机理.     

激光作用生成的网孔硅结构

作者结合量子受限效应,提出纳硅晶与氧化硅界面态发光模型来解释激光作用生成的纳米网孔壁结构的强荧光效应。将功率为50W、波长为1064nm的YAG激光束(束斑直径0.05mm)照射在硅样品表面打出小孔,在孔内的侧壁上,有很特殊的网孔形结构,其中的网孔壁厚为纳米尺度,这里有很强的受激荧光发光效应,发光峰中心约在700nm处。我们将激光与硅样品的作用隔离于无氧化的环境里,分别比较了将硅样品浸入酒精、氢氟酸和水中的激光加工结果,其发光情况证实了该发光模型的真实性。优化激光加工的条件,我们获得了较强发光的样品。     

激光作用生成的纳晶硅与氧化硅界面态发光模型

我们结合量子受限效应,提出纳硅晶与氧化硅界面态发光模型来解释激光作用生成的纳米网孔壁结构的强荧光效应.将功率为50W、波长为1 064nm的YAG激光束(束斑直径0.05mm)照射在硅样品表面打出小孔,在孔内的侧壁上,有很特殊的网孔形结构,其中的网孔壁厚为纳米尺度,这里有很强的受激荧光发光效应,发光峰中心约在700nm处.我们将激光与硅样品的作用隔离于无氧化的环境里,分别比较了将硅样品浸入酒精、氢氟酸和水中的激光加工结果,其发光情况证实了该发光模型的真实性.优化激光加工的条件,我们获得了较强发光的样品.     

激光辐照单晶硅样品的研究

将功率为30W、波长为1064nm的YAG激光束(束斑直径0.045mm)照射在硅样品表面打出小孔,在孔内的侧壁上有很特殊的网孔状结构,其中的网孔壁厚为纳米尺度,解释孔侧壁网孔状结构的机理.孔侧壁上的网孔状结构有很强的受激荧光发光效应,发光峰中心约在700nm处.当样品在加工和检查过程中保持脱氧状态时,其样品几乎没有发光,证实了氧在PL发光增强上起着重要作用.我们用量子受限及其纳晶与氧化硅界面态复合的综合模型来解释其光致发光的增强机理     

纳秒激光加工生成网孔硅的发光

我们分别在氧气、氮气或空气等不同氛围中用纳秒脉冲激光在硅基上加工生成网孔结构,发现这些样品有增强的PL发光,且各样品的PL峰很相似。通过第一性原理计算,发现各种网孔结构表面的成键类型与密度是形成PL发光增强的关键,并由此提出相应的物理模型。     

退火对硅锗薄膜上低维结构的PL光谱的影响

采用激光辐照的方法在硅锗薄膜样品表面生成微米级小孔,用高精度扫描电镜观察孔内结构,发现片状的纳米结构. 用荧光光谱仪测其光致荧光谱,在705 nm处出现较强的光致荧光谱（PL）. 对片状结构在800 ℃下进行退火20 min后,其PL光谱明显蓝移至575 nm. 退火40 min后,在725 nm处有较宽的PL光谱,同时,在606 nm处有一尖锐的PL光谱. 利用量子受限和纳晶与氧化物的界面态综合模型解释PL光谱的产生.     

基于线结构光的复杂深孔内轮廓三维测量方法

为了对孔内轮廓参数进行快速高精度测量,建立了一种基于线结构光的复杂深孔内轮廓三维测量系统.介绍了系统构成及测量原理、数学模型建立以及孔内截面轮廓尺寸计算方法.提出形态学光条细线化与灰度重心法相结合提取亚像素光条中心线算法.应用该系统对直径φ130.0 mm的复杂孔内轮廓进行实验,测量长度70 mm时,阳线圆直径测量误差为±32 μm,阴线圆直径测量误差为±54 μm.      

圆锥形小孔内等离子体的反韧致辐射吸收研究

在假设小孔为圆锥形的基础上，按照几何光学理论，通过跟踪光线在小孔内的多次反射轨迹，对激光深熔焊接小孔内等离子体的反韧致辐射吸收进行了详细研究．计算了小孔孔壁通过孔内等离子体的反韧致辐射吸收的激光功率密度，分析研究了孔壁的多次反射次数、圆锥形小孔的锥项角以及圆锥形小孔的直径等因素对孔壁上的激光功率密度分布的影响．通过比较小孔内等离子体的反韧致辐射吸收的激光功率密度和小孔孔壁上的多次反射吸收的激光功率密度，分析了两种能量吸收机制在小孔形成和维持过程中所起的不同作用．     

纳秒激光加工生成硅量子点的发光性质研究

该文报道氧气、氮气或空气等不同氛围中用纳秒脉冲激光在硅基上加工生成量子点结构,发现这些样品在700 nm波长附近均有增强的光致发光(Photoluminescence,PL),且各样品的PL峰很相似;经适当退火处理后,在某些样品上观察到随机受激发光.通过第一性原理计算,发现各种量子点结构表面的成键类型与密度是形成PL发光增强的关键,并由此提出相应的物理模型.     

Al掺杂4H-SiC第一性原理计算及二次离子质谱分析

本文采用基于密度泛函理论的第一性原理计算,使用CASTEP软件建立了4H-SiC重掺杂模型,对通过激光辐照固态Al膜制备的p型重掺杂4H-SiC薄膜的晶体结构和电子结构进行了计算分析,研究获得不同浓度Al掺杂4H-SiC的能带结构和态密度.结果表明,随着Al原子掺杂浓度的增大,辐照样品禁带宽度随之减小,费米能级进入价带,体现出p型半导体的特征.结合二次离子质谱测试分析,得到Al掺杂浓度随辐照层深度的变化规律,Al掺杂浓度在30 nm范围内较为均匀,约为1×10^20cm^-3.证明KrF准分子激光可以实现4H-SiC之Al原子重掺杂,随着深度的增加,激光能量密度逐渐降低,4H-SiC内Al原子掺杂浓度相应降低.验证了激光辐照Al膜掺杂所制备4H-SiC样品的p型半导体特征,得到了Al掺杂浓度随激光辐照深度的变化规律.     

A continuous-wave Raman silicon laser

Achieving optical gain and/or lasing in silicon has been one of the most challenging goals in silicon-based photonics because bulk silicon is an indirect bandgap semiconductor and therefore has a very low light emission efficiency. Recently, stimulated Raman scattering has been used to demonstrate light amplification and lasing in silicon. However, because of the nonlinear optical loss associated with two-photon absorption (TPA)-induced free carrier absorption (FCA), until now lasing has been limited to pulsed operation. Here we demonstrate a continuous-wave silicon Raman laser. Specifically, we show that TPA-induced FCA in silicon can be significantly reduced by introducing a reverse-biased p-i-n diode embedded in a silicon waveguide. The laser cavity is formed by coating the facets of the silicon waveguide with multilayer dielectric films. We have demonstrated stable single mode laser output with side-mode suppression of over 55 dB and linewidth of less than 80 MHz. The lasing threshold depends on the p-i-n reverse bias voltage and the laser wavelength can be tuned by adjusting the wavelength of the pump laser. The demonstration of a continuous-wave silicon laser represents a significant milestone for silicon-based optoelectronic devices.     

Conversion of silicon carbide to crystalline diamond-structured carbon at ambient pressure

Synthetic diamond is formed commercially using high-pressure, chemical-vapour-deposition and shock-wave processes, but these approaches have serious limitations owing to low production volumes and high costs. Recently suggested alternative methods of diamond growth include plasma activation, high pressures, exotic precursors or explosive mixtures, but they suffer from very low yield and are intrinsically limited to small volumes or thin films. Here we report the synthesis of nano- and micro-crystalline diamond-structured carbon, with cubic and hexagonal structure, by extracting silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1,000 degrees C. The presence of hydrogen in the gas mixture leads to a stable conversion of silicon carbide to diamond-structured carbon with an average crystallite size ranging from 5 to 10 nanometres. The linear reaction kinetics allows transformation to any depth, so that the whole silicon carbide sample can be converted to carbon. Nanocrystalline coatings of diamond-structured carbon produced by this route show promising mechanical properties, with hardness values in excess of 50 GPa and Young's moduli up to 800 GPa. Our approach should be applicable to large-scale production of crystalline diamond-structured carbon.     

Mechanism of hydrogen-induced crystallization of amorphous silicon

Hydrogenated amorphous and nanocrystalline silicon films manufactured by plasma deposition techniques are used widely in electronic and optoelectronic devices. The crystalline fraction and grain size of these films determines electronic and optical properties; the nanocrystal nucleation mechanism, which dictates the final film structure, is governed by the interactions between the hydrogen atoms of the plasma and the solid silicon matrix. Fundamental understanding of these interactions is important for optimizing the film structure and properties. Here we report the mechanism of hydrogen-induced crystallization of hydrogenated amorphous silicon films during post-deposition treatment with an H(2) (or D(2)) plasma. Using molecular-dynamics simulations and infrared spectroscopy, we show that crystallization is mediated by the insertion of H atoms into strained Si-Si bonds as the atoms diffuse through the film. This chemically driven mechanism may be operative in other covalently bonded materials, where the presence of hydrogen leads to disorder-to-order transitions.     

Optical gain in silicon nanocrystals

Adding optical functionality to a silicon microelectronic chip is one of the most challenging problems of materials research. Silicon is an indirect-bandgap semiconductor and so is an inefficient emitter of light. For this reason, integration of optically functional elements with silicon microelectronic circuitry has largely been achieved through the use of direct-bandgap compound semiconductors. For optoelectronic applications, the key device is the light source--a laser. Compound semiconductor lasers exploit low-dimensional electronic systems, such as quantum wells and quantum dots, as the active optical amplifying medium. Here we demonstrate that light amplification is possible using silicon itself, in the form of quantum dots dispersed in a silicon dioxide matrix. Net optical gain is seen in both waveguide and transmission configurations, with the material gain being of the same order as that of direct-bandgap quantum dots. We explain the observations using a model based on population inversion of radiative states associated with the Si/SiO2 interface. These findings open a route to the fabrication of a silicon laser.     

基于纳米复合材料的太赫兹滤波器研究

为了克服高阻硅片过低的太赫兹透过率和激光阈值,通过放电等离子体烧结(SPS)工艺制备了一种新型纳米复合材料,可以作为透过太赫兹波、隔离飞秒激光的高效太赫兹滤波器件.器件整体设计原理主要基于瑞利散射,粒径100nm左右的纳米颗粒可以选择性地使太赫兹波高效透过,透过率最多达90%,远超高阻硅片50%的透过率,并且可以散射掉大部分波长为800nm的高能激光.器件由太赫兹频段吸收率很低的金刚石纳米颗粒和真空球磨得到的高阻硅颗粒组成,金刚石的高熔点提高了激光阈值,疏松多孔的结构进一步减少了太赫兹波段菲涅尔反射损失,器件整体性能优异.     

叠层太阳电池中不同基质硅量子点的特性研究

叠层太阳电池的多能带结构设计可以有效提高太阳电池的转换效率,但是这种电池在实际制备过程中常会遇到低效率、高成本等问题。以提高效率为目的,在叠层太阳电池中引入具有量子效应的硅量子点是目前新型太阳电池研究的一大热点。文章对不同基质中硅量子点的能带模型进行了理论分析,介绍了硅量子点在几种不同基质中的形成方法及其相关性质的最新研究结果,并对比研究了SiO2、Si3N4和SiC用作硅量子点生长基质的优势与不足。     

p-i-n型非晶硅薄膜电池p层材料制备及光学性能研究

采用射频等离子体增强化学气相沉积(RF-PECVD)方法制备非化学计量比氢化非晶碳化硅(a-SiC:H)薄膜材料,借助紫外可见(UV-Vis)光谱、激光拉曼(Raman)光谱和傅里叶变换红外(FTIR)光谱等手段,研究了p-i-n型非晶硅(a-Si:H)薄膜太阳能电池p层a-SiC:H薄膜材料的制备与光学性能.研究结果表明甲烷和硅烷掺杂比能影响a-Si:H薄膜成键情况,而射频功率一定程度上能影响薄膜沉积速率,该研究结果可为制备转换效率高、性能稳定的p-i-n型非晶硅薄膜太阳能电池提供支持.     

激光支持等离子体爆轰波流场研究

采用高速纹影摄影法记录激光支持等离子体爆轰波流场的演化,得到流场冲击波阵面形状和尺寸随时间变化规律。建立激光支持等离子体爆轰波流场演化的物理模型,采用计算流体力学方法模拟计算激光击穿空气后,激光作用时间内及激光作用结束后等离子体流场演化过程。结果表明,纹影摄影法能有效观测到激光支持等离子体爆轰波的传播情况。等离子体爆轰波在激光作用初期为椭球形,随着时间的增加逐渐转变为球形。计算的等离子体爆轰波流场密度分布图与实验结果基本吻合。