Dissertations / Theses on the topic 'Β-FeSi2'

L'incertitude de l'énergie mondiale avec l'augmentation constante de la demande d'énergie déclenche la recherche de technologies de conversion d'énergie à haut rendement. Les dispositifs thermoélectriques (TE) peuvent jouer un rôle très important dans la collecte et la valorisation de l'énergie car ils peuvent être employés pour récupérer la chaleur résiduelle. Par exemple, la quantité de chaleur émise sous forme de déchets par les différents moteurs thermiques est évaluée en centaines de millions de MWh /an.Cette thèse vise à démontrer la faisabilité de fabrication des systèmes de récupération de la chaleur issue des déchets à l'échelle industrielle en utilisant des générateurs thermoélectriques (TE). Les techniques de fabrication proposées sont basées sur l'utilisation de technologies avancées comme le frittage par spark plasma, le broyage, la fusion laser sélective et la technologie de projection thermique. Ces techniques rendent possible l'élaboration de revêtements de matériau thermoélectrique avec des performances thermoélectriques supérieures et une flexibilité forte liées aux choix multiples de tailles, de formes et de matériaux.Nous nous sommes intéressés à l'étude du matériau semi-conducteur ß-FeSi2 car il présente un coefficient de mérite fort dans une plage de température de 300-800oC qui est la température des gaz en sortie de moteur voiture.Les techniques de SLM (Selective Laser Melting), de broyage, de frittage et de frittage flash (SPS) ont été successivement utilisées pour aboutir à l'élaboration de l'alliage ¿-FeSi2. Les revêtements ont ensuite été obtenus par la technique de projection plasma sous basse pression.Concernant le revêtement formé à partir de l'alliage par procédé LPPS, la transformation de phase de la phase cubique -ferrosilicium et de la phase quadratique ¿-Fe2Si5 en phase orthorhombique ß-FeSi2 se produit en obéissant aux réactions péritectique et eutectique. Après recuit sous température et temps appropriés, les revêtements présentent une phase complète ß-FeSi2 sur le substrat céramique.En outre pour une application à grande échelle, il est nécessaire de déposer ce type de revêtement sur un substrat en acier inoxydable et il convient dans ce cas d'utiliser un masque approprié pour fabriquer le dispositif thermoélectrique
The uncertainty in the global energy with the constant increase in energy demand triggers the search for energyconversion technologies with high efficiency. The thermoeletrical devices (TE) can play a relevant role in thecollection and recovery of energy because they can be used to recover waste heat. For example, the amount of heatemitted as waste by different ombustion engines is evaluated hundreds of millions of MWh / year.This thesis aims to demonstrate the feasibility of anufacturing heat recovery systems from waste on an industrialscale using thermoelectric generators (TE). The proposed manufacturing techniques are based on the use ofadvanced technologies such as spark plasma sintering, crushing, selective laser melting and thermal spraytechnology. These techniques make possible the development of thermoelectric material coatings with superiorthermoelectric performance and high flexibility related to multiple choices of sizes, shapes and materials.The study of semiconductor ß-FeSi2 material was conducted in this goal because it has a strong merit coefficient(ZT) in the temperature range of 300-800°C which is the temperature of the output gas of the cars.Selective Laser Melting, sintering and spark plasma sintering (SPS) were successively used to lead to themanufacture of ¿-FeSi2 alloy. The coatings were then obtained by low pressure plasma spraying.Concerning the coating formed from the alloy, the phase transformation of the cubic phase ¿-ferro-silicon and thetetragonal phase ¿-Fe2Si5 in the orthorhombic phase ß-FeSi2 is produced by obeying the eritectic and eutecticreactions. After annealing under suitable temperature and time, the coatings sprayed on the ceramic bstratepresent a complete phase ß-FeSi2.In view of a large-scale application, it is necessary to spray this type of coating on a stainless steel substrate and inthis case to use a suitable mask for making the appropriate thermoelectric device

碩士
義守大學
電子工程學系碩士班
94
The light-emitting devices are all fabricated by using Ⅲ-Ⅴ compound materials at the present day. However, the lattice constants of Ⅲ-Ⅴcompound materials are different from Si material, therefore the light-emitting devices can not integrate with Si chips. Recently, light emission from Si has been showed to be possible when the Si in the from of a low-dimensional system or when selected active impurities (such as erbium) and/or new phases (such as β-FeSi2). So far the studies of β-FeSi2 by many scholars have been focused on the investigation of its optical and electrical properties to find out the optimum thin film growth conditions. The theoretical investigation of β-FeSi2 light-emitting devices has not been reported. Thus, various laser diode structures (such as edge-emitting diode and surface-emitting diode) by using β-FeSi2 film as the action layer will be designed and analyzed in this proposal. First, the gain of β-FeSi2 /Si double heterostructure laser will be calculated. Then, the steady state solution of the rate equations will be solved to investigate the threshold characteristics and output power of β-FeSi2 /Si laser. The transient solutions of the rate equations will be calculated by using Analytic Solution to analyze the dynamic effects, frequency response and turn-on delay behavior of β-FeSi2 /Si laser, The analysis of rate equations can investigate the key factors that dominate the β-FeSi2/Si laser performances, These results can be used to fabricate the optimum β-FeSi2/Si laser structures.

碩士
國立成功大學
材料科學及工程學系碩博士班
101
In this study, self-catalyzed β-FeSi2 nanowires were synthesized via chemical vapor deposition method where the fabrication of β-FeSi2 nanowires occurred on Si(100) substrates through the decomposition of the single-source precursor of anhydrous FeCl3 powders. We carefully varied temperatures, duration time and the flow rates of carrier gases to control and investigate the growth of the nanowires. we can find that β-FeSi2 nanowires grow at about 750 ℃~ 850 ℃ and they are longer and thinner with increasing temperature . The number of nanowires was found fewer at higher gas flow rate, and the flow is less than 50sccm may have different phases appear. It is found that the longer duration time makes longer nanowires. β-FeSi2 in the PL IR spectra test can be found that there is a peak at 1380nm, it can be used as a light-emitting diode applications.The magnetism of β-FeSi2 nanowires is interesting as the result of various dimensions with different futures. β-FeSi2 bulk is non-magnetic,thin film ferromagnetic only below 100K, and in the magnetic analysis , there are room temperature ferromagnetic properties at the β-FeSi2 nanowires. In the field emission measurements, β-FeSi2 were good field emission materials.

碩士
國立交通大學
光電工程所
87
β-FeSi2 is an attractive material because of its high thermoelectric power，high absorption coefficient of visible light，and the integrating on silicon substrate﹒The thermal energy gap ofβ-FeSi2 has been reported 0.87eV－0.95eV in some literatures[1][2]﹒In this research，we synthesized and annealed theβ-FeSi2 in some different conditions﹒Theβ-FeSi2 was observed higher thermoelectric power in the condition that the syntheticβ-FeSi2 was quenched，and then annealed at 800℃，sustained 1000 hours﹒We also found that the copper-dopedβ-FeSi2 performed higher thermoelectric power﹒The higher thermoelectric power could be becauseβ-FeSi2 was formed fast fromε－FeSi and α－Fe2Si5 after annealing or doping copper﹒Structural characterizations were made by X-ray diffraction，Raman scattering，scanning electron microscopy and electron probe microanalyzer﹒Further more，ther result of measurement of resistivity as a function of reciprocal temperature is shown with a thermal energy gap 0.82eV－0.88eV﹒At low temperature(100K－200K)，the temperature dependence of the resistivity matched well with Mott''s exp(To/T)^(1/4)law，indicating high impurity and defect in our materials﹒

碩士
國立清華大學
材料科學工程學系
99
Transition metal silicide nanowires compose a highly broad set of refractory materials that are promising materials that are currently used for many applications including CMOS devices, thin film coatings, bulk structural components, electrical heating elements, photovoltaics, thermoelectric and spintronics. Semiconducting silicides have been extensively investigated for silicon-based optoelectronics such as LEDs and IR detectors. The narrow bandgap semiconducting silicides, in particular CrSi2, β-FeSi2, MnSi1.8, and ReSi1.75, have been targeted and used for robust, stable, and inexpensive thermoelectric materials, and have shown potential for photovoltaic applications. β-FeSi2 is a silicon-rich phase with a orthorhombic structure (space group Cmca) that has direct-bandgap . It allows for making light-emitting devices which operate at 1.5mm that incorporate β-FeSi2 into a conventional silicon bipolar junction. ε-FeSi is a metallic material with a cubic structure (space group P213) that has been classified as a Kondo insulator. It has attracted interest for over half a century, mainly because of its unusual magnetic behavior. β-FeSi2 and ε-FeSi nanowires were produced on silicon substrates covered with a thick layer of silicon oxide through the decomposition of the double-source precursor FeCl3 and SiO in a Oxygen Assisted Growth (OAG) process. Unlike typical Vapor-Liquid-Solid (VLS) NWs growth, The NWs form without the addition of metal catalysts had no catalyst tips. The morphologies and structure of NWs were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM shows that the diameter of the NWs is below 100nm and the length of NWs is tens of micrometers. XRD reveals that samples can grow in single phase or in double phase NWs depending on the growth temperature. Energy spectroscopy for chemical analysis (ESCA) shows the NWs are covered a thick SiO2 layer. TEM results indicate that the NWs growth is along the low index plane. We also have fabricated two-terminal electrical devices of β-FeSi2 and ε-FeSi NWs, and they exhibited average resistivity about 2000μΩ．cm and 250μΩ．cm. We found that the resistivity decreases stepwise as the NWs is thinned in semiconducting nanowires. In conclusion, we have successfully synthesized freestanding single-crystalline nanowires of β-FeSi2 and ε-FeSi by OAG method. This shows that semiconducting and metallic NWs will prove to be promising materials in future nanotechnology.

碩士
義守大學
電子工程學系
101
In this thesis,the responsivity characteristics of the p-n heterojunction photodiodes are investigated by using Si andβ-FeSi2 materials with different combinations of doping concentration and device thickness. In recent research report, the absorption coefficient and the wavelength range of absorption ofβ-FeSi2 material are larger than that of Si material. Therefore, the spectral responsivities of β-FeSi2 p-n heterojunction photodiode are also larger than that of Si photodiode. In this thesis, the drift and diffusion currents of photodiodes are calculated by solring the charge transport equations. Then the I-V characteristic curves and the responsivities of the photodiodes and obtained by these currents. The calculated results show that theβ-FeSi2 heterojunction photodiode has a good rectifying character and a good response to the NIR light. Theβ-FeSi2 / 4H-SiC photodiode with the doping concentration of 1015 cm-3 in p type β-FeSi2 absorption layer and the absorption layer thickness of 2.0 μm has a peak responsivity value of 398 mA / W at 1.189μm. Therefore, the is applicable to NIR optically-activated SiC based power switching devices.

碩士
義守大學
電子工程學系碩士班
97
The light-emitting devices are all fabricated by using Ⅲ-Ⅴ compound materials at the present day. However, the lattice constants of Ⅲ-Ⅴcompound materials are different from Si material, therefore the light-emitting devices can not integrate with Si chips. Recently, light emission from Si has been showed to be possible when the Si in the from of a low-dimensional system or when selected active impurities (such as erbium) and/or new phases (such as β-FeSi2). So far the studies of β-FeSi2 by many scholars have been focused on the investigation of its optical and electrical properties to find out the optimum thin film growth conditions. The theoretical investigation of β-FeSi2 light-emitting devices has not been reported. Thus, various laser diode structures (such as edge-emitting diode and surface-emitting diode) by using β-FeSi2 film as the action layer will be designed and analyzed in this proposal. First, the gain of β-FeSi2 /Si double heterostructure LED will be calculated. Then, the steady state solution of the rate equations will be solved to investigate the threshold characteristics and output power of β-FeSi2 /Si LED. The transient solutions of the rate equations will be calculated by using Analytic Solution to analyze the dynamic effects, frequency response and turn-on delay behavior of β-FeSi2 /Si LED, The analysis of rate equations can investigate the key factors that dominate the β-FeSi2/Si LED performances, These results can be used to fabricate the optimum β-FeSi2/Si LED structures.

碩士
義守大學
電子工程學系碩士班
96
β-FeSi2 is a Si-based semiconductor with a direct band gap of ∼0.83-0.87eV at room temperature. This feature makes the β-FeSi2 a potential candidate for the use in the light emitters. In this paper, the band structures of β-FeSi2 is calculated by tight-binding method(TBM). The results show that the direct and indirect band gaps of β-FeSi2 differ only 0.022eV. The other different band-structure calculating methods also show that the β-FeSi2 has the direct and indirect band gaps characteristics. Thus, the TBM can still be used to calculate the band structures of a complicated crystal such as β-FeSi2. And the physical characteristics of the band structures of β-FeSi2 are analyzed easierly by using TBM than the other methods.

碩士
義守大學
電子工程學系碩士班
98
The light-emitting devices are all fabricated by using Ⅲ-Ⅴ compound materials at the present day. However, the lattice constants of Ⅲ-Ⅴcompound materials are different from Si material, therefore the light-emitting devices can not be integrated with Si chips. Recently, light emission from Si has been showed to be possible when the Si in the form of a low-dimensional system or when selected active impurities (such as erbium) and/or new phases (such as β-FeSi2). So far the studies of β-FeSi2 by many scholars have been focused on the investigation of its optical and electrical properties to find out the optimum thin film growth conditions. The theoretical investigation of β-FeSi2 light-emitting devices has not been reported. Hence, in this study will design and analysis the DC characteristics and ideal internal quantum efficience of a double-heterostructure junction light-emitting diode fabricated by β-FeSi2 as designed and analyzed. By using semiconductor theory, the electric field, potential, band structure and carrier concentration distribution are calculated. To analyze DC characristic, By using theory of thermionic emission, the injection electron current density and leakage electron current density are calculated, then the rate equation will help us to obtain ideal internal quantum efficient. Analytical solutions will help us to know the effect of β-FeSi2-based LED lighting efficiency to accomplish highly internal efficiency light-emitting diode.

碩士
義守大學
電子工程學系
106
In this paper the responsivities and quantum efficiencies of p-Si/i-β-FeSi2/n-Si double heterostructure photodiodes and p-Si/i-Si/n-Si photodiodes are investigated by using self-developed analytical methods. The dark current densities of β-FeSi2 and Si p-i-n photodiodes under reverse-bias condition are calculated by solving the diffusion current densities of minority carriers. The photocurrent densities of β-FeSi2 p-i-n photodiode under illumination with reverse-bias are calculated by solving the drift current densities in the depletion regions. When the β-FeSi2 p-i-n photodiode incident wavelength < 0.6um, the magnitudes of responsivities and quantum efficiencies are almost zero for different intrinsic thicknesses. The maximum responsivity, R=0.65 A/W, and quantum efficiency, =65%, are both at =1.2um and the intrinsic β-FeSi2 layer thickness is 100um.The calculated responsivity of Si p-i-n photodiode is consistent with the reported researches. Therefore, the analysis methods are valid in this work. These results indicate the high application potential of β-FeSi2 as near-infrared photodiodes integrated with Si.

A metal-oxide-silicon (MOS) tunneling diode is utilized to embed beta-FeSi 2 precipitates and give strong 1.5 tam electroluminescence at 80 K. And this simple MOS structure with beta-FeSi2 was fabricated by Fe ion implantation and rapid thermal oxidation (RTO) at 900°C, which is fully compatible with ultra-large scale integration (ULSI) processes.
beta-FeSi2 precipitates are also incorporated into a silicon-on-insulator (SOI) rib waveguide and a p+-i-n+ photodetector is monolithically integrated with this SOI rib waveguide. The photoresponse to 1550 nm laser of beta-FeSi2 precipitates was observed and compared to intrinsic silicon.
Beta-phase iron disilicide (beta-FeSi2) is a semiconductor that can act as a light emitting material at the wavelength of 1.55 mum and can also be grown epitaxially on Si substrates. In this thesis, Fe ion implantation into silicon using a metal vapor vacuum arc (MEVVA) ion source was performed to synthesize nano-scale beta-FeSi2 precipitates in silicon matrix. The implantation was performed at ∼-120°C and the effects of silicon substrate and conditions for the following thermal annealing on luminescence properties were studied. The samples were characterized by employing various analytical techniques including Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), atomic force microscope (AFM), photoluminescence (PL), and electroluminescence (EL).
It is found that the PL intensity is optimized in p-100 silicon substrates (with the resistivity of 15-25 O·cm) using Fe ion implantation at a voltage of 80 kV and dosage of 5x1015 cm -2. Formation of beta-FeSi2 can be completed after rapid thermal annealing (RTA) and strong photoluminescence is present. We also found that RTA could maintain the strain in beta-FeSi2 precipitates and there exists an epitaxial relationship between beta-FeSi2 and silicon. Additional furnace annealing at 850°C can relax the strain in beta-FeSi2 precipitates.
The development of both modern microelectronics and lightwave technologies has enabled the establishment of the Internet which has introduced a profound change in our everyday lives. Because of Moore's law, computing today is limited less by the computation ability of microprocessors than by the rate at which the processor can communicate with the outside world. Lightwave technology has had many successes in the long-haul communication field over the past decade. The advantages of lightwave technology over conventional electronics are becoming apparent for shorter and shorter reach applications and lightwave communications may eventually replace copper-based interconnects in microelectronics. To make possible optical interconnects, optical components, especially light emitters may be needed to be integrated on conventional silicon microchips. However, to date, no efficient on-chip silicon-based light emitter is fabricated in silicon photonics.
Sun, Caiming.
Adviser: Hon K. Tsang.
Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3703.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2008.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstracts in English and Chinese.
School code: 1307.