Light emission from porous silicon

Room-temperature visible luminescence observed in porous silicon is one of the most significant discoveries of this decade as it opens up the possibility of silicon-based optoelectronics afresh. The exact mechanism of this different luminescence behaviour of porous silicon, compared to crystalline silicon, is not well established. In this paper results of a combination of infrared absorption, and photoluminescence emission and excitation spectroscopies will be described to show that the nanocrystallite nature of porous silicon and chemical environment at the surface are the important aspects of this novel luminescence behaviour.     

与标准集成电路工艺兼容的硅基光学器件研究

着重介绍了与标准集成电路工艺兼容的硅基光学器件的最新研究进展,包括硅基光发射器、硅基光波导和调制器件、硅基光电探测器和接收机以及硅基光电子集成回路的工作原理、制作工艺和集成技术.与标准集成电路工艺兼容的硅基光电子集成回路能有效地解决电互连芯片内部串扰、带宽和能耗等问题,并能够充分利用现有成熟的集成电路工艺,实现大规模生产,具有广阔的实用前景.     

High-yield plasma synthesis of luminescent silicon nanocrystals

Light emission from silicon based on quantum confinement in nanoscale structures has sparked intense research into this field ever since its discovery about 15 years ago. A barrier to the widespread utilization of luminescent silicon nanocrystals in such diverse application areas as optoelectronics, solid-state lighting for general illumination, or fluorescent agents for biological applications has been the lack of a simple, high-yield synthesis approach. Here we report a scaleable single-step synthesis process for luminescent silicon nanocrystals based on a low-pressure nonthermal plasma.     

Application of nanostructured porous silicon in the field of optics. A review

Porous silicon nanostructures have attracted a great deal of interest during the past few years, due to their many remarkable properties. The high-efficiency visible photo- and electro-luminescence of this material opened the way to the development of silicon-based optoelectronic devices fully compatible with standard industry processes. In addition to these luminescent properties, nanostructured porous silicon shows a variety of other interesting properties, including tunable refractive index, low light absorption in the visible, high internal surface, variable surface chemistry, or high chemical reactivity. All these properties, along with its ease of fabrication and the possibility of producing precisely controlled layered structures make this material adequate for its use in a wide range of fields, such as optics, micro- and optoelectronics, chemical sensing or biomedical applications, for example. This article reviews the applications of nanostructured porous silicon that exploit its unique optical properties, as in the case of light emitting devices, filtered photodetectors, optical sensors, and others.     

Light emission in silicon nanostructures

The many and diverse approaches to materials science problems have greatly enhanced our ability in recent times to engineer the physical properties of semiconductors. Silicon, of all semiconductors, underpins nearly all microelectronics today and will continue to do so for some time to come. However, in optoelectronics and, more recently, in photonics, the severe disadvantage of an indirect band gap has limited the application of elemental silicon. Here we review a number of diverse approaches to engineering efficient light emission in silicon nanostructures. These different approaches are placed in context and their prospects are assessed for applications in silicon-based photonics.     

HRTEM analysis of the nanostructure of porous silicon

The nanometric structure of porous silicon makes this material to be very suitable for its use in many different fields, including optoelectronics and biological applications. In the present work, the structure of porous silicon was investigated in detail by means of cross-sectional high-resolution transmission electron microscopy and digital image processing, together with electron energy loss spectroscopy. The structure of the Si/porous silicon interface and that of the silicon nanocrystals that compose porous silicon have been analyzed in detail. A strong strain contrast in the Si/porous silicon interface caused by high stresses was observed. Accordingly, dislocation pairs are found to be a possible mechanism of lattice matching between porous silicon and the Si substrate. Finally, high relative concentration of oxygen in the porous silicon layer was observed, together with low relative electron concentration in the conduction band when compared to Si.     

Optical and electrical properties of thin carbide-containing films on silicon

The optical and electrical properties of thin carbide-containing films grown using a new promising method on silicon wafers have been experimentally studied. The results of electron diffraction measurements, the current-voltage characteristics measured in the dark and under illumination, the photo emf as a function of the excitation level, and the photoresponse spectrum are presented. The proposed thin-film system is a promising material for optoelectronics.     

Synthesis and oxidation of luminescent silicon nanocrystals from silicon tetrachloride by very high frequency nonthermal plasma

Silicon nanocrystals have recently attracted significant attention for applications in electronics, optoelectronics, and biological imaging due to their size-dependent optical and electronic properties. Here a method for synthesizing luminescent silicon nanocrystals from silicon tetrachloride with a nonthermal plasma is described. Silicon nanocrystals with mean diameters of 3-15 nm are synthesized and have a narrow size distribution with the standard deviation being less than 20% of the mean size. Control over crystallinity is achieved for plasma pressures of 1-12 Torr and hydrogen gas concentrations of 5-70% through adjustment of the plasma power. The size of nanocrystals, and resulting optical properties, is mainly dependent on the gas residence time in the plasma region. Additionally the surface of the nanocrystals is covered by both hydrogen and chlorine. Oxidation of the nanocrystals, which is found to follow the Cabrera-Mott mechanism under ambient conditions, is significantly faster than hydrogen terminated silicon due to partial termination of the nanocrystal surface by chlorine.     

Development of interference filters based on multilayer porous silicon structures

Porous silicon (PS) has a great potential in optical applications due to its tuneable refractive index. In particular, multilayer structures consisting of alternating PS layers with different refractive indices can be used as interference filters for applications in the field of optoelectronics and sensors. In the present work, the optical properties of PS single layers and multilayer structures were studied. Since the refractive index of PS varies depending on the air content of the porous matrix, the PS structures were modelled as an homogeneous mixture of silicon and air, according to the effective medium theories (EMTs). By adjusting the refractive index and thickness of each individual layer, we can obtain a stack of PS layers with the desired optical properties, resulting in interference filters of predetermined bandwidth.     

Evaporation and deposition of alkyl-capped silicon nanocrystals in ultrahigh vacuum

Nanocrystals are under active investigation because of their interesting size-dependent properties and potential applications. Silicon nanocrystals have been studied for possible uses in optoelectronics, and may be relevant to the understanding of natural processes such as lightning strikes. Gas-phase methods can be used to prepare nanocrystals, and mass spectrometric techniques have been used to analyse Au and CdSe clusters. However, it is difficult to study nanocrystals by such methods unless they are synthesized in the gas phase. In particular, pre-prepared nanocrystals are generally difficult to sublime without decomposition. Here we report the observation that films of alkyl-capped silicon nanocrystals evaporate upon heating in ultrahigh vacuum at 200 degrees C, and the vapour of intact nanocrystals can be collected on a variety of solid substrates. This effect may be useful for the controlled preparation of new quantum-confined silicon structures and could facilitate their mass spectroscopic study and size-selection.     

Predictions of novel nanostructures of silicon by metal encapsulation

Recent studies using ab initio total energy calculations have shown exciting possibilities of developing novel metal encapsulated caged clusters of silicon with fullerene-like, Frank–Kasper and other polyhedral structures. In contrast to carbon for which empty cage fullerene structures are stable with 20 or more atoms, 10–16 atom silicon cage structures are stabilized by a guest metal atom. These nanoclusters are predicted to exhibit luminescence in the visible range and could find applications in biological systems, optoelectronics, and as tagging material. The Raman and infrared spectra have been calculated and they could help in the experimental identification of the structures. Interaction of these clusters with metal as well as oxygen or hydrogen atoms show that the fullerene structure is stable. Also the interaction between clusters themselves is weak and the ionization potentials, large. These properties make them attractive for cluster assembled materials such as nanowires, nanotubes, and other 2 and 3D structures. Studies on hydrogen interaction have led to the predictions of empty center hydrogenated silicon fullerenes Si_nH_n with large HOMO–LUMO gaps. These could further be doped endohedrally or exohedrally to produce novel silicon fullerenes with a variety of properties opening new ways of using silicon for diverse applications.     

熔析结晶法提纯硅工艺研究进展

随着光伏产业的快速发展,对太阳能级硅原材料的需求不断增加。熔析结晶法作为一种冶金硅提纯的新工艺越来越受到重视。熔析结晶法是利用冶金硅中杂质元素的偏析行为,选择适当的熔析介质,使杂质元素从冶金硅中偏析到熔析介质中,进而获得高纯硅的方法。详细介绍了Al-Si、Sn-Si、Cu-Si、Fe-Si和Ca-Si等熔析体系对冶金硅提纯的研究现状,比较了各种介质体系的优缺点。同时针对熔析结晶法提纯硅存在的问题提出了一些建议。     

精炼法提纯冶金硅至太阳能级硅的研究进展

随着光伏市场需求不断增加,满足光伏电池技术经济指标要求的硅材料出现严重短缺,低成本提纯冶金硅至太阳能级硅工艺技术越来越受到广泛重视,成为研究开发热点.综述了近年来国外有关基于定向凝固原理开发的精炼法提纯冶金硅至太阳能级硅的技术成果,并进行了比较分析,展望了应用前景.     

纳米粒子自组装无机硅/有机硅复合功能膜技术

采用自组装法对纳米粒子表面进行修饰,修饰效果表明:控制了纳米粒子的表面态,使纳米粒子稳定化;赋予纳米粒子无机硅/有机硅复合功能膜,使纳米粒子适用性广、高性能、多功能;不仅扩大了在传统产业中的应用范围,而且还可作为纳米结构的结构单元,用于自组装纳米功能器件等纳米结构材料.文中介绍了这一技术的原理、工艺、修饰效果以及特点.     

硅薄膜中的结构缺陷研究进展

硅薄膜作为制备硅薄膜太阳电池的重要材料,得到了广泛研究和应用,而硅薄膜中的各种缺陷及缺陷密度则对薄膜电池的转换效率和稳定性有着至关重要的影响。对硅薄膜中的缺陷种类、缺陷研究方法以及缺陷对薄膜性能的影响进行总结,期望对提高和改善硅薄膜质量乃至硅薄膜太阳电池转换效率和稳定性提供一定的指导。     

Size-tunable infrared (1000–1600 nm) electroluminescence from solution-processible PbS quantum dot nanocrystals: Towards monolithic optoelectronic integration on silicon

Abstract

This article reviews devices fabricated using room-temperature solution-casting compatible with silicon post-processing, which produce communications-wavelength electroluminescence. Integrable optoelectronics may be facilitated in this processible material system-one which may conveniently be combined with silicon electronics, passive optics, and RF platforms. Synthetic conditions determine nanocrystal diameter and thereby tune, through the quantum size effect, the spectrum of optical emissions from the quantum dots. It is shown that it is possible to span across and beyond the 1.3–1.6 μm spectrum of optical communications. Nonradiative recombination from the nanocrystals' surface is addressed by choosing stabilizing, passivating organic ligands which nevertheless permit energy transfer from polymer to nanocrystals. Experimental determination of the efficiency of excitation transfer from the polymer matrix to dots, a key factor in increasing device electroluminescence efficiency, is described.     

Design of porous silicon/PECVD SiOx antireflection coatings for silicon solar cells

The meso-porous silicon (PS) has become an interesting material owing to its potential applications in many fields, including optoelectronics and photovoltaics. PS layers were grown on the front surface of the n⁺ emitter of n⁺-p mono-crystalline Silicon junction. The thickness and the porosity of the PS layer were determined by an ellipsometer, as a function of time duration of anodization, and the variation law of the PS growth kinetics is established. Single layers PS antireflection coating (ARC) achieved around 9% of effective reflectivity in the wavelength range between 400 and 1000 nm on junction n⁺-p solar cells. To reduce the reflectivity and improve the stability and passivation properties of PS ARC, silicon oxide layers were deposited by PECVD on PS ARC. SiO_x layers of thickness of 105 nm combined with PS layer led to 3.8% effective reflectivity. V_oc measurements were carried out on all the samples by suns-V_oc method and showed an improvement of the quality of the passivation brought by the oxide layer. Using the experimental reflectivity results and taking into account the passivation quality of the samples, the PC1D simulations predict an enhancement of the photogenerated current exceeding 44%.     

Thermo-mechanical and fracture properties in single-crystal silicon

Single-crystal silicon is extensively used in the semiconductor industry. Even though most of the steps during processing involve somehow thermo-mechanical treatment of silicon, we will focus on two main domains where these properties play a major role: cleaving techniques used to obtain a thin silicon layer for photovoltaic applications and MEMS. The evolution and validation of these new processes often rely on numerical simulations. The accuracy of these simulations, however, requires accurate input data for a wide temperature range. Numerous studies have been performed, and most of the needed parameters are generally available in the literature, but unfortunately, some discrepancies are observed in terms of measured data regarding fracture mechanics parameters. The aim of this article is to gather all these data and discuss the validity of these properties between room temperature and 1273 K. Particular attention is given to silicon fracture properties depending on crystallographic orientations, and to the brittle–ductile temperature transition which can strongly affect the quality of silicon layers.     

Deconfinement leads to changes in the nanoscale plasticity of silicon

Silicon crystals have an important role in the electronics industry, and silicon nanoparticles have applications in areas such as nanoelectromechanical systems, photonics and biotechnology. However, the elastic-plastic transition observed in silicon is not fully understood; in particular, it is not known if the plasticity of silicon is determined by dislocations or by transformations between phases. Here, based on compression experiments and molecular dynamics simulations, we show that the mechanical properties of bulk silicon and silicon nanoparticles are significantly different. We find that bulk silicon exists in a state of relative constraint, with its plasticity dominated by phase transformations, whereas silicon nanoparticles are less constrained and display dislocation-driven plasticity. This transition, which we call deconfinement, can also explain the absence of phase transformations in deformed silicon nanowedges. Furthermore, the phenomenon is in agreement with effects observed in shape-memory alloy nanopillars, and provides insight into the origin of incipient plasticity.     

光敏元件与光传感器的市场动态和发展

介绍了光敏元件与光传感器技术的发展及在国民经济和军事领域中的重要怍用；分析了国内外光电子产业的市场动态与发展趋势；论述了我国光电子产业面临的机遇和挑战。