晶体硅铸锭用氮化硅涂层失效机理及改性研究

氮化硅涂层是多晶硅铸锭必不可少的脱模剂,新型高效多晶硅铸锭对氮化硅涂层提出更高的要求。重点研究了氮化硅涂层在新型高效多晶硅铸锭过程中的失效机理,结果显示,氮化硅的碳化是导致氮化硅涂层与硅熔体间非浸润性降低,以及氮化硅涂层失效的主要原因。采用改进的溶胶-凝胶法（Sol-Gel）结合表面无碳处理制备增强型氮化硅涂层,该涂层在铸锭实验中显示出较高的强度及与硅熔体间良好的非浸润性,能够很好地满足新型高效多晶硅对氮化硅涂层的要求。     

Microstructure characteristics of silicon carbide coatings fabricated on C/C composites by plasma spraying technology

A functional gradient SiC coating on C/C composites has been developed using a novel process which is the combination of plasma spraying technology with reaction-formed heat-treatment. Microstructure observation and phase identification of the SiC coatings were analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Experimental results showed that a uniform silicon coating was deposited on C/C composite by plasma spraying technology. The reaction between the silicon coating and C/C substrate occurred during the heat-treatment at temperature of 1450 °C and 1600 °C in argon environment, respectively. A continuous SiC coating was formed on the surface of the C/C substrate. And a layer of SiC/C convention layer was formed on the near-surface area of the substrate, which was resulted from the molten silicon penetrating into the open pores and consequently reacting with the C/C composites. The thickness of the formed SiC coatings was closely related to the original silicon coatings.     

Chemical stability of silicon nitride coatings used in the crystallization of photovoltaic silicon ingots. Part I: Stability in vacuum

Photovoltaic silicon is currently grown in silica crucibles coated with an oxidized silicon nitride powder, which acts as an interface releasing agent between the silicon and the crucible. A series of experiments was performed to study the reactions between coating components under high vacuum, varying the temperature, the holding time and the oxygen content in the coating. The results are discussed with the help of a simple analytical model taking into account the diffusive transport of reaction species from the inside of the porous coating to its surface and then their evaporation into the vapour phase.     

Detonation synthesis of nanoscale silicon carbide from elemental silicon

Direct reaction of precursors with the products of detonation remains an underexplored area in the ever-growing body of detonation synthesis literature. This study demonstrated the synthesis of silicon carbide during detonation by reaction of elemental silicon with carbon products formed from detonation of RDX/TNT mixtures. Continuum scale simulation of the detonation showed that energy transfer by the detonation wave was completed within 2–9 μs depending on location of measurement within the detonating explosive charge. The simulated environment in the detonation product flow beyond the Chapman-Jouguet condition where pressure approaches 27 GPa and temperatures reach 3300 K was thermodynamically suitable for cubic silicon carbide formation. Carbon and added elemental silicon in the detonation products remained chemically reactive up to 500 ns after the detonation wave passage, which indicated that the carbon-containing products of detonation could participate in silicon carbide synthesis provided sufficient carbon-silicon interaction. Controlled detonation of an RDX/TNT charge loaded with 3.2 wt% elemental silicon conducted in argon environment lead to formation of ～3.1 wt% β-SiC in the condensed detonation products. Other condensed detonation products included primarily amorphous silica and carbon in addition to residual silicon. These results show that the energized detonation products of conventional high explosives can be used as precursors in detonation synthesis of ceramic nanomaterials.     

Electrochemical characteristics of amophous carbon coated silicon electrodes

The properties of carbon films deposited by the radio frequency plasma sputtering of a fullerene C₆₀ target were investigated to elucidate the dependence on the plasma power. A radio frequency argon plasma power ranging from 50 to 300W at a pressure of 1.3 Pa was applied for sputtering. This corresponds to a self-bias potential on the target ranging from −95 to −250 V and a maximum argon ion energy ranging from 240 to 575 eV. The analysis of the G and D peaks in the Raman spectra shows that the films are similar to tetragonal hydrogenated amorphous carbon annealed at 600–1,000 °C. The electron band structure of the carbon films deposited by the sputtering of C₆₀ depends on the plasma power. The coating effect of these carbon films on the capacity performance of the silicon film electrode of lithium secondary batteries was significant in our experimental range. An electrochemical test revealed that such carbon thin film on the silicon electrode plays an important role in mitigating the capacity fading during the charge and discharge processes. The test revealed that the film formed at a plasma power of 300 W is the most effective.     

直拉法单晶硅制备过程控氧技术研究进展

随着我国光伏行业的快速发展,直拉(CZ)法制备的单晶硅朝着大尺寸、高品质、低成本的方向发展,然而随着单晶硅尺寸越来越大,其内部氧杂质含量偏高的问题也越来越突出。本文在介绍CZ法制备单晶硅过程中氧杂质传输机理的基础上,归纳总结了单晶硅生产过程的控氧技术现状,分析了热场结构优化、工艺优化、掺杂元素、氩气流场优化以及新型CZ技术对单晶硅氧杂质含量的影响规律,并对控氧技术的发展方向提出了展望。     

Making reusable reaction-bonded silicon nitride crucibles for silicon casting from kerf-loss silicon waste

Silicon kerf loss during wafer slicing and the broken quartz crucibles after silicon casting are two major solid wastes from photovoltaic (PV) industry. Especially, the recycle of kerf-loss silicon has become an urgent issue because near 100 000 t of solid wastes are generated every year. One of the most meaningful recycle routes of the kerf-loss silicon is to make silicon nitride crucibles to replace the quartz crucibles. In this study, we demonstrated how this is feasible through acid leaching refining, slip casting, and nitridation. The reaction-bonded silicon nitride (RBSN) crucibles after oxidation were found pure enough for silicon ingot growth. More importantly, they could be reused after ingot growth. With the present examples, the potential of using the kerf-loss silicon for fine ceramics is prominent.     

An improved electrochemical cell for the characterization of silicon/electrolyte interfaces

An electrochemical cell was made of a Teflon tube which was tightly pressed on the surface of a silicon wafer. The Teflon/silicon contact was tight enough to prevent any infiltration of solution, because it was observed that confined electrolyte was a source of irreproducibility. The device was enclosed within a black polyvinyl box which protected the sample against room light but allowed irradiation with a controlled light intensity. The cell was fed under argon pressure with a thoroughly degassed electrolyte, and the whole volume inside was maintained under argon atmosphere. This cell permitted very stable and reliable rest potential measurement and current–potential diagrams. The method proved useful in the study of the influence of light irradiation and of dissolved oxygen or metal ions trace impurities in the electrolyte.     

Synthesis and characterization of mesoporous silicon carbide

A modified sol–gel method is proposed for the preparation of mesoporous silicon carbide. In this method, tetraethoxysilane (TEOS) and phenolic resin are used for preparing a binary carbonaceous silicon xerogel, and nickel nitrate is employed in the sol–gel process as a pore-adjusting reagent. SiC was produced in the carbothermal reduction of the binary xerogel at 1250 °C in an argon flow (40 cm³ min⁻¹) and purified by removing excess silica, carbon and other impurities. The purified SiC sample was characterized by XRD, SEM, TEM, and N₂ adsorption, and the results showed that the SiC sample had a surface area of 112 m² g⁻¹ (BET) and an average pore diameter of about 10 nm.     

The microstructure of polymer-derived amorphous silicon carbide layers

In order to achieve thin amorphous silicon carbide layers a two-stage process was applied. The deposition of thin layers from liquid chlorovinylsilanes was carried out under argon flow using a spin-coating-system. Afterwards, the samples were pyrolysed in a temperature range between 800 °C and 1200 °C with different hydrogen concentrations in the atmosphere. Additionally, bulk material was pyrolysed in order to characterise structural changes by transition oligomer to a-SiC:H.In this work we present studies on the structure of the layers and of bulk material, which were carried out by XRD, MAS NMR and Raman spectroscopy, depending on pyrolysis conditions. Following results were obtained: Both, silicon carbide layers and bulk material, pyrolysed at 800 °C, were amorphous. Increase of the temperature to 1200 °C leads to a partial amorphous-to-crystalline transition forming β-SiC. Moreover, derivations from stoichiometric SiC were observed: Free silicon was found in thin layers, whereas crystallites of graphite were detected in the bulk material. The amount of excess carbon can be influenced by addition of hydrogen to the pyrolysis atmosphere.     

Novel synthesis and characterization of silicon carbide nanowires on graphite flakes

Silicon carbide nanowires were synthesized on the surface of graphite by partially reacting with silicon powders in NaF–NaCl based salt at 1150–1400 °C in argon. The effects of temperature and time of heat treatment as well as Si/graphite ratio on synthesis of SiC nanowires were studied. The results showed that the formation of SiC nanowires started at about 1200 °C, and the amounts of SiC nanowires increased in the resultant powders with increasing temperature. Their morphologies were characterized by scanning electron microscopy and high-resolution transmission electron microscopy. It was found that β-SiC nanowires with diameter of 10–50 nm and various lengths grew along their preferred direction perpendicular to (111). The zeta potential of graphite was also increased after coating with silicon carbide nanowires. SiC nanowires that formed on the graphite surface acted as an anti-oxidant to a certain extent, and they protected the inner graphite from oxidation.     

Weibull strength size effect of diamond wire sawn photovoltaic silicon wafers

A good comprehension of the mechanical properties of photovoltaic silicon wafers is crucial to maintain low breakage rates during solar cell manufacturing. As brittle material, silicon wafers are theoretically subject to a strength size effect. This study aims at determining whether this effect should be considered when comparing the strength of photovoltaic wafers. We derive a theoretical strength scaling law and perform an extensive experimental study on 240 diamond-wire sawn silicon wafers, which have the particularity of exhibiting an anisotropy in Weibull parameters. We compare test results from three different bending configurations and show that a size effect is only observable when loading the wafers perpendicular to the saw marks. Strength values obtained when loading the wafers in the direction of the wire yield identical results regardless of the size of the tested area. These findings can open up prospects for the standardization of testing methods for photovoltaic wafers.     

无取向硅钢用磷酸盐涂层材料 制备及其防腐性能

系统研究了无取向硅钢用磷酸盐系涂层性能的影响因素。以氢氧化铝和磷酸为原料制备磷酸二氢铝,再添加适量的添加剂酒石酸铵、二氧化硅、环氧树脂,得到的涂液涂布于硅钢表面,并控制合适的烘干温度,通过耐盐雾实验考察各因素对涂液耐腐蚀性能的影响。实验结果表明,在磷酸与氢氧化铝物质的量比为3.4∶1、酒石酸铵用量为2%、二氧化硅用量为1%、环氧树脂用量为5%、烘干温度为300 ℃条件下,所得涂层材料的防（耐）腐蚀效果最佳。     

Effect of the etching time on the morphological, optical and electronic properties of silicon nanowires

ABSTRACT: Owing to their interesting electronic, mechanical, optical and transport properties, silicon nanowires (SiNWs) have attracted much attention, giving opportunities to several potential applications in nanoscale electronic, optoelectronic devices and silicon solar cells. For photovoltaic (PV) application, a superficial film of SiNWs could be used as an efficient antireflection coating (ARC). In this work, we investigate the morphological, optical and electronic properties of SiNWs fabricated at different etching time. Characterizations of the formed SiNWs films were performed using a Scanning Electron Microscope (SEM), UV-Vis-NIR spectrophotometer and Light-Beam-Induced-Current (LBIC) technique. The later technique was used to determine the effective diffusion length in SiNWs films. From LBIC investigations, we deduce that the homogeneity of the SiNWs film play a key role on the electronic properties.     

Current improvement of porous silicon photovoltaic devices by using double layer porous silicon structure: applicable in porous silicon solar cells

The photoluminescence (PL) phenomena of porous silicon (PS) samples with different etching times were examined to find out a relationship between PL emission energy (experimental value of PS band gap energy) and the etching time for fabrication of double (two) layer porous silicon sample on one silicon substrate. The dependence of PL Peak energy with etching time was discussed. A double layer PS structure was formed by using two electrochemical reactions with different etching times of 20 and 10 min, respectively. The photovoltaic (PV) properties of mono layer and double layer porous silicon PV devices were examined and compared. The main result is the enhanced short-circuit current (I_sc) of double layer PS structure compared to monolayer ones.     

Synthesis and characterization of submicron silicon carbide powders with silicon and phenolic resin

A novel three-step process is used to fabricate submicron silicon carbide powders in this paper. The commercially available silicon powders and phenolic resin are used as raw materials. In the first step, precursor powders are produced by coating each silicon powder with phenolic resin shell. Then, precursor powders are converted into carbonized powders by decomposing the phenolic resin shell. The submicron silicon carbide powders are formed in the reaction of silicon with carbon during the third step of thermal treatment. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric (TG) analyses are employed to characterize the microstructure, phase composition and free carbon content. It is found that the sintered powders consist of β-SiC with less than 0.2 wt.% of free carbon. The particle size of the obtained silicon carbide powders varies from 0.1 to 0.4 μm and the mean particle size is 0.2 μm. The silicon carbide formation mechanism of this method is based on the liquid-solid reaction between liquid silicon and carbon derived from phenolic resin. The heat generated during the reaction leads to great thermal stress in silicon carbide shell, which plays an important role in its fragmenting into submicron powders.     

Processing and properties of plasma sprayed silicon nitride-glass composite coatings

Abstract

Abstract

Silicon nitride decomposes before it can melt, and so thermal spraying of pure silicon nitride powder is impracticable. To address this difficulty, feedstock powder for plasma spray deposition has been developed in which each particle is a composite of silicon nitride in a low temperature borosilicate glass matrix. The research showed that the silicon nitride did not decompose in the plasma because the low thermal conductivity of the glass matrix ensured a low heat transfer rate and the particle temperature remaining below the decomposition temperature. The coating density initially increased with plasma arc power because of increasing splat flow but then declined at high power levels owing to decomposition of the glass matrix. The silicon nitride dispersion substantially reduced the splat flow, particularly near the maximum packing fraction, but also had the beneficial effect of restricting crack propagation, resulting in an optimum content for wear resistance of 30?vol.-% silicon nitride.     

Phosphorus diffusion gettering process of multicrystalline silicon using a sacrificial porous silicon layer

ABSTRACT: The aim of this work is to getter undesirable impurities from low cost multicrystalline silicon (mc-Si) wafers and then enhance their electronic properties. We used an efficient process which consists in applying phosphorus diffusion into a sacrificial porous silicon (PS) layer in which the gettered impurities have been trapped after the heat treatment. As we have expected, after removing the phosphorus-rich porous silicon (PS) layer, the electrical properties of the mc-Si wafers were significantly improved. The PS layers, realized on both sides of the mc-Si substrates, were formed by the stain-etching technique. The phosphorus treatment was achieved using a liquid POCl3-based source on both sides of the mc-Si wafers. The realized phosphorus/PS/Si/PS/phosphorus structures were annealed at a temperature ranging between 700 degreesC and 950 degreesC under an O2 controlled atmosphere, which allows phosphorus to diffuse throughout the PS layers and to getter eventual metal impurities towards the phosphorus doped PS layer. The effect of this gettering procedure was investigated by means of the internal quantum efficiency (IQE) and the dark current-voltage (I-V) characteristics. The minority carrier lifetime measurements were made using a WTC-120 photoconductance lifetime tester. The serial resistance and the shunt resistance carried out from the dark (I-V) curves confirm this gettering-related solar cell improvement. It has been shown that the photovoltaic parameters of the gettered silicon solar cells were improved as regard to the ungettered one, what proves the beneficial effect of this gettering process on the conversion efficiency of the multicrystalline silicon solar cells.     

硅钢级氧化镁的研究进展

随着中国电工钢产量的增加,硅钢级氧化镁需求量不断增加,传统的以白云石为原料制备氧化镁的工艺已经无法满足市场需求。中国是一个卤水资源丰富的国家,因此,研究如何资源化综合利用盐湖资源变得越来越重要。硅钢级氧化镁是一种制备取向硅钢的涂层材料,主要用于取向硅钢高温退火处理阶段,起到隔离剂、绝缘膜层、脱硫、脱磷等作用。综述了制备硅钢级氧化镁的方法、工艺流程、研究进展及存在的问题,指出了硅钢级氧化镁制备技术的发展方向,并对中国卤水资源的利用提出了建议。     

Influence of the silicon and oxygen content on the properties of non-hydrogenated amorphous carbon coatings

This work reports the development of non-hydrogenated magnetron-sputtered silicon and silicon-oxygen containing amorphous carbon coatings with increasing silicon and oxygen contents respectively. The Si content of a-C:Si coatings increases linearly with the increase of the power applied to the Si target up to 24 at.%, while to the system a-C:Si:O the O content increases with the increase of the oxygen flow to a maximum of 27 at.%. The hardness of the a-C:Si coatings shows two distinct trends with the increase of the Si content, a decrease of hardness for Si contents lower than 10 at.% and an increment above this value are observed. The coatings of the system a-C:Si:O present a decrease of hardness and Young modulus with the increase of the O content. The tribological performance of the coatings is significantly improved by doping the amorphous carbon coatings with silicon and oxygen with a reduction of the friction from 0.17 for the undoped carbon coating to 0.034 for the coating of the system a-C:Si:O with the highest O content.