退火温度对富硅氮化硅薄膜发光特性和结构的影响

采用直流等离子体增强化学气相沉积(PECVD)法在(100)单晶硅片表面生长富硅氮化硅薄膜,研究了不同的退火温度对氮化硅薄膜发光性质和结构的影响。研究发现,随着退火温度的升高,氮化硅薄膜的发光强度逐渐减弱,发光是由缺陷能级引起的,在900 ℃时荧光基本消失。XPS测试表明,在N₂氛围900 ℃下退火,氮化硅薄膜中未有硅相析出,故未表现出硅量子点的发光。FTIR测试也为PL结论提供了一定的证据。     

包含硅量子点的富硅SiNx 薄膜结构与发光特性

采用等离子体增强化学气相沉积法, 以NH₃与SiH₄为反应气体, n型单晶硅为衬底, 低温(220 ℃)沉积了富硅氮化硅(SiN_x)薄膜. 在N₂氛围中, 于500–1100 ℃ 范围内对样品进行了热退火处理. 采用Raman 光谱技术分析了薄膜内硅量子点的结晶情况, 结果表明, 当退火温度低于950 ℃时, 样品的晶化率低于18%, 而当退火温度升为1100 ℃, 晶化率增加至53%, 说明大部分硅量子点都由非晶态转变为晶态. 实验通过Fourier 变换红外吸收(FTIR)光谱检测了样品中各键的键合结构演变, 发现Si–N键和Si–H键随退火温度升高向高波数方向移动, 说明了薄膜内近化学计量比的氮化硅逐渐形成. 实验还通过光致发光(PL)光谱分析了各样品的发光特性, 发现各样品中均有5个发光峰, 讨论了它们的发光来源, 结合Raman光谱与FTIR光谱表明波长位于500–560 nm的绿光来源于硅量子点, 其他峰则来源于薄膜内的缺陷态. 研究了硅量子点的分布和尺寸对发光带移动的影响, 并根据PL峰位计算了硅量子点的尺寸, 其大小为1.6–3 nm, 具有良好的限域效应. 这些结果有助于制备尺寸不同的硅量子点和基于硅量子点光电器件的实现. 关键词： 硅量子点 氮化硅薄膜 光致发光 Fourier 变换红外吸收     

退火及溅射气氛对氮化硅薄膜光致发光的影响

利用射频磁控反应溅射方法制备富硅的氮化硅薄膜。衬底材料为抛光的硅片,靶材为硅靶,在Ar-N₂气环境下,通过改变两种气体的组分比来改变样品成分,并在高纯N₂气氛下对其进行高温退火处理。用X射线光电子能谱(XPS)和X射线衍射(XRD)对样品进行了表征,并测试了样品的光致发光谱 (PL)。实验结果表明：X射线光电子能谱中出现了Si—N键合结构,同时还有少量的Si—O键生成,通过计算得出Si/N比值约为1.51,制备出了富硅的氮化硅薄膜;薄膜未经退火前,在可见光区域没有观察到明显的光致发光峰,经过高温退火后,XRD中新出现的衍射峰证实了纳米硅团簇的生成,PL图谱中在可见光区域出现了光致发光峰的蓝移现象,结合XRD结果,用纳米晶的量子限域效应对上述现象进行了合理解释。     

室温下掺Er富硅氧化硅和掺Er富硅氮化硅的光致发光及其退火

用磁控溅射淀积掺Er氧化硅、掺Er富硅氧化硅、掺Er氮化硅和掺Er富硅氮化硅薄膜,室温下测量这四种薄膜的光致发光（PL）谱,观察到这四种薄膜都具有1.54μm的峰位,其强度与薄膜的退火温度有关。为了确定1.54μmPL的最佳退火温度,这些薄膜都分别在600,700,800,900,1000,1100℃的温度下同时退火,发现两种富硅薄膜的最佳退火温度是800℃,不富硅的两种薄膜的最佳退火温度是900℃。样品的1.54μmPL最强,且800℃退火的掺Er富硅氧化硅薄膜的1.54μm峰强度是最强的,比不富硅的强了约20倍,还观察到这四种薄膜都具有1.38μm的PL带,且掺Er富硅氧化硅和掺Er富硅氮化硅这两种薄膜的PL在强度上1.38μm峰与1.54μm峰有一定的关系。     

镶嵌有纳米硅的SiN_x薄膜光致发光的温度依赖特性研究

采用对靶磁控溅射法在单晶硅衬底上沉积镶嵌有纳米硅的氮化硅薄膜,然后在形成气体FG(10%H2,90%N2)气氛中进行450℃常规热退火50min。通过荧光光谱仪测得的稳态/瞬态光致发光(PL)谱研究了镶嵌有纳米硅的氮化硅(SiNx)薄膜样品光致发光特性。结果表明,样品的发光过程可以归因于纳米硅的量子限制效应发光和与缺陷相关的发光。随着激发光能量的增加,PL谱峰位发生蓝移,表明较小粒度的纳米硅发光比例增加;温度的降低会抑制非辐射复合过程,提高辐射复合几率,因此发光寿命延长,发光强度呈指数增加;随着探测波长的减小,样品的发光寿命则明显缩短,表明纳米硅的量子限制效应发光对温度有很强的依赖性。     

退火工艺对含硅量子点SiC_x薄膜光谱特性的影响

采用磁控共溅射法并结合微波退火和快速光热退火工艺,在不同退火温度下制备了含硅量子点的富硅SiC_x薄膜。采用掠入射X射线衍射(GIXRD)、拉曼光谱和光致发光(PL)光谱技术对薄膜进行了表征,研究了退火工艺对薄膜中硅量子点数量、尺寸、晶化率以及发光峰的影响。结果表明:与快速光热退火相比,微波退火不但能降低硅量子点的形成温度(降低200℃),而且还能降低β-SiC量子点的形成温度(降低100℃);在相同退火温度下,微波退火制备的硅量子点的数量更多、晶化率更高、光致发光峰更强;采用1000℃温度的微波退火样品的硅量子点数量最多、尺寸最大(5.26nm)、晶化率最高(74.25%)、发光峰最强,说明微波退火能凝析出高质量的硅量子点。     

氢等离子体气氛中退火多孔硅的表面和光荧光特性

用电化学腐蚀法制备了多孔硅(PS),在氢等离子体气氛中不同温度下对多孔硅样品进行了退火处理,并进行了光致发光(PL)谱和原子力显微镜(AFM)表面形貌的测量。不同退火温度给PS表面形态带来较大变化,也影响了其PL谱特性。在退火的样品中观察到的PL谱高效蓝光和紫光谱带,我们认为主要源于量子限制发光峰和非平衡载流子被带隙中浅杂质能级所俘获而引起的辐射复合所产生的。在420—450℃退火处理的多孔硅的PL谱上观察到了一个未见诸于报道的紫光新谱带(3．24eV,382nm),其发光机理有待于进一步研究。     

氮流量在高氢氛围中对富硅氮化硅薄膜材料结构及其发光特性的影响

采用等离子体增强化学气相沉积技术,以N₂掺入到SiH₄和H₂的沉积方式,分别在玻璃和N型单晶硅片(100)衬底上制备富硅氮化硅薄膜。通过紫外-可见光吸收光谱、傅里叶变换红外吸收光谱(FTIR光谱)、拉曼光谱和光致发光谱(PL谱)分别表征掺氮硅薄膜材料的带隙、结构及其发光特性的变化。结果表明：在氢气的氛围中,随着氮气流量的增加,氢原子能够对薄膜缺陷起到抑制作用,并使较低的SiH₄/N₂流量比下呈现富硅态,但却不利于硅团簇的形成。随着氮原子的掺入,Si—N键的含量增大,带隙增大,薄膜内微结构的无序度也增大,薄膜出现了硅与氮缺陷相关的缺陷态发光;随着氮原子进一步增加,出现了带尾态发光,进一步讨论了发光与结构之间的关联。这些结果有助于采用PECVD制备富硅氮化硅对材料发光与结构特性的优化。     

富硅氮化硅薄膜的荧光发射

室温下在3．45eV的激光激发下,对950℃温度下淀积的LPCVD富硅的SiNx薄膜中,观测到5个高强度的可见荧光的发射。其峰位位置分别为2．7,2．69,2．4,2．3,2．1eV。通过TEM、IR、XPS等的分析研究表明,该样品为纳米硅镶嵌结构的a-SiNx：H复合膜,分析了其微结构的成因及其与膜内应力之间的相互关系。经过1000～1200℃快速退火(RTA)处理,原PL谱蓝移并只出现了峰位为3．0,2．8eV的两个紫蓝色荧光的发射,用能隙态模型对此结果做了初步的分析和讨论。认为薄膜中纳米硅团簇的密度、尺寸的变化和亚稳态缺陷态对其PL峰以及膜应力起着十分重要的作用。     

ZnO∶V薄膜后退火处理前后的微结构与发光特性

利用溶胶-凝胶(Sol-gel)法在单晶硅(100)衬底上分别制备了ZnO∶V薄膜和纯ZnO薄膜。为进一步研究后退火对ZnO∶V薄膜结构和发光性质的影响,在两段式快速退火后又在800℃下进行了后退火处理。X射线衍射的结果表明:后退火处理前,钒(V)的掺入使ZnO结晶质量变差,而800℃退火处理后,从ZnO的衍射峰中可以看出,相对于无V杂样品其结晶质量变好。扫描电子显微镜形貌图中可以看出制备的样品薄膜颗粒大小均匀,薄膜致密度较高。光致发光(PL)谱的研究表明:ZnO∶V薄膜在800℃退火处理后,紫外和绿带发光峰均增强,但紫外发光峰增强得更多;与同样条件下制备的纯ZnO薄膜的PL谱比较,发现V掺杂后样品的紫外激子复合发光峰的强度明显增强且峰位发生蓝移,而缺陷引起的绿带发光峰的强度降低。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.