Tesi: "Metal-Assisted chemical etching of silicon"

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MAGAGNA, STEFANO. "Thermoelectric nanostructured silicon obtained by Metal-assisted Chemical Etching". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/312087.

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Abstract (sommario):

Il mio progetto di tesi prevede la preparazione di materiali a base di nanofili di silicio, sfruttando una via sintetica in soluzione: il Metal-assisted Chemical Etching (MaCE). La tecnica prevede l’immersione del substrato monoscristallino <100> di Silicio in una soluzione di acido fluoridrico, contenente una sorgente di ioni Ag+ (AgNO3). Il processo consiste sostanzialmente nell’ossidazione localizzata del Silicio, catalizzata dagli ioni Ag+; l’ossido di Silicio così formato viene successivamente disciolto dal HF presente in soluzione, permettendo la formazione di nanofili per etching chimico. Nonostante il MaCE sia una tecnica diffusamente utilizzata a livello sperimentale, l’effettivo meccanismo del processo è ancora fortemente dibattuto in letteratura. Grazie al mio periodo a Marsiglia, ho potuto caratterizzare a fondo dal punto di vista morfologico i vari nanofili ottenuti da substrati a diverse concentrazioni di drogante, diverse specie droganti. E’ stata, inoltre, variata sistematicamente la temperatura di attacco, nonché la concentrazione di Ag+ all’interno della soluzione. I risultati ottenuti grazie ad una avanzata analisi morfologica con SEM (Scanning Electron Microscopy) e TEM (Transmission Electron Microscopy) hanno permesso di aprire una riflessione e avanzare teoria su diversi aspetti dell’etching, dal trasferimento elettronico alla localizzazione dell’attacco. La versatilità del MaCE permette la sintesi di un metamateriale, introdotto nel 2014 da Davis et al, costituito da una membrana di Silicio sulla quale è posto un array di nanofili di Silicio e definito “Nanophononic Metamaterial (NPM)”. L’interazione tra i modi fononici introdotti dai nanofili all’interno del film e i modi del film stesso porterebbe il NPM ad una conducibilità termica del 48%, rispetto a quella del corrispettivo film sottile senza nanopillars, grazie una ibridizzazione delle curve di dispersione fononica e la comparsa di modi fononici piatti e localmente risonanti. Inoltre, visto che il trasporto elettronico avviene nella membrana che rimane priva di difetti o inclusioni, le proprietà elettroniche del NPM risultano conservate, rendendolo ideale per applicazioni termoelettriche vista la bassa conducibilità termica risultante. NPM con diversi spessori di membrana sono stati prodotti partendo da un wafer Double-Side-Polished di 200 micron di spessore, sul quale sono stati prodotti i nanofili tramite MaCE, su entrambe le facce. Scegliendo la lunghezza dei nanofili è stato possibile regolare lo spessore della membrana residua. Le caratterizzazioni elettriche e termoelettriche hanno dimostrato come il comparto elettronico del NPM sia mantenuto. La caratterizzazione termica di una membrana con spessore di 62 micron ha ottenuto una conducibilità termica pari al 36% di quella del Silicio bulk. Questo materiale, quindi, permette di disaccoppiare la conducibilità elettrica (regolata dalle caratteristiche della membrana) dalla conducibilità termica (controllata dalla presenza dei nanofili), rendendolo ideale per applicazioni termoelettriche.
The necessity of sustainability in energy production and the continuous increasing of global warming, which leads to tremendous consequences, are among the most complicated challenges facedby humanity along its history. Reduction of the energy wastes anda strong energetic efficiency improvement are the most relevant solutions proposed, since nearly the 60 % of the energy generated around the world is wasted as heat. The possibility to recover even a small amount of this wasted energy could lead to a significant decrease of CO2 emission. Thermoelectric devices can actively contribute to this cause sincethey allow to generate electrical power even with small temperature gradients and without moving parts. Their efficiency is described by the figure of merit zT. Therefore, an ideal thermoelectric material should have, at the same time,good electrical properties combined to a low thermal conductivity ,a difficult challenge considering that, normally, a good electrical conductor is also a good thermal conductor. However, property modification at nanoscale opened a new pathway in thermoelectric materials research. The work of this PhD thesis is focused on the nanostructuration of a non-toxic, earth-abundant material such as Silicon. Due to the high thermal conductivity, bulk silicon is not suitable for thermoelectric application. Anyway, nanostructuration offers efficient and innovative ways to lower silicon thermal conductivity and to open novel opportunities to its usage as thermoelectric material. In the first part, the mechanism of Silver-assisted Chemical etching (SaCE), a one-step method chosen for the production of silicon NW will be presented. Particularly, the results of anextended analysis of the interplay among doping level and type of silicon, nanowire morphology and the parameters controlling thechemistry of SaCE will be shown. SaCE occurs at the outer substrate surface as a result of Si extrusion by sinking self-propelled Ag particles which causes Si flakes to be exposed at the outer solution-substrate. Here, the etching actually occurs through either 2- or 4-electron electrochemical oxidation of Si. NW surface is found to be either porous (potholed) or crystalline depending on the predominant electrochemical process. The prevalence of either 2- or4-electron processes is controlled by the material resistivity andtherefore by the voltage sensed by silicon. Two-electron processes occur at low voltages for conductive, heavily doped Si,and causes the formation of superficially potholed NWs. Four-electron processes occur for weakly doped Si and lead to fully crystalline NWs.Secondly, the production, by means of SaCE, and the characterization of a recently introduced category of material, the so-called Nanophononic Metamaterial (NPM), will be presented. This material is composed by an array of silicon nanopillars on top of a silicon thin film. The hybridization of the locally-resonant phonon modes introduced by the NWs with membrane phonon modes leads to a thermal conductivity reduction. NPM demonstrates to retain electrical and thermal conductivity of the wafer from which it is etched. Preliminary thermal measurements showed a thermal conductivity reduction of 2/3 with respect of bulk silicon. In the third part, the characterization of heavily doped Si NWs arrays, produced by SaCE, will be presented. This kind of arrays shows very low thermal conductivity (around 2 W/ (m K)) and a Seebeck coefficient comparable with that of heavily doped bulk silicon. Anyway, due to the presence of the substrate (very thick if compared with NWs length), it is complicated to have a precise measurement of NW resistivity. To overcome this issue, a new structure exclusively made of NWs and free from any substrate contribution will be presented.

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Magagna, Stefano. "Thermoelectric nanostructured silicon obtained by metal-assisted chemical etching". Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0166.

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Mon projet de thèse implique la préparation de matériaux à base de nanofils de silicium, exploitant la solution de manière synthétique : gravure chimique assistée par métal (MaCE). J'ai pu pleinement caractériser depuis le point de vue morphologique des différents nanofils obtenus à partir de substrats à différentes concentrations de dopants, différentes espèces de dopants. La température d'attaque, ainsi que la concentration d'Ag + dans la solution. Les résultats autorisent à ouvrir une réflexion et une théorie avancée sur différents aspects de gravure, du transfert électronique de la localisation de l'attaque. MaCE permet la synthèse d'un métamatériau, introduit en 2014 par Davis et al, consistant à partir d'une membrane de silicium sur laquelle un réseau de nanofils de silicium et définition du "métamatériau nanophononique (NPM) ". NPM avec différentes épaisseurs de membrane ont été produites à partir d'une plaquette polie double face de 200 microns d'épaisseur, sur laquelle ils étaient produit les nanofils par MaCE, sur les deux faces. En choisissant la longueur des nanofils, il était possible d'ajuster l'épaisseur de la membrane résiduelle. Les caractérisations électriques et thermoélectriques ont montré comment le compartiment électronique du NPM est maintenu. La caractérisation thermique d'une membrane d'une épaisseur de 62 microns a obtenu une conductivité thermique égale à 36% de celui du silicium en vrac. Ce matériau nous permet donc de découpler la conductivité électrique (régulée par les caractéristiques de la membrane) de la conductivité thermique (contrôlée par la présence des nanofils), ce qui le rend idéal pour des applications thermoélectriques
My thesis project involves the preparation of materials based on silicon nanowires, synthetically exploiting solution: metal-assisted chemical etching (MaCE). I have been able to fully characterize sinc emorphological point of view the different nanowires obtained from substrates at different dopant concentrations, different dopant species. The temperature of attack, as well as the concentration of Ag + in the solution. The results allowed to open a reflection and an advanced theory on different aspects engraving, from electronic transfer to localization of the attack. MaCE allows the synthesis of ametamaterial, introduced in 2014 by Davis et al, consisting of from a silicon membrane on which a network of silicon nanowires and definition of "nanophononic metamaterial (NPM) ". NPM with different membrane thicknesses were produced from a 200 micron thick double-sided polished wafer, on which they were produced the nanowires by MaCE, on both sides. By choosing the length of the nanowires, it was possible to adjust the thickness of the residual membrane. Characterizations electric and thermoelectric have shown how the electronic compartment of the NPM is maintained. The thermal characterization of a membrane with a thickness of 62 micron has obtained a thermal conductivity equal to 36% of that of bulk silicon. This material therefore allows you to decouple the electrical conductivity (regulated bymembrane characteristics) thermal conductivity (controlled by the presence of nanowires), which makes it ideal for thermoelectric applications

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Ngqoloda, Siphelo. "Vertically aligned silicon nanowires synthesised by metal assisted chemical etching for photovoltaic applications". University of the Western Cape, 2015. http://hdl.handle.net/11394/4872.

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>Magister Scientiae - MSc
One-dimensional silicon nanowires (SiNWs) are promising building blocks for solar cells as they provide a controlled, vectorial transport route for photo-generated charge carriers in the device as well as providing anti-reflection for incoming light. Two major approaches are followed to synthesise SiNWs, namely the bottom-up approach during vapour-liquid-solid mechanism which employs chemical vapour deposition techniques. The other method is the top-down approach via metal assisted chemical etching (MaCE). MaCE provides a simple, inexpensive and repeatable process that yields radially and vertically aligned SiNWs in which the structure is easily controlled by changing the etching time or chemical concentrations. During MaCE synthesis, a crystalline silicon (c-Si) substrate covered with metal nanoparticles (catalyst) is etched in a diluted hydrofluoric acid solution containing oxidising agents. Since the first report on SiNWs synthesised via MaCE, various publications have described the growth during the MaCE process. However lingering questions around the role of the catalyst during formation, dispersion and the eventual diameter of the nanowires remain. In addition, very little information pertaining to the changes in crystallinity and atomic bonding properties of the nanowires post synthesis is known. As such, this study investigates the evolution of vertical SiNWs from deposited silver nanoparticles by means of in-depth electron microscopy analyses. Changes in crystallinity during synthesis of the nanowires are probed using x-ray diffraction (XRD) and transmission electron microscopy (TEM). Deviations in the optical properties are quantified using optical reflectivity measurements by employing ultraviolet-visible (UV-Vis) spectroscopy, whereas the bonding configurations of the nanowires are probed by Raman and Fourier transforms infrared spectroscopy. Diameters of 50 – 200 nm vertical SiNWs were obtained from scanning electron micrographs and nanowires lengths linearly increased with etching time duration from about 130 nm after 30 seconds to over 15 μm after 80 minutes. No diameter modulations along nanowires axial direction and rough nanowires apexes were observed for nanowires obtained at longer etching times. These SiNWs remained crystalline as their bulk single crystalline Si wafers but had a thin amorphous layer on the surface, findings confirmed by TEM, XRD and Raman analysis. Nanowires were found to be partially passivated with oxygen with small traces of hydrogen termination, confirmed with infrared absorption studies. Finally, low optical reflection of less than 10% over visible range compared to an average of 30% for bulk Si were measured depicting an antireflective ability required in silicon solar cells.

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Hildreth, Owen James. "Development of metal-assisted chemical etching as a 3D nanofabrication platform". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/49011.

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The considerable interest in nanomaterials and nanotechnology over the last decade is attributed to Industry's desire for lower cost, more sophisticated devices and the opportunity that nanotechnology presents for scientists to explore the fundamental properties of nature at near atomic levels. In pursuit of these goals, researchers around the world have worked to both perfect existing technologies and also develop new nano-fabrication methods; however, no technique exists that is capable of producing complex, 2D and 3D nano-sized features of arbitrary shape, with smooth walls, and at low cost. This in part is due to two important limitations of current nanofabrication methods. First, 3D geometry is difficult if not impossible to fabricate, often requiring multiple lithography steps that are both expensive and do not scale well to industrial level fabrication requirements. Second, as feature sizes shrink into the nano-domain, it becomes increasingly difficult to accurately maintain those features over large depths and heights. The ability to produce these structures affordably and with high precision is critically important to a number of existing and emerging technologies such as metamaterials, nano-fluidics, nano-imprint lithography, and more. Summary To overcome these limitations, this study developed a novel and efficient method to etch complex 2D and 3D geometry in silicon with controllable sub-micron to nano-sized features with aspect ratios in excess of 500:1. This study utilized Metal-assisted Chemical Etching (MaCE) of silicon in conjunction with shape-controlled catalysts to fabricate structures such as 3D cycloids, spirals, sloping channels, and out-of-plane rotational structures. This study focused on taking MaCE from a method to fabricate small pores and silicon nanowires using metal catalyst nanoparticles and discontinuous thin films, to a powerful etching technology that utilizes shaped catalysts to fabricate complex, 3D geometry using a single lithography/etch cycle. The effect of catalyst geometry, etchant composition, and external pinning structures was examined to establish how etching path can be controlled through catalyst shape. The ability to control the rotation angle for out-of-plane rotational structures was established to show a linear dependence on catalyst arm length and an inverse relationship with arm width. A plastic deformation model of these structures established a minimum pressure gradient across the catalyst of 0.4 - 0.6 MPa. To establish the cause of catalyst motion in MaCE, the pressure gradient data was combined with force-displacement curves and results from specialized EBL patterns to show that DVLO encompassed forces are the most likely cause of catalyst motion. Lastly, MaCE fabricated templates were combined with electroless deposition of Pd to demonstrate the bottom-up filling of MaCE with sub-20 nm feature resolution. These structures were also used to establish the relationship between rotation angle of spiraling star-shaped catalysts and their center core diameter. Summary In summary, a new method to fabricate 3D nanostructures by top-down etching and bottom-up filling was established along with control over etching path, rotation angle, and etch depth. Out-of-plane rotational catalysts were designed and a new model for catalyst motion proposed. This research is expected to further the advancement of MaCE as platform for 3D nanofabrication with potential applications in thru-silicon-vias, photonics, nano-imprint lithography, and more.

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Khanyile, Sfiso Zwelisha. "Silicon nanowires by metal-assisted chemical etching and its incorporation into hybrid solar cells". University of Western Cape, 2021. http://hdl.handle.net/11394/8340.

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Philosophiae Doctor - PhD
The rapid increase in global energy demand in recent decades coupled with the adverse environmental impact of conventional fuels has led to a high demand for alternative energy sources that are sustainable and efficient. Renewable solar energy technologies have received huge attention in recent decades with the aim of producing highly efficient, safe, flexible and robust solar cells to withstand harsh weather conditions. c-Si has been the material of choice in the development of conventional inorganic solar cells owing to it superior properties, abundance and higher efficiencies. However, the associated high costs of Si processing for solar cells have led to a gravitation towards alternative organic solar cells which are cheaper and easy to process even though they suffer from stability and durability challenges. In this work, combination of both inorganic and organic materials to form hybrid solar cells is one of the approaches adopted in order to address the challenges faced by solar cell development.

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Zheng, Wen Ph D. Massachusetts Institute of Technology. "Fabrication of capacitors based on silicon nanowire arrays generated by metal-assisted wet chemical etching". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104114.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 170-177).
Capacitors with high capacitance density (capacitance per footprint area) have potential applications in autonomous microsystems that harvest energy from the environment, as they can store and release energy at high rates. Use of high surface-to-volume ratio structures has been demonstrated as an effective way to increase the electrode area, and therefore to improve the capacitance density, while still keeping the footprint area low. The goal of this thesis was to first develop an understanding of the mechanisms of metal assisted wet chemical etching for fabrication of arrays of silicon nanowires, and then use this understanding to build nanowire array on-chip capacitors in silicon substrates, in order to eliminate additional packaging and enable local and efficient energy delivery. Two types of capacitors were investigated: electrostatic metal-oxide-semiconductor (MOS) capacitors for power management, and supercapacitors for energy storage purposes. For both types of devices, enlarged surface area per footprint was achieved by utilizing the arrays of silicon nanowires. Fundamental studies of the roles of metals in metal-assisted chemical etching (MACE) of silicon were conducted. Lithography techniques were used to generate patterns in metal films which when subjected to MACE resulted in formation of ordered arrays of silicon nanowires. Investigation of various metal catalysts showed that Pt is a more active catalyst than Au, while Cu is not stable in the etchant. Tapered silicon nanowires can be generated by adding a layer of Cu between two Au layers, and etching occurs much faster than when a pure Au catalyst is used. While carrying out research on the mechanisms of MACE, we developed a new electrochemical method for formation of arrays of silicon nanowires, metal-assisted anodic etching (MAAE). In this process, the etchant consists of HF alone, and does not include an oxidant. In both processes, HF is used as an etchant. However, in MACE, electronic holes are supplied through reduction of an oxidant (e.g. H₂O₂), while in MAAE, electronic holes are supplied through an external circuit, with anodic contact to either the metal or the silicon. In both contact cases for MAAE, the metal catalyzes the etching process and leads to controlled formation of silicon nanowires, without the need for an oxidant. This discovery, and its analysis, provided new insights into the mechanisms of both MAAE and MACE, and also opened the possibility for use of metal catalyzed electrochemical etching of other materials that cannot survive the HF/oxidant mixture. Processes for fabrication of on-chip capacitors based on silicon nanowires were next developed. We first fabricated on-chip MOS capacitors with nanowire arrays etched using MACE with both single crystal silicon substrates and polycrystalline silicon films. For wires made in both cases, the capacitance density followed a same scaling trend related to their geometries. Epitaxial wafers were used with a post-etch doping process to reduce the series resistance in the devices in order to obtain a better frequency response, as desired for high frequency circuits. To achieve higher capacitance densities for energy storage purposes, we also designed a solid state supercapacitor device based on nanowires etched using MAAE with heavily doped n-type silicon substrates. The silicon nanowires were coated with RuO₂ using atomic layer deposition (ALD) to achieve a high capacitance. In this case, charge is stored through the formation of an electrical double layer and through reversible redox reactions. We showed that the capacitance density of these devices roughly scaled with the increased surface area of silicon nanowire arrays. The solid state supercapacitor achieved a capacitance density of 6.5mF/cm², which is comparable to the best results achieved with other types of on-chip supercapacitors. In contrast with other processes for forming on-chip supercapacitors, the supercapacitors we demonstrated were fabricated using a fully complementary metal-oxide-semiconductor (CMOS) technology compatible process. Moreover, the Si nanowire-based device achieved this high capacitance density without sacrificing power performance compared to the planar device.
by Wen Zheng.
Ph. D.

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Xu, Ying. "Fabrication and Characterization of Photodiodes for Silicon Nanowire Applications and Backside Illumination". University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1446313926.

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Мадан, Роман Григорович. "Фотоперетворювачі на основі наноструктурованого кремнію". Bachelor's thesis, КПІ ім. Ігоря Сікорського, 2019. https://ela.kpi.ua/handle/123456789/28855.

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Робота складається з 55 сторінок, 4 розділів та містить 35 ілюстрацій, 24 таблиці та 19 джерел в переліку посилань. Актуальність теми – інтерес до створення гібридних органічних та неорганічних фотоперетворювачів, що мають більш низьку вартість, ніж традиційні. Метою роботи є дослідження вольт-амперних характеристик фотоперетворювачів. Порівняння характеристик пористого кремнію, отриманого за різного часу травлення. Об’єкт дослідження – фотоперетворювачі на основі наноструктурованого кремнію. Предмет дослідження – методи одержання та морфологія наноструктурованого шару оксиду індію й олова, а також плівки меланіну.
The work consists of 55 pages, 4 sections and contains 35 illustrations, 24 tables and 19 sources in the list of references. The actuality of the topic is the interest in the creation of hybrid organic and inorganic photoconductors that have a lower cost than traditional ones. The purpose of the work is to study the volt-ampere characteristics of nanostructured silicon solar cells. Comparison of the characteristics of porous silicon obtained at different times of etching. The object of research is nanostructured silicon solar cells. Subject of research - methods of obtaining and morphology of nanostructured layer of indium and tin oxide, as well as melanine films.

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Togonal, Alienor. "Silicon Nanowires for Photovoltaics : from the Material to the Device". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX032/document.

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Les cellules solaires à base de nanofils de silicium offrent une alternative intéressante pour la réalisation de panneaux photovoltaïques à haut rendement et à faible coût. Elles bénéficient notamment des excellentes propriétés optiques des nanofils qui forment une surface à très faible réflectivité tout en piégeant efficacement la lumière. Dans cette thèse, nous utilisons et améliorons une méthode de gravure chimique peu coûteuse et industrialisable pour la fabrication de forêts de nanofils de silicium. En adaptant la mouillabilité du substrat et des nanofils, nous avons remédié au problème d'agglomération inhérent à cette méthode lorsqu’on veut obtenir des forêts denses et désordonnées de nanofils. En combinant cette méthode de gravure chimique à la lithographie assistée par nanosphères, nous avons pu fabriquer des réseaux ordonnés de nanofils avec un contrôle précis des propriétés géométriques (diametre des nanofils et distance entre eux). Les propriétés optiques de ces réseaux ont été étudiées théoriquement et expérimentalement afin d'identifier les configurations optimales. Nous avons ensuite fabriqué des cellules solaires à partir de ces différents types de nanofils et deux types de structures. Le premier type, des cellules solaires HIT (Hétérojonction avec couche mince Intrinsèque) à base de nanofils de silicium, a été fabriqué par RF-PECVD. L'optimisation des conditions de dépôt plasma nous a permis d'obtenir des cellules solaires hautement performantes: rendements de 12,9% et facteurs de forme au-delà de 80%. Le second type, des cellules solaires hybrides, est basé sur la combinaison d'une couche organique et des nanofils de silicium. La caractérisation des cellules fabriquées montre des rendements prometteurs. Enfin, nous présentons des résultats préliminaires pour transférer ces concepts à une technologie couches minces
Silicon Nanowire (SiNW) based solar cells offer an interesting choice towards low-cost and highly efficient solar cells. Indeed solar cells based on SiNWs benefit from their outstanding optical properties such as extreme light trapping and very low reflectance. In this research project, we have fabricated disordered SiNWs using a low-cost top-down approach named the Metal-Assisted-Chemical-Etching process (MACE). The MACE process was first optimized to reduce the strong agglomeration observed at the top-end of the SiNWs by tuning the wettability properties of both the initial substrate and the SiNWs surface. By combining the MACE process with the nanosphere lithography, we have also produced ordered SiNW arrays with an accurate control over the pitch, diameter and length. The optical properties of these SiNW arrays were then investigated both theoretically and experimentally in order to identify the geometrical configuration giving the best optical performance. Disordered and ordered SiNW arrays have been integrated into two types of solar cells: heterojunction with intrinsic thin layer (HIT) and hybrid devices. SiNW based HIT devices were fabricated by RF-PECVD and the optimization of the process conditions has allowed us to reach efficiency as high as 12.9% with excellent fill factor above 80%. Hybrid solar cells based on the combination of SiNWs with an organic layer have also been studied and characterized. The possible transfer of this concept to the thin film technology is finally explored

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Мадан, Роман Григорович. "Органо-неорганічні гібриди на основі меланіну". Master's thesis, КПІ ім. Ігоря Сікорського, 2020. https://ela.kpi.ua/handle/123456789/38762.

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Актуальність теми – інтерес до створення гібридних органічних та неорганічних тонкоплівкових сонячних елементів, що мають більш низьку вартість, ніж традиційні сонячні елементи. Метою роботи є визначення оптимальних технологічних умов створення органічно-неорганічних структур для фотовольтаїчного застосування. Предмет дослідження – органо-неорганічні структури на основі кремнію та меланіну.
The relevance of the topic is the interest in creating hybrid organic and inorganic thin-film solar cells, which have a lower cost than traditional solar cells. The aim of the work is to determine the optimal technological conditions for the creation of organic-inorganic structures for photovoltaic applications. The subject of research - organo-inorganic structures based on silicon and melanin.

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Monnier, Lisa. "Elaboration de masques polymère pour la localisation du silicium poreux". Electronic Thesis or Diss., Orléans, 2024. http://www.theses.fr/2024ORLE1056.

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Abstract (sommario):

Ces travaux portent sur la localisation de la gravure du silicium au moyen de masques polymères résistants à l'acide fluorhydrique, indispensable à la formation du silicium poreux par gravure électrochimique ou par gravure chimique catalysée par métal (MaCE). Pour ce faire, nous avons exploré une méthode d'élaboration des masques « tout-chimie » : la séparation de phases induite par évaporation du solvant (SPIES) dans un mélange de polymères déposé par spin-coating suivie d'une extraction sélective. L'objectif est de réaliser des masques de gravure du silicium sans avoir recours à une étape plasma et présentant des ouvertures sub-micrométriques. Cette méthode bien que rapide et facile à mettre en œuvre, met en compétition des phénomènes thermodynamiques et cinétiques complexes déterminant la morphologie finale (i.e. après séchage) des films polymères. La compréhension des mécanismes mis en jeu et le choix judicieux des paramètres expérimentaux ont permis de réaliser des matrices polymères perforées régulièrement mais également des domaines discrets avec des dimensions sub-micrométriques. Des gravures électrochimiques du silicium ont été réalisées à travers ces masques en optimisant la densité de courant et la composition de l'électrolyte. Le caractère protecteur des masques a été évalué et a mis en évidence le fait que la séparation de phases secondaire inhérente à la méthode de structuration des masques, peut créer des chemins de percolation que peut emprunter l'électrolyte et le courant électrique et réduire l'imperméabilité du masque. Bien que le caractère protecteur des masques soit limité pour la gravure électrochimique, ils se révèlent prometteurs pour la formation de silicium poreux par MaCE. Ce procédé a été mis en œuvre par argent et par or au travers des masques et a permis de structurer des micro-colonnes et des micro-piliers ouvrant la méthode SPIES à de nouvelles applications
This work deals with the localisation of silicon etching by using polymer masks resistant to hydrofluoric acid, which is indispensable for the formation of porous silicon by electrochemical etching or metal-assisted chemical etching (MaCE). For this purpose, we explored for producing “all-chemical” masks: solvent evaporation-induced phases separation (SEIPS) in a spin-coated polymer blend followed by selective extraction. The main objective is to produce silicon etching masks without the need for a plasma step with sub-micrometre apertures. Although this method is quick and easy to implement, it involves complex thermodynamic and kinetic phenomena in competition that determine the final morphology (i.e. after drying) of the polymer films. By understanding the mechanisms involved and choosing the right experimental parameters, we were able to produce regularly perforated polymer matrices as well as discrete domains with sub-micrometric dimensions. Electrochemical etchings of silicon were performed through these masks by optimising current density and electrolyte composition. The protective property was assessed, highlighting the fact that the secondary phase separation, inherent in the mask structuring method, can create percolation paths. The electrolyte and the electric current can flow through those percolation paths, reducing the impermeability of the mask. Although the protective property of the masks is limited for electrochemical etching, they are promising for the formation of porous silicon by MaCE. The process has been implemented using silver and gold through the masks and enables micro-columns and micro-pillars to be structured, opening up the SPIES method new applications

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12

Artoni, Pietro. "Silicon Nanowires by Metal Assisted Etching". Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1431.

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Abstract (sommario):

Group-IV semiconductor nanowires (NWs) are attracting interest among the scientific community as building blocks for future nanoscaled devices. Different techniques are currently used for Si NWs preparation, the bottom-up vapor-liquid-solid (VLS) mechanism or the top-down approach which uses the electron beam lithography (EBL). Moreover, literature shows that in the last few years Metal-assisted chemical etching (MACEtch) has become a powerful technique to obtain high density and low-cost Si NWs with high and controllable aspect ratio. It consists of an etching of a Si substrate in a solution containing dihydrogen peroxide, hydrogen fluoride and a metallic salt. Instead of using metallic salts as catalysts (which leave metallic dendrites over the NWs after the etching process), ultrathin films of gold or silver have been evaporated at room temperature on a Si surface, and then etching has been performed. By using for the first time ultra thin films of gold or silver as catalysts for the etch, their main size becomes less than 10 nm, allowing quantum confinement effects. A Si core - SiO2 shell structure is obtained and it is possible to tune the core of the NWs scaling them down to 5 nm. Both energy filtered TEM analyses and Raman analyses strictly confirm these data. Also, a more complex system has been realized, indeed by etching a multi quantum well made by stacks of 1 nm thick Ge and 54 nm thick Si it is possible to fabricate Si/Ge MQW NWs. In this way a structure made of Si NWs which confines carriers in two dimensions (leaving them free on the third one), and a structure of Ge dots (which confines carriers in three dimensions) can be obtained. In literature, a Si NWs system which is natively suitable for photonics is still lacking. All the attempts made by oxidizing VLS grown or EBL made silicon nanowires reported in literature gave poor results. Obtaining light from Si NWs at room temperature under optical and electrical pumping is still a big challenge and would have a tremendous impact on silicon photonics. This thesis demonstrates that both MACetch Si NWs and Si/Ge MQW NWs are suitable for photonic applications. It will be shown a detailed and complete study of the excitation and de-excitation properties as a function of the temperature and of the pump power, determining the excitation cross section, and both presence and origin of possible non-radiative phenomena. A light emitting device based on Si NWs has been realized, showing the efficient electroluminescence emission at room temperature in the red (700 nm) under low voltage pumping. Finally, we realized Si/Ge NWs by the same synthesis approach, in order to obtain different confined structures of both Si and Ge inside each NW. Photoluminescence emission properties of Si/Ge NWs have been studied at room temperature. The last part of the thesis deals with the optical trapping of the single MACetch Si NW. Optical trapping (OT) of nanostructures has acquired tremendous momentum in the past few years. Manipulating nanoparticles with OT is generally difficult because radiation forces scale approximately with particle volume and thermal fluctuations can easily overwhelm trapping forces at the nanoscale. Hence, the role of size-scaling is crucial for understanding the interplay between optical forces and hydrodynamic interactions that change dramatically with size, therefore much affecting both force-sensing and spatial resolution in precision applications. A detailed study on how optical trapping and Brownian motion of very thin Si NWs depending on their size has been performed. The NWs length is the key parameter that regulates forces, torques, and hydrodynamics. The core of the last chapter fully characterizes the three-dimensional translational and angular Brownian motion, deals with the measure of the root-mean-square displacements and shows the different size-scaling due to the interplay between radiation forces defining the trapping potential and hydrodynamics.

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13

Mörsdorf, Alexander. "Metal-assisted etching of nanopores in silicon". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177359.

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Abstract (sommario):

Nanoporous membranes are an interesting approach to manufacture a variety of devices for different applications. For example in biomedicine the separation of molecules or cells or the sequence-based analysis of single-stranded DNA are of great interest. Based on silicon membranes, a promising method to achieve pores with a high aspect ratio is metal-assisted etching, where noble metal particles serve as catalysts for the oxidation of the underneath Si, which is subsequently removed by hydrofluoric acid. This thesis project deals with developing a method, based on wet chemical etching of nanopores into a silicon membrane, utilizing noble metal particles as catalysts. The main goal was to investigate if it is possible to achieve straight channels perpendicular to the substrate surface with approximately the same diameter as the particle size. Therefore, the etching behaviour of gold, silver and platinum nanoparticles with different diameters on various substrates and etching solutions has been investigated. First the optimal substrate and etching solution for defined pore growth were determined using gold nanoparticles. Long-time measurements have been conducted showing a saturation of the etch speed and square aperture growth after a few hours. Next the etching reaction was enhanced with adding HCl and applying a voltage and it was found that the particle concentration has an influence on the orientation of the pores. After showing only erratic movement in the beginning, erect pores with a maximum aspect ratio of ~ 20 could be manufactured using CTAB coated particles. After that silver particles have been investigated. Initially, the optimal compositions for synthesis and etching solution were determined. Then the behaviour for long-time immersion was investigated, implicating that the pores grow fast and constantly within the first hour. In the end, highly straight pores with aspect ratios of ~ 1000 were etched. But due to the high particle concentration, the surface was badly affected by strong etching, as well. For both noble metals, diluting the etching solution and thus slowing down the etching reaction resulted in more oriented pore growth. For the platinum particles, however, no promising results could be achieved, because platinum seems to be a too strong catalyst for the etching reaction.

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14

Tamburi, Marco. "Caratterizzazione della superficie di array di nanofili di silicio". Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/6154/.

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Abstract (sommario):

Nel primo capitolo viene introdotto lo studio eff�ettuato e descritto un metodo di misure successivo alla caratterizzazione della super�ficie. Nel secondo capitolo vengono descritti i campioni analizzati e, nello speci�fico, la crescita attraverso MaCE dei nanofi�li di silicio. Nel terzo capitolo viene descritto lo strumento AFM utilizzato e la teoria della caratterizzazione alla base dello studio condotto. Nella quarta sezione vengono descritti i risultati ottenuti mentre nelle conclusioni viene tratto il risultato dei valori ottenuti di RMS roughness e roughness exponent.

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15

Chang, Shih-wei Ph D. Massachusetts Institute of Technology. "Fabrication of high aspect ratio silicon nanostructure arrays by metal-assisted etching". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59214.

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Abstract (sommario):

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Includes bibliographical references (p. 167-178).
The goal of this research was to explore and understand the mechanisms involved in the fabrication of silicon nanostructures using metal-assisted etching. We developed a method utilizing metal-assisted etching in conjunction with block copolymer lithography to create ordered and densely-packed arrays of high-aspect-ratio single-crystal silicon nanowires with uniform crystallographic orientations. Nanowires with sub-20 nm diameters were created as either continuous carpets or as carpets within trenches. Wires with aspect ratios up to 220 with much reduced capillary-induced clustering were achieved through post-etching critical point drying. The size distribution of the diameters was narrow and closely followed the size distribution of the block copolymer. Fabrication of wires in topographic features demonstrated the ability to accurately control wire placement. The flexibility of this method will facilitate the use of such wire arrays in micro- and nano-systems in which high device densities and/or high surface areas are desired. In addition, we report a systematic study of metal-catalyzed etching of (100), (110), and (111) silicon substrates using gold catalysts with varying geometrical characteristics. It is shown that for isolated catalyst nanoparticles and metal meshes with small hole spacings, etching proceeded preferentially in the <100> direction. However, etching was confined in the direction vertical to the substrate surface when a catalyst mesh with large hole spacings was used. This result was used to demonstrate the use of metal-assisted etching to create arrays of vertically-aligned polycrystalline and amorphous silicon nanowires etched from deposited silicon thin films using catalyst meshes with relatively large hole spacings. The ability to pattern wires from polycrystalline and amorphous silicon thin films opens the possibility of making silicon nanowire-array-based devices on a much wider range of substrates. Finally, we demonstrated the fabrication of a silicon-nanopillar-based nanocapacitor array using metal-assisted etching and electrodeposition. The capacitance density was increased significantly as a result of an increased electrode area made possible by the catalytic etching approach. We also showed that the measured capacitance densities closely follow the expected trend as a function of pillar height and array period. The capacitance densities can be further enhanced by increasing the array density and wire length with the incorporation of known self-assembly-based patterning techniques such as block copolymer lithography.
by Shih-wei Chang.
Ph.D.

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16

Anokhina, Ksenia. "Investigation of Metal-assisted Si Etching for Fabrication of Nanoimprint Lithography Stamps". Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-14459.

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Abstract (sommario):

This diploma thesis deals with the investigation of the metal-assisted catalytic etching (MaCE) of Si. One of the main goals is to study fabrication of stamps for nanoimprint lithography using MaCE. Formation of nanoporous silicon (PSi), Si nanowires (SiNWs) and three-dimensional nanostructures in Si by MaCE is demonstrated. For this purpose optical lithography, electron beam lithography (EBL), shadow mask evaporation and aerosol nanoparticles deposition techniques have been utilized. The etching rate and surface morphology of Si (with Au lift-off films as a catalyst) as functions of time and concentrations of chemicals are measured in the current diploma work using optical microscope and scanning electron microscopy (SEM). In the current thesis it is shown that Si structures with sub-150 nm lateral sizes, high aspect ratio (up to 1:21), well-defined shapes, and various complexity can easily be fabricated by means of MaCE process.

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17

Greil, Stefanie Margita. "In situ Photolumineszenz bei Ätzprozessen zur Nanostrukturierung von amorphem und kristallinem Silicium". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16843.

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Abstract (sommario):

Die vorliegende Arbeit beschäftigt sich mit Ätzprozessen von alkalischen und insbesondere HF/HNO3-basierten Ätzmedien an Silicium (Si). Es wurden Ätzprozesse an kristallinen (c-Si) und besonders an amorph/kristallinen (a-Si:H/c-Si) Silicium-Strukturen mit Hilfe von in situ Photolumineszenz(PL)-Messungen untersucht. Diese ermöglichen eine Verfolgung der Veränderung der Grenzflächendefektdichte an der c-Si-Grenzfläche während der Ätzprozesse. Es wurde erstmals beobachtet, dass der über Ladungsträgerinjektion von Löchern in das Si ablaufende Ätzprozess in HNO3-reichen, HF/HNO3-basierten Ätzmedien eine temporäre Feldeffektpassivierung an der geätzten Grenzfläche verursacht, welche zu einer Verzögerung des eigentlichen Auflöseprozesses des Si führt. Die Anwendung dieser Ätzmedien erfolgte im Rahmen der Strukturierung von a-Si:H-Schichten auf c-Si zur Realisierung von interdigitierenden Kontaktstrukturen rückseitenkontaktierter a-Si:H/c-Si-Heterosolarzellen. Für diese Ätzprozesse konnte mit Hilfe von in situ PL-Messungen erstmalig eine in situ Prozesskontrolle etabliert werden. Der Ätzprozess kann exakt bei Erreichen der a-Si:H/c-Si-Grenzfläche gestoppt werden, wodurch die ätzbedingte Defektbildung an der resultierenden c-Si-Oberfläche minimiert wird. Als weiterer Themenschwerpunkt wurde eine Photolithographie-freie Nanostrukturierung von a-Si:H/c-Si-Strukturen durch metallkatalysiertes Ätzen (MAE) vorgestellt, wobei MAE erstmals auf a-Si:H angewandt wurde. Anhand von in situ PL-Messungen konnte ebenfalls eine, wenn auch geringere, Feldeffektpassivierung an der geätzten Grenzfläche im Zuge der Injektion von Löchern in das Si durch die katalytisch aktiven Ag Nanopartikel (AgNP) beobachtet werden. Mit den so steuerbaren MAE-Prozessen können a-Si:H-Schichten exakt bis zur a-Si:H/c-Si-Grenzfläche punktuell geöffnet werden. Auf diese Weise wurden p-Typ a-Si:H/c-Si-Heterosolarzellen mit einem punktförmigen Absorberkontakt erfolgreich realisiert.
This dissertation is concerned with wet chemical etching processes of silicon (Si) by alkaline and especially HF/HNO3 based etchants. The etching processes are applied to crystalline (c-Si) and amorphous/crystalline (a-Si:H/c-Si) samples and analyzed by in situ photoluminescence (PL) measurements. These measurements enable a monitoring of changes in the defect density at the c-Si interface during the etching processes. By etching of Si in HNO3-rich HF/HNO3 based etchants, a temporary field effect passivation at the etched c-Si surface by hole injection was established. It was detected by in situ PL measurements for the first time. This effect causes a delay of the actual dissolution of the Si. These etching processes were applied to structure a-Si:H layers on c-Si in order to establish interdigitated contacts for back contacted a-Si:H/c-Si heterojunction solar cells. A process control for that kind of etch back processes was developed for the first time by in situ PL measurements. This method enables an exact termination of the etching processes with the arrival of the etching front at the a-Si:H/c-Si interface. Thus, etching induced defects at the resulting c-Si surface can be reduced. Finally this thesis focuses on the development of a photolithography-free approach for nanostructuring of a-Si:H/c-Si samples using metal assisted etching (MAE). In this context, MAE was applied to a-Si:H for the first time. In situ PL measurements also showed a temporary field effect passivation during MAE due to hole injection by the catalytically active Ag nanoparticles (AgNP). Here, this effect was less distinct because of only punctual etching by the AgNP. These designed MAE processes are used to selectively etch a-Si:H layers exactly down to the a-Si:H/c-Si interface. This process opens new doors to a novel fabrication technique for point contacted heterojunction solar cells. P-type a-Si:H/c-Si heterojunction solar cells with point contacted back surface field are presented.

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18

CARA, ELEONORA. "Tailored fabrication of nanostructured substrates for surface-enhanced Raman spectroscopy applications". Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2735516.

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19

Ko, Pei-Ju, e 柯佩汝. "Thermoelectric properties of silicon nanowires fabricated using metal-assisted chemical etching". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/17597510189977822200.

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Abstract (sommario):

碩士
國立中央大學
材料科學與工程研究所
103
The thermal conductivity of bulk silicon is 150Wm-1K-1 at room temperature. It is considered as poor thermoelectric material. The ZT is just 0.01 due to its high thermal conductivity. Thus, one dimensional nanostructure has become a good study to solve this problem. Comparing with bulk, there have large surface to volume ratio of one dimension nanostructure. The thermal conductivity reduced by the phonon scattering in the boundary of nanowires. It is helpful to reduce the thermal conductivity. In our study, we use MACE method to fabricate single rough silicon nanowires from lightly doped p-type and heavily doped n-type (100) wafers. The diameter of silicon nanowires are about 150-250nm. The thermal conductivity was decreasing obviously. After oxygen plasma etching, the electric conductivity was increased for lightly doped silicon nanowires.

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20

Wen, Shu-Ning, e 温書寧. "Silicon Nanostructures Prepared by Metal-assisted Chemical Etching for SERS Application". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/33315625632731698512.

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Abstract (sommario):

碩士
國立聯合大學
材料科學工程學系碩士班
101
Scientists have distinguished weak Raman signals of molecules from different structures of substances. To enhance the Raman signals, using precious metal nanoparticles such as gold and silver, which can induce the surface plasmon resonance (SPR) by external electric field, has been developed to increase the specimen surface area. This technique is called surface-enhanced Raman scattering (SERS). There are various methods used to produce nanostructures for SERS application. In this study, we applied low-cost metal-assisted chemical etching (MACE) to produce large-surface-area nanowall structures with sub-micron thickness on silicon wafer. After depositing Ag nanoparticles on the 400-nm-thick nanowalls (which is much thinner than the typical thickness from MACE), the enhancement factor (EF) can reach 10^9.

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21

LEE, WEN-LING, e 李玟怜. "Introducing Current-driving Method to Metal-assisted Chemical Etching of Silicon". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/35mcxh.

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22

Lai, Ming-Hung, e 賴明宏. "Enhanced metal-assisted chemical etching on silicon by localized surface plasma resonance". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/69586029075337167541.

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Abstract (sommario):

碩士
國立清華大學
光電工程研究所
101
In recent years, since silicon nanostructures have many unique qualities, they have been applied to a wide variety of areas, including optoelectronic devices, biological, semiconductor optical devices, optical-sensing devices and solar cells. In this thesis, metal-assisted chemical etching of silicon incorporating localized surface plasma resonance was studied. The basic idea is that the etching rate is influenced by the light illuminating on the metal nanoparticles. Several case studies were carried out to examine the etching rate, including different content of the chemical etching solution, the vapor chemical etching method, and light sources with different wavelength bands. SEM images are taken to characterize the silicon nanopores, etching rate and so on. Via the experimental results, we concluded the localized surface plasmon (LSP) on the metal nanoparticles will affect the etching rate very much. These strong LSP modes increase the light absorption of Si, resulting in a large amount of holes injected in the silicon. It can explain why the etching speed was greatly enhanced and was wavelength dependent.

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23

Wang, Po-Sheng, e 王柏盛. "Fabrication and Wettability of gradient porous silicon by silver metal assisted chemical etching". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/v3uw9w.

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Abstract (sommario):

碩士
國立中央大學
能源工程研究所
107
In recent years, nanoporous silicon plays an important role in the semiconductor industry and energy industry. Two-step metal assisted chemical etching method has the advantages of low cost and simple processes. In biomedical and microfluidic systems, the hydrophobicity of materials must be considered. We can control a fluid drop to move on a solid surface by changing the hydrophobicity of surface material with nano structures. We deposit silver particles with electro-less plating deposition method, followed by the anisotropic etch of the silicon surface by oxidation of etchant and silver particles. We apply different temperature to see how it affects the etching depths and the structures. Appropriate temperature helps to achieve best etching depth and porousity. We also determine the effects of different surface structures on droplet contact angles. We find that the driving force to make the droplet move is too small on the nano porous silicon surface we made. So we use a tilt platform to increase the driving force to observe the effects easily. The critical angle at the larger contact angle side is smaller than the one at the smaller contact angle side, and is faster in the increase of the acceleration of the droplet.

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24

Sahoo, Mihir Kumar. "Transfer of Vertically Aligned Silicon Nanowires Array Fabricated Using Metal-assisted Chemical Etching". Thesis, 2022. http://ethesis.nitrkl.ac.in/10294/1/2022_PhD_MKSahoo_517EE1001_Transfer.pdf.

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Abstract (sommario):

Bulk silicon (Si) possesses an indirect bandgap and low surface area to volume Si ratio. Silicon nanowires (SiNWs), a derived material of Si, overcomes the drawbacks of Si and promises improvement in energy conversion (e.g., solar cell) and storage (e.g., lithium-ion battery) devices, gas sensors, medical diagnostics, drug delivery. The SiNWs-based devices have optical, electronic, and physical properties that can outperform their traditional counterparts in various ways because the SiNWs have a high surface Si area to volume ratio and unique quasi-one-dimensional electronic structure. The metal-assisted chemical etching (MACE) produces the SiNWs using an electrolyte composed of hydrofluoric acid (HF), hydrogen peroxide (H2O2), and a metal salt. Effect of MACE parameters, such as H2O2 concentration (i.e., 0.1 M to 0.3 M), etching time (i.e., 30 minutes to 60 minutes), Si wafer resistivity, HF concentration (i.e., from 0.48M to 9.6M), and etching temperature (i.e., 25℃ to 85℃), on the morphological characteristics (especially length) of SiNWs are compared and thoroughly discussed. Additionally, MACE parameters on the length of SiNWs using Si and porous Si substrates are discussed. The cross-sectional view of FESEM confirms the variation of the length of SiNWs for the variation of MACE parameters. The Raman line broadening and peak shift are due to FANTUM (FANo + quanTUM) effect (i.e., Fano effect and quantum confinement effect), amorphous content (⁓15-20%), and stress in the SiNWs. The tensile strain remains ⁓0.25%, and the crystallinity volume fraction of ⁓80% provides a range of MACE parameter variation to fabricate the SiNWs according to various device applications. The SiNWs, however, need to be transferred to a better substrate for additional flexibility, lesser cost, and transparency compared to Si substrate resulting in improved device functionality. This part explores, optimizes, and compares two techniques to transfer SiNWs to glass: the gluing technique and the two-step electro-assisted technique. The objective is to preserve the length of nanowires on a larger transfer area. Gluing technique spin-coats an adhesive layer made of polyvinyl acetate (PVAc) and methanol solution. The gluing method studies the effect of variation in MACE time on the percentage transfer ratio for the optimized PVAc layer. The electro-assisted technique detaches the vertically aligned SiNWs array with the aid of a sacrificial porous Si layer for variation in anodization time. The yield of the gluing and electro-assisted technique is optimized for MACE and anodization time. The transferred layer is characterized by various parameters, such as the percentage transferred length (%TRL), total transfer area, crystallinity, strain, and morphology of the SiNWs. For optimized values, the gluing method achieved %TRL = 68.2% while transferring 0.95 cm2 of the film area, whereas the electro-assisted technique achieves %TRL = 7.4% for an area of 19 cm2.

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25

Chang, Chia-Feng, e 張家逢. "Optimization of surface treatment after forming black silicon by metal-assisted chemical etching method". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/34354978674950272505.

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Abstract (sommario):

碩士
國立臺灣科技大學
化學工程系
104
We optimized the condition in metal-assisted chemical etching in order to obtain the lowest reflection of our black silicon. Meanwhile, we also optimized several cleaning methods to obtain black silicon which has low reflection but high minority carrier lifetime. We found that in our condition, reflection won’t get lower as the etching time stays longer. Our black silicon has reflection 4% at 600nm, while the etching time is 135 second. In cleaning part we found that ammonia is not suitable for cleaning black silicon because it causes too much etching to the wafer. Hydrochloric acid and sulphuric acid cause less etching to black silicon. Sulphuric acid has better cleaning ability than the others. We obtained 950μs minority carrier lifetime on our best black silicon and its reflection is 5% (at 600nm). Eventually we apply to KOH textured silicon wafer. We obtained 684μs minority carrier lifetime and reflection 5% at 600nm. Compare with wafers only textured by KOH, we lowered the reflection by 8% and the minority carrier lifetime recovered by 61%.

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26

Chiu, Chia-Chen, e 邱嘉辰. "Using Metal-assisted Chemical Etching to Enhance the Performance of Silicon Nanopillar Solar Cells". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/22311864266205397470.

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Abstract (sommario):

碩士
國立聯合大學
材料科學工程學系碩士班
103
In this study we adopted p-type silicon wafers as substrates and used semiconductor technology of lithography and plasma dry etching to produce three different sizes of array structures on the silicon substrate. These array structures were doped with phosphorus to form p-n junction on the surface by ion implantation; the implantation dosage was fixed and the values of implantation energy were varied to seek a suitable parameter for device performance. An aluminum coating was prepared by sputtering as a backside electrode, and silver paste was used as the front side electrode. The performances of array devices were evaluated by a sun light simulator under AM1.5 condition. In the second part of this thesis, we developed a metal-assisted chemical etching to create nanostructures on these array structures, which increased the absorption by lower surface reflection to enhance the photoelectric conversion efficiency of solar cells. Analyses by field emission electron microscopy, total reflectance measurement, and the photoelectric conversion efficiency were carried out in these two parts. The results showed that the in the first part, for three columnar structures with 400, 1000, and 5000 nm, the photoelectric conversion efficiency were 11.33%, 10.35%, 9.36%, respectively, and a columnar array structure with 400 nm feature can be significantly increased 35.85%; in the second part of the wet etching, the result shows that the efficiency of 5000-nm device was improved 5.75% after etching, and for 1000-nm array the efficiency was increased 6.1%.

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27

PAN, XIANG-QIN, e 潘詳親. "Manufacturing and Thermal Property Analysis of Porous Silicon Structure by Metal Assisted Chemical Etching". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/z9zg43.

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Abstract (sommario):

碩士
國立中央大學
機械工程學系
106
Nanoporous material has been widely used in various applications. It has high area-to-volume ratio that increases surface area and can be used in gas sensors, mass spectrometers, mass-transferring films, and anti-reflection coating on solar panels. Due to the increasing porosity and the size effects of nano-structures, it leads to an effective decreasing in the heat conduction coefficient and makes it a good thermal insulating material. Typical porous silicon fabrication processes include electrochemical etching, dry etching, and metal-assisted chemical etching. Among them, metal-assisted chemical etching has the advantages of simple process and low equipment cost. In this study, we use metal-assisted chemical etching to prepare high aspect ratio nanoporous silicon, explore the relation between etching parameters and porosities, and analyze its heat conduction properties. The silver nitrate solution and hydrofluoric acid were used to form the Ag nanoparticles on silicon surface as the catalyst for etching. The anisotropic etching was performed in the etching solution with hydrogen peroxide to form nanoporous structures. A well-distributed nanoporous structure was achieved through controlling the concentration of hydrogen peroxide. The results showed that for a long etching time, the etching rate became slower and the porous layer growth rate gradually decreased due to the etching on top structure. Different heat transfer models were used to analyze the thermal transfer coefficient. The results showed for the simplified models that do not consider the pore size exhibited a significant difference in thermal conductivity for small pore size samples. Considering of dependence of porosity and pore size in the process perspective, the effective thermal conductivity was lower than expected due to the impact of the small pore size structure.

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28

Li, Hong Ching, e 李鴻慶. "Fabrication of Multicrystalline Silicon Solar Cells with Surface Texturing by Metal-Assisted Chemical Etching (MAE)". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/60851818079493496075.

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碩士
國立清華大學
電子工程研究所
100
In this thesis, the surface texturing for multicrystalline silicon by using metal-assisted chemical etching (MAE) method was carried out to fabricate solar cell. There were two kinds of etchant used in the MAE process. One was a mixture of HF, H2O2 and H2O and the other was a mixture of HF, Fe(NO3)3 and H2O. The metal used in the MAE process was Ag. The textured surface morphologies were analyzed by SEM and reflectance measurement. The different morphologies including bowl, cone and grating with high aspect ratio were fabricated. The average reflectance of textured surface is below 10% and the lowest reflectance is about 2~3% in the range of 400~600 nm. The efficiency of solar cell fabricated with HF/Fe(NO3)3/H2O is 8.24% and fabricated with HF/H2O2/H2O is 11.81%.

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29

Cheang, Jia-Kang, e 鄭家康. "Fabricating High Aspect Ratio Silicon Micro-Holes Implemented by Metal-Assisted Chemical Etching with Taguchi Analysis". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/24768390488648287008.

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碩士
國立清華大學
材料科學工程學系
102
High aspect ratio (AR) Silicon base structure plays an important role in semiconductor industry. Recent advances in small size and multifunctional chip has made the increased demands of fabrication of micro and nano scale high AR silicon structure. However, the commercial fabricating method, deep reactive ion etching (DRIE) suffers from high cost and complex processing due to the high maintenance fees and complicated set up. In contrast, we investigate the ability of promising novel chemical etching, metal assisted chemical etching (MACE) that can etch Silicon (Si) wafer in <100> direction near room temperature and thus benefits from it’s simple and cost effective reaction process. In order to fabricate high AR silicon micro holes structure, we have optimized our MACE recipe by employing statistical Taguchi L9 method and ANOVA analysis. Subsequently, the post-MACE formed Si wires have been removed by furnace oxidation followed by Hydrofluoric acid (HF) treatment. Therefore, high AR Si micro holes structure with smooth surface is obtained. Our results demonstrate that the AR value is up to 13 (for 4x4um square arrays in p-type (100) Si substrate), and the etching rate of optimal condition is about 3 µm/min. Moreover, an alternative method that possess larger throughput for fabricating high AR Si micro structure has been performed. Besides, it is believed that the AR value can be further improved by increasing the thickness of Si nitride layer (protection layer), using stronger protection layer instead, and exploring the method that can well-control the morphology of metal catalyst which strongly influence the post-etched structure.

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30

Sheng-ChiaYu e 尤勝加. "Metal-assisted Chemical Etching of High Aspect Ratio Silicon Nanostructures for Highly Efficient Capture of Bladder Epithelial Cancer Cells". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/bnmss5.

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31

Tsao, Chiao-Heng, e 曹巧姮. "Fabrication of Silicon Nanowire Array Through the Metal-induced Wet Chemical Etching Method and Its Photovoltaic Properties". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/87917143123478414382.

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碩士
國立清華大學
材料科學工程學系
99
Large area SiNW arrays were successfully prepared by immersing a silicon wafer into an aqueous solution of AgNO3 and HF in an electroless metal deposition (EMD) process. However, in the process the Ag clusters easily aggregated, forming large Ag particles of various sizes, which in turn resulted in silicon wires with a large size distribution. To improve the uniformity of the SiNW arrays, uniform dispersed gold nanoparticles were used as the cathode instead, followed by the etching process using H2O2/HF solution. The growth conditions, morphologies and anti-reflection properties of SiNW arrays have been studied. Ultraviolet-visible spectroscopy analysis reveals that the SiNW has remarkable anti-reflection property, as compare with the plane silicon wafer. The reflectance of SiNW is found to decrease with increasing reaction time. The simple, inexpensive and easily scalable process to fabricate a large area silicon anti-reflection surface is a promising process for silicon-based solar cell. We used the synthesized SiNWs to fabricate solar cells. According to current-voltage curve and monochromatic incident photon-to-electron conversion efficiency(IPCE) analysis, we knew that there are many defects on the SiNW surface, which can act as recombination centers and enhance the surface recombination rate. Therefore, only the SiNW solar cell with appropriate length, which is enough to trap light but not too long for cause serious recombination, shows better performance than planer-Si solar cell.

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32

Chang, Jai-Wei, e 張家瑋. "Making silicon nanowire structure with metal-assisted etching". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/31273698108260668090.

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碩士
元智大學
光電工程研究所
98
Finding alternative energy sources is an urgent issue. Solar cells based on silicon technology is one of the most promising solution because of its relatively low cost, even though its energy efficiency is not high. To enhance its competitiveness, researchers continue to seek for ways to increase its efficiency and anti-reflectivity. Among the numerous methods to reduce surface reflectivity and increase light-trapping, making surface nanostructure is found to be simple and low-cost. This study investigates the surface morphology of silicon substrate, subjected to metal-assisted etching mechanism with various silver deposition thickness and etching time. The reflectance spectra inside the integrating sphere with normal and oblique incident light are measured to study the effect on the reflectivity. Specifically, the silver deposition thickness is chosen in the range of 10–80 nm, whereas the etch time is set to the range of 5–40 minutes. The result shows that the surface is full of holes and craters in nano scale for the case of silver deposition thickness thinner than 30 nm, whereas the surface is full of nano-wire structure for the thicker case. Both cases have the lower reflectivity, compared to ordinary silicon substrate surface. However, surfaces with holes and craters have lower reflectivity than the surface with nano-wires. Also, reflectivity with 30° and 45° incident angle is lower than that with 0° and 60°. Using the technique, with the addition of nanosphere lithography, a periodic surface nano structure can be made. With different pitches and sizes, a functional surface with either anti-reflection or anti-internal reflection can be realized for solar cell and light emitting diode applications, respectively.

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33

Chong, Teck Kong. "Analysis and characterization of silicon textured by metal assisted etching technique". Phd thesis, 2015. http://hdl.handle.net/1885/149909.

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The efficient reflection suppression of a solar cell over a broad spectral range can be achieved by nano-scale surface textures. The fundamental reason is that the textured surface behaves like an effective medium with graded refractive index, resulting - in the optimal case - in vanishing reflectivity and appearing black under sunlight. The surface morphology is commonly known as "black Silicon" or bSi. Various methods for fabricating bSi have been developed such as reactive ion etching (RIE), metal-assisted etching (MAE) and laser texturing. MAE appears to be an interesting method because it is a flexible and potentially simple process for producing bSi. In fact, highly efficient bSi solar cells have been reported recently. Nevertheless, the energy conversion efficiency of these cells is still well below the highest achievable efficiencies. The high aspect ratio and surface area of the bSi can result in high rates of surface recombination, and therefore high values of Seff on the resulting structure. Nonetheless, no results of a systematic investigation of the correlation between optical performance, surface area increase and Seff in silicon have been reported to the best of author's knowledge. Another reason for the lower-than-optimal performance of the cells is the poor metal contact that contributes to the series resistance of the cell. Potential origins of this detrimental effect have only briefly been investigated through visual inspection, and measurements of the contact resistivity have not been made. In this thesis, an alternative 3-step MAE texturing technique which produces nanoporous silicon (MAE nSi) will be investigated using Silver (Ag) and Palladium (Pd) as catalyst. The thesis consists of two parts, namely experimental investigations and modelling. Both Ag and Pd are used to produce nano-scale structures. The optical properties of the nSi surfaces produced using these two metals are shown to be very similar. The majority of the work focuses on Ag due to the demonstrated superior electronic properties of the resulting samples. The investigation of Ag textured MAE nSi extends from basic optical performance to the effect on optical performance of high temperature process steps, initial surface roughness, the addition of a dielectric coating and encapsulation. In addition, the surface passivation and contact quality of Aluminium evaporated contacts on the nS surfaces are investigated. Optical modelling of MAE nSi provides greater insight into the light propagation behaviour of the structure. In this case, focus ion beam (FIB) has been used to acquire SEM images of the surface morphology. The reconstructed surface was then imported into GDCalc software for calculating the reflectance and transmittance matrices which can then be used to further analysis. Light propagation inside the bulk can then be calculated using an incoherent model. The modelling results were then compared to experimental results and also an ideal Lambertian model. Finally the generation profile was obtained. The generation profile is useful for investigating the potential efficiency of a solar cell.

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34

Chou, Li-Hsing, e 周力行. "Fabrication of Nanowire Array by Metal-Assisted Etching and application on N-type Rear-Emitter Silicon Solar Cell". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/01306904942236413162.

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Abstract (sommario):

碩士
國立臺灣大學
化學工程學研究所
100
In the process of solar cell fabrication, the factors of efficiency losses are Short-Circuit losses, Open-Circuit Voltage losses and Fill Factor losses. The Short-Circuit losses combined Reflection losses, Shading losses and absorption losses, Anti-Reflection Coating and Surface Texturing which can reduce the reflection losses to improve the efficiency. Compare with traditional Anti-Reflection Coating, Deep Sub-micron Surface Texturing has potential to replace the former due to its ability of Board-banded low reflectance. N-type crystalline silicon is recently attracted much attention due to higher minority carrier lifetime and toleration of metallic impurity. In this thesis, we fabricate the nanowire array on N-type silicon wafer through assisting of silver ions and analyze its morphology and reflectance. The diameter of nanowire is about 60nm. Finally, we fabricate the nanowire array solar cell and measure its IV character by Solar Simulator and Spectral response by Quantum Efficiency measurement device; we also discuss the effect of rapid thermo process for surface passivation and how different length effect on efficiency. Finally, we use multi-crystalline silicon to fabricate nanowire solar cell and reach the best efficiency to 10％

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35

Wu, Zong Hua, e 巫宗華. "Fabrication of Complex Micro- and Nanostructures using Self-Assembled Diblock Copolymer Templates and Metal-Assisted Chemical Etching". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/63834465506078938528.

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Abstract (sommario):

碩士
國立清華大學
工程與系統科學系
103
This thesis presents a novel integration scheme that can fabricate complex micro-nano hybrid silicon structures. The structures are formed by metal-assisted chemical etching, while microlithography and self-assembled diblock copolymer nano- templates are employed to define their geometries. The nano-templates are made of P(S-b-MMA) copolymer that can self-assemble into arrays of 18-nm-diameter PMMA cylinders hexagonally packed in a PS matrix with a lattice constant of 36 nm. To facilitate the self-assembly process, a thin layer of 3-(p-methoxy-phenyl)propyl- trichloro-silane is coated between P(S-b-MMA) and silicon substrate. Once PMMA is selectively removed, the resulting nanoporous PS film is employed to control the deposition of metal nanodots. In the prototype demonstration either chromium or gold is deposited, while chromium and gold is used as the blocking and catalytic material in the etching process, respectively. Meanwhile, photolithography is employed to realize the micro-patterning of metallic thin films. Throughout the process, reactive ion etching is used repeatedly to clean the substrate surface. Finally, the gold-assisted chemical etching is carried out in a solution consisting of deionized water, H2O2, and HF to produce the desired micro-nano hybrid silicon structures. It is demonstrated that the presented integration scheme is a highly repeatable method to form well-aligned, crystalline silicon nanowires with tunable diameters below 100 nm and microstructures as well. As such, the presented integration scheme can fabricate complex micro-nano hybrid structures, which are desired for a variety of cooling and biological applications.

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36

Chattopadhyay, Soma. "Material characterization, patterning and adsorbate induced modulation of light emission of porous silicon produced by metal-assisted electroless etching /". 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3223559.

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Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006.
Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3816. Adviser: Paul W. Bohn. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

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37

Tsai, Po-Hung, e 蔡帛宏. "Performance Characterization of Si Thin-Film Solar Cells Using Nanopores Surface Structure on the Emitter Layer by Metal-Assisted Chemical Etching". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/262mb9.

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碩士
國立臺北科技大學
光電工程系研究所
102
In this work, the optical and electric properties of silicon thin film solar cell with the nanopores subwavelength structures using metal-assisted chemical etching (MACE) and various TiO2 passivation layers are studied. The experiment is first prepared silicon thin film solar cell, The epitaxial layer consisted of a 5-um N--Si base layer and a 0.87 um P+-Si emitter layer grown on N+-Si substrated by chemical vapor deposition (CVD) system. After cleaning, a 20 nm silver film was deposited on the cells surface by E-beam evaporation and annealed at 300 ℃, 5 min on RTA chamber. Then, the nanopores surface structure on the emitter layer was created by using MACE processing under different etching time. Using SEM images to examine the nanopores state and depth on silicon surface, the optical reflectance, dark and photo I-V, EQE were measured and compared. The reflectance of the fabricated 30s MACE time solar cell is less than 2.5% at 350 – 1050 nm wavelength. The maximum conversion efficiency enhancement of approximately 43% (from 5.64 to 8.07%) was obtained for cell with 10s MACE time, the EQE cutoff point at short wavelength band are exhibited a red shifted (from 375 to 420 nm) when the MACE time increased. Finally, different thickness of the TiO2 passivation layer were deposited on the nanopores of the silicon thin film solar cells, in order to reduce its surface carrier recombination and increase the photocurrent. Dark I-V measurement shows that the idealily factory (n) and saturation current (I0) will reduce with TiO2 the thinkness of incresing. For reflectivity measured, the results are: (1) For bare cell and the Cell with 1s MACE time, the reflectance decreases with the thickness of TiO2 increased, like to a single anti-reflective layer on a device. (2) For MACE time of 5, 10, 15, 30 seconds, the reflectivity decreases when a 15 nm TiO2 deposited; the reflectance will increase when the film thickness of 45 nm TiO2 deposited, particullary at 350 to 650 nm wavelength. For EQE and photonvoltaic I-V measurement, the results are: (1) EQE increases with reflectivity decreased. (2) EQE enhance at short wavelength for bare cell and cell with MACE time of 1s was obtained, when the cell deposited TiO2 layer. However, EQE enhanced at long wavelength for cell with MACE time of 5s、10s、15s、30s. Finally, we demonstrated a thin-film Si solar cell with MACE time of 15s and 30 nm TiO2, having the efficiency enhancement of approximately 73.2 % (from 5.64 to 9.77%).

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