氧化多孔硅/聚合物复合膜的折射率

用Bruggeman模型理论,分析了氧化多孔硅/聚合物复合膜的等效折射率与多孔硅孔隙率、氧化度和嵌入率的关系.实验研究了嵌入PMMA材料的氧化多孔硅/聚合物膜的等效折射率.证实了在多孔硅中嵌入聚合物可使薄膜的光学参量保持稳定.     

硅的可见光发射—通向全硅光电子集成之途

由于Ｓｉ是一种禁带宽度只有１．１ｅＶ的间接带隙材料，其发光效率极低，因此长期以来Ｓｉ被认为是一种不可能用于制作可见光区光电器件的材料．但近一两年才出现的多孔硅光致发光现象，对人们的这种传统概念产生了巨大的冲击，一股多孔硅的研究热潮也正在兴起．本文将结合作者在多孔硅方面的工作，对多孔硅光致发光现象的研究背景、现状和潜在的应用作了较详细的介绍．     

利用共溅射方法实现硅基材料上的纳米Ge的可见光发射

如何实现硅基材料的发光,一直是很受重视的一个研究方向。以往是通过硅基外延生长直接带隙材料或锗硅超晶格的途径实现Si基材料发光。90年代初发倪的多孔硅发光[1],引起人们的广泛关注,对多孔硅的制备工艺、发光特性、机理和定性以及可能的应用等方面进行了广泛的研究。但至今尚没有阐明发光机理,而且多孔硅存在结构脆弱、对环境敏感、不易实现电注入等问题。     

多孔硅的光学非线性效应

自从1990年英国皇家信号与雷达研究所的Canham发现了多孔硅的可见光发射现象以后[1],在国际上掀起了一股多孔硅发光研究的热潮.继光致发光以后,有好几个研究组已观察到多孔硅的固态电致发光[2],这是向多孔硅在光电子器件的应用方向迈出的一大步.对于多孔硅的发光机理,虽然多数人倾向于认为这是一种量子线或量子点结构的限制效应,但也有一些与之相矛盾的实验结果,以致提出了一些其他的可能机理,如 SiH2或Si6O2H5聚合物,a-St,应变和杂质的作用等.所以要最终确定多孔硅的发光究竟是否是一种量子限制效应,还有待于提供进一步的实验事实. 另一…     

掺铒硅多孔化后的光致发光特性

采用一种新的方法制备掺Er多孔硅.首先通过分子束外延法生长Er,O共掺的硅外延层,然后通过常规的电化学阳极腐蚀法将外延层制备成掺Er离子的纳米硅柱结构.由于实现了Er离子在多孔硅中沿深度方向的均匀分布,得到峰宽仅6nm的Er3+本征发光.同时,由于铒与氧共掺于硅柱内部,多孔硅不再需要通过高温后处理引入氧来实现铒的光学激活.实验还对多孔化前后,Er3+的发光强度作出直观的比较,讨论多孔硅可见光及红外光区域的发光对Er3+红外发射的影响. 关键词：     

n型有序多孔硅基氧化钨室温气敏性能研究

利用电化学腐蚀方法制备了n型有序多孔硅, 并以此为基底用直流磁控溅射法在其表面溅射不同厚度的氧化钨薄膜. 利用X射线和扫描电子显微镜表征了材料的成分和结构, 结果表明, 多孔硅的孔呈柱形有序分布, 溅射10 min的WO₃薄膜是多晶结构, 比较松散地覆盖在整个多孔硅的表面. 分别测试了多孔硅和多孔硅基氧化钨在室温条件下对二氧化氮的气敏性能, 结果表明, 相对于多孔硅, 多孔硅基氧化钨薄膜对二氧化氮的气敏性能显著提高. 对多孔硅基氧化钨复合结构的气敏机理分析认为, 多孔硅和氧化钨薄膜复合形成的异质结对良好的气敏性能起到主要作用, 氧化钨薄膜表面出现了反型层引起了气敏响应时电阻的异常变化. 关键词： 有序多孔硅 氧化钨薄膜 二氧化氮 室温气敏性能     

多孔硅实验方法

多孔硅实验方法王兰芳，邓家干（陕西工学院汉中７２３００３）（广西农业大学南宁５３０００５）前言多孔硅（ＰｏｒｏｕｓＳｉｌｉｃｏｎＬａｇｅｒ，简称ＰＳＬ）是一种把单晶硅作为材料，通过各种方法使硅表面形成一层由大量垂直于表面的微孔（孔径为１—１００ｎｍ）...     

21世纪的光学和光电子讲座第二讲 硅基发光材料和器件研究

硅基发光材料和器件是实现光电子集成的关键。文章评述了目前取得较大进展的几种主要硅基发光材料和器件的研究,包括掺饵硅,多孔硅,纳米硅以及Ｓｉ／ＳｉＯ２等超晶格结构材料,展望了这些不同硅基发光材料作为发光器件和在光电集成中的发展前景。     

基于微结构参数建模的多孔硅绝热层热导率研究

多孔硅由于具有较低的热导率,因而可以将其作为半导体器件中的绝热层.与其他从边界散射等复杂微观热传导机制出发建模研究多孔硅的热导率不同,将多孔硅热导率影响机制更表观地归结到孔洞的存在和分布等结构因素上,把整个多孔硅视为由硅连续材料介质和孔洞连续介质通过串联和并联组合成的复合微结构,给予其低热导率一个更为易于理解和简化的解释.进一步把孔隙率对等效热导率的影响分解为两个不同的部分,即纵向部分和横向部分,半定量地给出不同的孔洞结构和分布下孔隙率与等效热导率的关系.与实验数据进行对比后验证了模型的有效性.继而从结构的角度说明了多孔硅热导率较低的原因.     

多孔硅结构与发光机理的非线性光学研究

最近的研究中,采用1.06μm超短脉冲光激发,在多孔硅表面观察到了有效的红外多光子激发的荧光发射.研究表明,这是一个增强的三阶非线性光学过程.本文利用其三阶非线性特性对具有强可见光发射的多孔硅结构进行了研究,结果显示晶体硅的各向异性特征在多孔硅中几乎被保留;此外,较强的激光激发导致的红外上转换荧光信号衰减过程被归结为与多孔硅表面氢的脱附有关.     

Local chemical states and microstructure of photoluminescent porous silicon studied by means of EELS and TEM

Photoluminescent porous Si (PS) layers were formed on low resistivity p-type Si(100) wafers by anodization at a current density (Ia) of 100-350 mA cm(-2) at room temperature. The local chemical states and the microstructures of the PS layers were studied by means of electron energy loss spectroscopy (EELS) and transmission electron microscopy (TEM), and were correlated to the red photoluminescence (PL). The PS layer consists of sponge-like and tree-like structures. The tree-like structure becomes finer with increase of Ia. The fine tree-like structure is shown to be favorable for intensive PL. The EELS analysis reveals that the Si-4O structure, namely the basic structure of SiO2, and Si crystals coexist in the PS layers. The relative content of SiO2 to Si crystallites (R) increases with increase in Ia and decreases with the depth from the top surface of the PS layer. High R corresponds to intensive PL. These results suggest that PL may be connected with some kind of defects in SiO2 and/or defects in the boundary between Si crystallites and SiO2 structure in anodized PS layers, and that PL may be mainly emitted from the layer near the top surface of the PS layers.     

少子寿命和表面形貌与多孔硅发光性能的关系

研究了不同时间腐蚀的多孔硅的光致发光性能与多孔硅的表面形貌和少子寿命之间的关系。结果表明,多孔硅的发光来自与氧空位有关的缺陷,而多孔硅表面的氢原子能够钝化多孔硅表面的非辐射中心从而提高多孔硅的发光效率。多孔硅的空隙度随腐蚀时间的延长而增大,这也导致了多孔硅的少子寿命的降低,从而造成多孔硅的光致发光效率随多孔硅空隙度的增大以及少子寿命的降低而提高。另外,原子力显微照片表明长时间的腐蚀使多孔硅表面层被化学腐蚀,从而降低了多孔硅表面的粗糙度。     

激光促进多孔硅内表面氧化与光致发光的退化

本文对刚制备的以及分别经以下三种情况:1.样品在1大气压的氧气中经激光(Ar~+激光器的48.80nm线,功率密度为1.77W/cm~2)连续照射1小时;2.样品在1大气压的氧气中在没有激光照射的情况下保持1小时;3.样品在1.3×10~2Pa真空度下用激光连续照射1小时处理后的多孔硅在室温下进行了光致发光谱和傅里叶变换红外吸收测量,研究了处理前后光谱的变化。实验发现经第一种情况处理后光致发光峰位蓝移了约0.1eV,发光强度衰减了二十几倍,相应的其红外光谱中与氧有关的吸收峰强度大幅度增长,而经第二,三两种情况处理后它们的光致发光及红外吸收谱则无大的变化。研究表明在氧气中激光辐照能大大加速多孔硅内表面的氧化。我们认为很可能是多孔硅内表面的氧化作用使光致发光峰位蓝移,由氧化作用产生的非辐射复合中心导致光致发光效率的下降。     

热退火、激光束和电子束等作用对纳米硅制备及其局域态发光特性的影响

在纳米晶体硅制备的过程中, 晶化处理是影响和提高纳米硅发光效率的重要制备环节. 热退火、激光退火和电子束辐照是使纳米硅样品晶化的不同方式. 实验表明: 选取适当的晶化方式和参量对制备纳米硅晶体结构至关重要, 特别是在制备硅量子点和量子面的过程中控制好参量, 可以得到较高的发光效率. 有趣的是, 在实验中发现: 当晶化时间较短(如低于20 min)时, 可以获得较好的纳晶硅结构(如量子点结构), 对应于较好的纳晶硅光致发光(PL)和掺杂局域态发光; 当晶化时间较长(如超过30 min)时, 纳米晶体硅结构被破坏, 致使PL谱逐渐减弱与消失. 结合热退火、激光退火和电子束辐照对纳米硅晶化过程, 本文建立起晶化时间对纳米硅局域态发光影响机理的物理模型, 解释了晶化时间对纳米硅局域态发光的影响.     

Optoelectronic characterization of ZnS/PS systems

ZnS thin films are deposited on porous silicon （PS） substrates with different porosities by pulsed laser deposition （PLD）. The photoluminescence （PL） spectra of the samples are measured at room temperature. The results show that the PL intensity of PS after deposition of ZnS increases and is associated with a blue shift. With the increase of PS porosity, a green emission at about 550 nm is observed in the PL spectra of ZnS/PS systems, which may be ascribed to the defect-center luminescence of ZnS films. Junction current- voltage （I-V） characteristics were studied. The rectifying behavior of I-V characteristics indicates the formation of ZnS/PS heterojunctions, and the forward current is seen to increase when the PS porosity is increased.     

Dynamic photoluminescence lifetime imaging for the characterisation of silicon wafers

We present a fast and calibration‐free carrier lifetime imaging technique based on photoluminescence (PL) measurements using an InGaAs camera for the examination of crystalline silicon wafers. The carrier lifetime is determined from the time dependent luminescence emission after optical excitation. A ratio, including four PL images acquired at different times during the modulated excitation, is calculated and found to depend only on the camera integration time and the effective carrier lifetime. Therefore, the carrier lifetime is unambiguously determined by this ratio without knowing any additional wafer parameter. We demonstrate the applicability of the dynamic PL technique to multicrystalline silicon wafers. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Emission mechanisms in stabilized iron-passivated porous silicon: Temperature and laser power dependences

Photoluminescence (PL) measurements of porous silicon (PS) and iron-porous silicon nanocomposites (PS/Fe) with stable optical properties versus temperature and laser power density have been investigated. The presence of iron in PS matrix is confirmed by Raman spectroscopy. The PL intensity of PS and PS/Fe increases at low temperature, the evolution of integrated PL intensity follows the modified Arrhenius model. The incorporation of iron in PS matrix reduces the activation energy traducing the existence of shallow levels related to iron atoms. Also, the temperature dependence of the porous silicon PL peak position follows a linear evolution at high temperature and a quadratic one at low temperature. Such evolution is due to the thermal carriers' redistribution and an energy transfer. Similarly, we have compared the laser power dependence of the PL in PS and PS/Fe layers. The results prove that the recombination process in PS is realised through the lower energy traps localised in the electronic gap. However, the observed emission in PS/Fe is essentially due to direct transitions. So, we can conclude that the presence of iron in PS matrix induces a strong modification of the PL mechanisms.     

Formation of luminescent (NH4)2SiF6 phase from vapour etching-based porous silicon

In this paper we describe the formation of a luminescent (NH₄)₂SiF₆ via porous silicon (PS) obtained from HNO₃/HF vapour etching (VE) silicon (Si) substrates. It was found that at specific conditions, PS transforms in a luminescent thick white powder (WP) layer. Scanning electron microscopy (SEM) revealed that the WP has a coral-like structure. It was also found that PS persists as an intermediate layer between the Si substrate and the WP, and seems to be the seed that transforms into the WP. SEM microanalysis show that the WP is essentially composed of silicon (Si), nitrogen (N) and fluorine (F). Fourier transform infrared (FTIR) spectroscopy investigations show that this WP contains SiF₆²⁻ and NH₄⁺ ions and N---H chemical bonds. X-ray diffraction (XRD) patterns of the WP confirm that a (NH₄)₂SiF₆ cubic phase is concerned. SEM microanalyses show an excess of Si in the WP matrix. FTIR spectroscopy and XRD analysis reveal the presence of crystalline Si particles and SiO_x, both originating from the excess of Si. The (NH₄)₂SiF₆ WP phase emits an intense photoluminescence (PL) band, shifted towards higher energies as compared to the starting PS layer. The possible origin and mechanism of the luminescence emission was discussed taking into account the ability of small SiO_x-surrounded Si particles to emit PL at rather high energy. The wide range variation of the thickness of the (NH₄)₂SiF₆ WP may be easily used for the grooving of Si wafers.     

Low temperature N2-based passivation technique for porous silicon thin films

A technique is presented for the passivation of porous silicon (PS) thin films via nitrogen based annealing at the lowest temperature ever reported. Annealing freshly anodized PS thin films at temperatures as low as 520  ^°C under N₂ flow in a rapid thermal annealer produces films that show no change in refractive index when exposed to ambient conditions over 60 days. These films also exhibited chemical resistance by surviving a brief dip in both concentrated KOH and buffered HF. Unlike most other PS surface passivation methods, this technique causes negligible reduction in refractive index of the annealed PS thin films. Passivation only occurs when dangling bonds and mono-hydrides populate the PS surface, providing a path for thermal interactions with the N₂ gas.     

Localized electronic states in gaps on hole-net structures of silicon

Hole-net structure silicon is fabricated by laser irradiation and annealing, on which a photoluminescence (PL) band in a the region of 650--750~nm is pinned and its intensity increases obviously after oxidation. It is found that the PL intensity changes with both laser irradiation time and annealing time. Calculations show that some localized states appear in the band gap of the smaller nanocrystal when Si=O bonds or Si--O--Si bonds are passivated on the surface. It is discovered that the density and the number of Si=O bonds or Si--O--Si bonds related to both the irradiation time and the annealing time obviously affect the generation of the localized gap states of hole-net silicon, by which the production of stimulated emission through controlling oxidation time can be explained.