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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Electronic noise in nanostructures: limitations and sensing applications

Kim, Jong Un 25 April 2007 (has links)
Nanostructures are nanometer scale structures (characteristic length less than 100 nm) such as nanowires, ultra-small junctions, etc. Since nanostructures are less stable, their characteristic volume is much smaller compared to defect sizes and their characteristic length is close to acoustical phonon wavelength. Moreover, because nanostructures include significantly fewer charge carriers than microscale structures, electronic noise in nanostructures is enhanced compared to microscale structures. Additionally, in microprocessors, due to the small gate capacitance and reduced noise margin (due to reduced supply voltage to keep the electrical field at a reasonable level), the electronic noise results in bit errors. On the other hand, the enhanced noise is useful for advanced sensing applications which are called fluctuation-enhanced sensing. In this dissertation, we first survey our earlier results about the limitation of noise posed on specific nano processors. Here, single electron logic is considered for voltage controlled logic with thermal excitations and generic shot noise is considered for current-controlled logic. Secondly, we discuss our recent results on the electronic noise in nanoscale sensors for SEnsing of Phage-Triggered Ion Cascade (SEPTIC, for instant bacterial detection) and for silicon nanowires for viral sensing. In the sensing of the phage-triggered ion cascade sensor, bacteriophage-infected bacteria release potassium ions and move randomly at the same time; therefore, electronic noise (i.e., stochastic signals) are generated. As an advanced model, the electrophoretic effect in the SEPTIC sensor is discussed. In the viral sensor, since the combination of the analyte and a specific receptor located at the surface of the silicon nanowire occurs randomly in space and time, a stochastic signal is obtained. A mathematical model for a pH silicon nanowire nanosensor is developed and the size quantization effect in the nanosensor is also discussed. The calculation results are in excellent agreement with the experimental results in the literature.
2

Thermodynamics and Kinetics of Nucleation and Growth of Silicon Nanowires

Shakthivel, Dhayalan January 2014 (has links) (PDF)
Si nanowires have potential applications in a variety of technologies such as micro and nanoelectronics, sensors, electrodes and photovoltaic applications due to their size and specific surface area. Au particle-assisted vapour-liquid-solid or VLS growth method remains the dominant process for Si nanowire growth. A comprehensive kinetic model that addresses all experimental observations and provides a physico-chemical model of the VLS growth method is thus essential. The work done as part of this research is divided into two sections. A steady state kinetic model was first developed for the steady state growth rate of Si nanowires using SiCl4 and SiH4 as precursors. The steady state refers to a balance between the rates of injection and ejection of Si into the Au droplet. This balance results in a steady state supersaturation under which wire growth proceeds. In particular evaporation and reverse reaction of Si from the Au droplet and modes of crystal growth for wire growth have been considered in detail for the first time. The model is able to account for both, the radius independent and radius dependent growth rates reported in the literature. It also shows that the radius dependence previously attributed to purely thermodynamic considerations could also as well be explained just by steady state kinetics alone. Expressions have been derived for the steady state growth rate that require the desolvation energy, activation energy for precursor dissociation and supersaturation prevalent in the particle as inputs for calculation. In order to evaluate this model the incubation and growth of Si nanowires were studied on sapphire substrates in an indigenously built automated MOCVD reactor. Sapphire was chosen as the substrate, as opposed to Si which is commonly used, so as to ensure that the vapour phase is the only source of Si. A classical incubation period for nucleation, of the order of 4-8 minutes, was experimentally observed for the first time. Using the change in this incubation period with temperature a value of 15kT was determined to be the desolvation energy for growth using SiH4. The steady state growth rate of Si nanowires were measured and compared with the predictions of the model using the values of activation energies so determined. The thesis based on the current research work is organized as follows: Chapter 1 introduces the research area followed by a brief outline of the overall work Chapter 2 provides a summary of current literature, and puts the research described in this thesis in perspective. The diameter dependent growth rate of NWs which was initially solely attributed to the Gibbs-Thomson effect is first summarized. Experimental observations to the contrary are then highlighted. These contradictions provided the incentive for the research described in this thesis. Following a summary of the growth rate theories, the experimental observations on incubation available in the literature are summarized. All the other variants of the VLS method are also discussed. Chapter 3 describes the design, construction and working of an indigenously built semi- automated CVD reactor. This CVD reactor was used to conduct the Si NW growth experiments over sapphire substrates. Chapter 4 develops the physical chemistry model for Au catalyzed Si nanowire growth using SiCl4 and SiH4 precursors. The model originated from the contradictions present in the literature over the rate limiting step of the VLS growth mechanism and the steady state growth rate dependence on wire diameter. The development starts with explaining the thermodynamics of the steady state VLS process. The significance of the model lies in the detailed analysis of the all the atomistic process occurring during the VLS growth. In particular the evaporation and reverse reaction of Si from Au-Si droplet is explained in detail and possibly for the first time. Expressions for steady state growth rate by various modes, such as layer by layer growth (LL), by multilayer growth (ML) and growth by movement of a rough interface at the L-S growth interface are derived and presented. Chapter 5 discusses the results which emerge out the kinetic model from the previous chapter. Under a single framework of equations, the model is successful in explaining both the diameter independent and diameter dependent growth of NWs. As one of the major outcomes of the model, the growth rates of Si NWs are predicted and trends in growth rate are found to agree with those experimentally observed. Growth rate dependencies on pressure and temperature are implicitly included in the equations derived. An estimate of supersaturation has been extracted for the first time using the framework of equations. Chapter 6 contains the experimental results of the Si NW growth over sapphire substrates. An incubation period in the order of 3-8 minutes has been observed for Si NW growth on sapphire. The data has been compared with existing literature data and interpreted using classical transient nucleation theory. The incubation period data has been utilized to extract the kinetic parameter, QD, which is the desolvation enegy. These parameters and the measured steady state growth rates have been used to estimate the supersaturation existing in the droplet using the framework developed in chapters 4 and 5. Chapter 7 summarizes the outcome of the current research and highlights the future directions for the research problem addressed in this thesis.
3

Synthesis and Applications of Vertically Aligned Silicon Nanowire Arrays for Solar Energy Conversion

Yuan, Guangbi January 2012 (has links)
Thesis advisor: Dunwei Wang / Solar energy, the most abundant and free renewable energy, holds great promise for humanity's sustainable development. How to efficiently and inexpensively capture, covert solar energy and store it for off peak usages constitutes a grand challenge for the scientific community. Photovoltaic devices are promising candidates but are too costly to be implemented in large scales. On a fundamental level, this is due to the dilemma that the length scales of the optical pathways and electrical pathways often do not match within the photovoltaic device materials. Consider traditional Si solar cell as an example, effective light absorption requires up to hundreds of microns material while the photogenerated charge carries can only diffuse less than a few microns or even shorter before recombination. Such a problem may be solved by using Si nanowires (SiNWs) because vertically aligned nanowires can orthogonalize the light absorption and charge carrier collection pathways, thereby enabling the use of low-cost materials for practically appealing solar energy conversion devices. The objective of this thesis work is to explore low-cost synthesis of vertically aligned SiNW arrays and study their performance in both solar energy conversion and storage devices. We developed a method to synthesize vertically aligned SiNW arrays in a hot-wall chemical vapor deposition system with tunable length, doping level, and diameter for systematical studies. Empowered by the synthetic control, various types of vertical SiNW arrays were characterized by both steady-state (photoelectrochemical measurement) and transient (electrochemical impedance spectroscopy) techniques in a photoelectrochemical cell platform. Additionally, SiNWs were demonstrated to be a promising candidate for photoelectrochemical aromatic ketone reduction and CO₂ fixation. The reactions studied in this thesis are in close resemblance to natural photosynthesis and the resulted product molecules are precursors to nonsteroidal anti-inflammatory drugs, ibuprofen and naproxen. Lastly, vertical transparent conductive oxide nanotubes were prepared from vertical SiNW array templates. Ultrathin hematite (Fe₂O₃) film was coated on the nanotube scaffold by atomic layer deposition to form a heteronanostructure photoelectrode for efficient solar water oxidation. Our results highlight the potential of vertically aligned SiNW arrays in solar cell, solar water splitting and artificial photosynthesis applications. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
4

Silicon Nanowires for Integrated Photonics: Bridging Nano and Micro Photonics

Khorasaninejad, Mohammadreza January 2012 (has links)
Silicon Nanowires (SiNWs) with ability to confine carriers and photons in two directions while allowing propagation in third dimension offer interesting modified optical properties such as increased material absorption and optical non-linearities with regard to that of bulk silicon. Enhanced optical properties in SiNWs open a window not only to improve the performance of existing devices but also to realize novel structures. As such, I chose to investigate SiNWs for their applications in photonics, especially for sensing and non-linear devices. My goal was to conduct fundamental research on the optical properties of these SiNWs, and then develop an integration platform to realize practical devices. The platform should be compatible with IC manufacturing. Electron Beam Lithography (EBL) using a Poly Methyl Methacrylate (PMMA) resist followed by Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) is used for SiNWs fabrication. Now we are able to fabricate nanowires as small as 15 nm in diameter with the smallest separation of 50 nm. In addition, the interface between SiNWs and Si substrate is optically smooth enabling us to fundamentally understand optical properties of these structures. During the course of this project, I have contributed new fundamental knowledge about SiNWs. For example, Second Harmonic Generation (SHG) is demonstrated in SiNWs, which is absent in bulk silicon. This is achieved by self-straining the nanowires and is the first demonstration of this kind. Second-order non-linearities are more efficient for optical signal processing than third-order ones (which have been used for silicon photonics devices so far). Therefore, these results open a new area of research in silicon. In addition to second order nonlinearity, high enhancement of Raman scattering is achieved in SiNWs fabricated on Silicon on Insulator (SOI) substrate. This can find promising applications in sensing and nonlinear based devices such as optical switches and logic gates. Further, polarization resolved reflections from these nanowire arrays were measured and significant differences were observed for the reflection characteristics for the sand p-polarized beams. In order to understand these reflections, an effective index model is proposed based on calculations using Finite Difference Time Domain (FDTD) method. Results of this analysis provide useful information for designing of many optical devices using SiNWs such as solar cells and photodetectors. As another part of this thesis, vivid colors in mutually coupled SiNWs is demonstrated where nanowire diameters range from 105 nm to 345 nm. A simple sensor is demonstrated by observing the change in the reflected color with changing refractive index of the surrounding medium. A refractive index resolution of 5×10−5 is achieved using a simple charge coupled device (CCD) camera. Although, there were some paradigm shifting results during my fundamental studies, it became very apparent that SiNWs suffer from a major issue inhibiting their use in photonics devices. Below the diameter of 100 nm where these enhanced material properties were observed, SiNW is a poor optical waveguide with less than 1 % of light confined. The low confinement factor means that though the intrinsic properties of SiNWs increase, the overall device performance is not significantly enhanced. To overcome this issue, a new platform technology is invented, called Silicon Nanowire Optical Waveguide (SNOW). It combines the material advantages of nanostructures with the optical properties of conventional waveguides, and consists of arrays of nanowires in close proximity. It is shown that such a structure can guide an optical mode using the FDTD method. This waveguide structure can be used as a versatile platform to manufacture various devices such as sensors, switches, modulators, grating, and delay lines. For instance, a novel bio-sensor is proposed and designed whose sensitivity is enhanced by a factor of 20, compared to conventional silicon-wire waveguides.
5

Silicon Nanostructures For Electro-optical And Photovoltaic Applications

Kulakci, Mustafa 01 February 2012 (has links) (PDF)
Recently extensive efforts have been spent in order to achieve all silicon based photonic devices exploiting the efficient light emission from nanostructured silicon systems. In this thesis, silicon based nanostructures have been investigated for electro-optical and photovoltaic applications. The thesis focused on three application areas of silicon nanostructures: Light emitting diode (LED), light modulation using quantum confined Stark effect (QCSE) and photovoltaic applications. In the context of LED applications, ZnO nanocrystal/silicon heterojunctions were investigated. Contrary to observation of pure ultraviolet photoluminescence (PL) from ZnO nanocrystals that were synthesized through vapor liquid solidification (VLS) method, visible emissions were observed in the electroluminescence (EL) due to defect states of ZnO. The discrepancy between these emissions could be ascribed to both change in excitation mechanisms and the defect formation on ZnO nanocrystals surface during device fabrication steps. EL properties of silicon nanocrystals embedded in SiO2 matrix were also systematically studied with and without Tb doping. Turn-on voltage of the Tb doped LED structures was reduced below 10 V for the first time. Clear observation of QCSE has been demonstrated for the first time in Si nanocrystals embedded in SiO2 through systematic PL measurements under external electric field. Temperature and size dependence of QCSE measurements were consistently supported by our theoretical calculations using linear combination of bulk Bloch bands (LCBB) as the expansion basis. We have managed to modulate the exciton energy as high as 80 meV with field strength below MV/cm. Our study could be a starting point for fabrication of electro-optical modulators in futures for all silicon based photonic applications. In the last part of the thesis, formation kinetics of silicon nanowires arrays using a solution based novel technique called as metal assisted etching (MAE) has been systematically studied over large area silicon wafers. In parametric studies good control over nanowire formation was provided. Silicon nanowires were tested as an antireflective layer for industrial size solar cell applications. It was shown that with further improvements in surface passivation and contact formation, silicon nanowires could be utilized in very efficient silicon solar cells.
6

Aspects of bottom-up engineering : synthesis of silicon nanowires and Langmuir-Blodgett assembly of colloidal nanocrystals

Patel, Reken Niranjan 10 November 2010 (has links)
Central to the implementation of colloidal nanomaterials in commercial applications is the development of high throughput synthesis strategies for technologically relevant materials. Solution based synthesis approaches provide the controllability, high throughput, and scalability needed to meet commercial demand. A flow through supercritical fluid reactor was used to synthesize silicon nanowires in high yield with production rates of ~45 mg/hr. The high temperature and high pressure of the supercritical medium facilitated the decomposition of monophenylsilane and seeded growth of silicon nanowires by gold seeds. Crystalline nanowires with diameters of ~25 nm and lengths greater than 20 [micrometers] were routinely synthesized. Accumulation of nanowires in the reactor resulted in deposition of a conformal amorphous shell on the crystalline surface of the wire. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy were used to determine the shell composition. The shell was identified as polyphenylsilane formed by polymerization of the silicon precursor monophenylsilane. A post synthesis etch was developed to remove the shell while still maintaining the integrity of the crystalline silicon nanowire core. Subsequent surface passivation was achieved through thermal hydrosilylation with a terminal alkene. The development colloidal nanomaterials into commercial applications also requires simple and robust bottom-up assembly strategies to facilitate device fabrication. A Langmuir-Blodgett trough was used to assemble continuous monolayers of hexagonally ordered spherical nanocrystals over areas greater than 1 cm². Patterned monolayers and multilayers of FePt nanocrystals were printed onto substrates using pre-patterned polydimethylsiloxane (PDMS) stamps and a modified Langmuir Schaefer transfer technique. Patterned features, including micrometer-size circles, lines, and squares, could be printed using this approach. The magnetic properties of the printed nanocrystal films were also measured using magnetic force microscopy (MFM). Room temperature MFM could detect a remanent (permanent) magnetization from multilayers (>3 nanocrystals thick) films of chemically-ordered L1₀ FePt nanocrystals. Grazing incidence small angle X-ray scattering was used to quantitatively characterize the grain size, crystal structure, lattice disorder, and edge-to-edge spacing of the nanocrystal films prepared on the Langmuir-Blodgett trough both on the air-water interface and after transfer. / text
7

Silicon Nanowires for Integrated Photonics: Bridging Nano and Micro Photonics

Khorasaninejad, Mohammadreza January 2012 (has links)
Silicon Nanowires (SiNWs) with ability to confine carriers and photons in two directions while allowing propagation in third dimension offer interesting modified optical properties such as increased material absorption and optical non-linearities with regard to that of bulk silicon. Enhanced optical properties in SiNWs open a window not only to improve the performance of existing devices but also to realize novel structures. As such, I chose to investigate SiNWs for their applications in photonics, especially for sensing and non-linear devices. My goal was to conduct fundamental research on the optical properties of these SiNWs, and then develop an integration platform to realize practical devices. The platform should be compatible with IC manufacturing. Electron Beam Lithography (EBL) using a Poly Methyl Methacrylate (PMMA) resist followed by Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) is used for SiNWs fabrication. Now we are able to fabricate nanowires as small as 15 nm in diameter with the smallest separation of 50 nm. In addition, the interface between SiNWs and Si substrate is optically smooth enabling us to fundamentally understand optical properties of these structures. During the course of this project, I have contributed new fundamental knowledge about SiNWs. For example, Second Harmonic Generation (SHG) is demonstrated in SiNWs, which is absent in bulk silicon. This is achieved by self-straining the nanowires and is the first demonstration of this kind. Second-order non-linearities are more efficient for optical signal processing than third-order ones (which have been used for silicon photonics devices so far). Therefore, these results open a new area of research in silicon. In addition to second order nonlinearity, high enhancement of Raman scattering is achieved in SiNWs fabricated on Silicon on Insulator (SOI) substrate. This can find promising applications in sensing and nonlinear based devices such as optical switches and logic gates. Further, polarization resolved reflections from these nanowire arrays were measured and significant differences were observed for the reflection characteristics for the sand p-polarized beams. In order to understand these reflections, an effective index model is proposed based on calculations using Finite Difference Time Domain (FDTD) method. Results of this analysis provide useful information for designing of many optical devices using SiNWs such as solar cells and photodetectors. As another part of this thesis, vivid colors in mutually coupled SiNWs is demonstrated where nanowire diameters range from 105 nm to 345 nm. A simple sensor is demonstrated by observing the change in the reflected color with changing refractive index of the surrounding medium. A refractive index resolution of 5×10−5 is achieved using a simple charge coupled device (CCD) camera. Although, there were some paradigm shifting results during my fundamental studies, it became very apparent that SiNWs suffer from a major issue inhibiting their use in photonics devices. Below the diameter of 100 nm where these enhanced material properties were observed, SiNW is a poor optical waveguide with less than 1 % of light confined. The low confinement factor means that though the intrinsic properties of SiNWs increase, the overall device performance is not significantly enhanced. To overcome this issue, a new platform technology is invented, called Silicon Nanowire Optical Waveguide (SNOW). It combines the material advantages of nanostructures with the optical properties of conventional waveguides, and consists of arrays of nanowires in close proximity. It is shown that such a structure can guide an optical mode using the FDTD method. This waveguide structure can be used as a versatile platform to manufacture various devices such as sensors, switches, modulators, grating, and delay lines. For instance, a novel bio-sensor is proposed and designed whose sensitivity is enhanced by a factor of 20, compared to conventional silicon-wire waveguides.
8

Auto-assemblage générique de nanofils de silicium dans une matrice d'alumine nanoporeuse assisté par nanoimpression / Self-assembly silicon nanowires in nanoporous matrix of alumina obtained with nanoimprint process

Gorisse, Thérèse 28 March 2014 (has links)
Avec l'augmentation du nombre de dispositifs utilisant des nanostructures, tels les nanofils pour les systèmes photovoltaïques, les détecteurs, etc., il devient nécessaire de développer des techniques de fabrication de réseau d'objets de dimensions nanométrique à faible coût. Dans cette étude, nous utilisons les propriétés d'auto-assemblage combinées avec des méthodes « descendantes » pour créer des réseaux de nanostructures très denses et très organisés. En effet, nous proposons de produire des réseaux hexagonaux parfaits d'alumine poreuse (AAO) et de les utiliser pour la croissance confinée de fils de silicium (Si) par la technique de dépôt chimique en phase vapeur (CVD).L'AAO est naturellement obtenue par oxydation de l'aluminium dans un acide, mais ce processus seul n'apporte qu'une organisation des pores très faible. Nous présentons un procédé innovant utilisant la lithographie par nano-impression thermique pour pré-texturer l'aluminium avant son anodisation. Ainsi, nous obtenons des réseaux poreux hexagonaux parfait sur des surfaces allant jusqu'à 4 cm ². Toutes les caractéristiques géométriques de la membrane poreuse peuvent être ajustées en faisant varier les paramètres expérimentaux de l'anodisation. En outre, pour augmenter la densité du réseau et réduire le coût de fabrication du moule d'impression, nous avons développé des structures originales avec une croissance mixte de pores guidées et générer naturellement.Afin d'étudier les caractéristiques de ces réseaux et suivre leur évolution au cours de leur formation, nous présentons les résultats d'une étude de diffusion des rayons X aux petits angles réalisée in situ pendant la formation de l'AAO.L'AAO est finalement utilisée comme matrice guide pour la croissance auto-organisée de fils de Si par CVD. Nous présentons donc des réseaux hexagonaux parfaits de nanofils crus perpendiculairement à la direction <100 > des substrats de silicium. Les différentes étapes du procédé, du dépôt de catalyseur à la croissance des fils sont présentées. Grâce à cette technique, nous obtenons des densités de fils allant jusqu'à 9.109 cm-2 et la dispersion des diamètres est meilleure que lors d'une croissance colloïdale (CVD). La composition chimique et l'orientation cristalline des nanofils confirme qu'ils sont en silicium et que nous avons à la fois des orientations <100> et <111>. Nous avons étudié également la conductivité entre le sommet des fils et le substrat grâce à la technique du microscope à force atomique conducteur. / With the increased number of devices using functional nanostructures, e.g nanowires for photovoltaic systems, detector etc, it becomes of great importance to develop low-cost and versatile fabrication of systems with nano-objects. In this study, self-assembly properties combined with top-down methods were used to create highly dense and organized nanostructures. Indeed, flawless hexagonal porous anodic alumina arrays (PAA) were successfully used as a template for the epitaxial Silicon (Si) nanowires (NW) growth in a chemical vapor deposition reactor (CVD).PAA is naturally obtained by oxidation of aluminum in acid; however this simple process brings a poor pores organization. We present an innovative route using Thermal NanoImprint Lithography previous to aluminum anodization to prepare perfect hexagonal nanopore array on large surface (4 cm²). All the geometrical characteristics of the porous membrane can be adjusted by varying experimental parameters. Furthermore, to increase the density of the array and reduce the fabrication cost of the imprint mould, original structures with a mixed growth of NIL-guided pores and generation of naturally-guided pores (induced pores) have been developed. Shapes of the pores can be modified varying the electrolyte.To know the characteristic of these arrays and their evolution during formation, we will present the results of the hitherto unseen In Situ study under Grazing Incidence Small Angle X-ray Scattering of PAA formation.The PAA is finally used as templates for the self-organized Si NW growth in a CVD reactor. Hexagonal nanowire arrays grown perpendicularly to <100> silicon substrates were successfully produced. The different process steps from the catalyst deposition to the planarization of the array are presented. The quality of the final silicon array is discussed. Densities up to 9*109 NW.cm-2 and diameter dispersion better than colloidal growth are achieved. The chemical composition and the crystalline orientation of the nanowires confirms the nanowires are in silicon and a mix between <100> and <111> orientation. We also measured the conductivity between the top of the vertical nanowire and the substrate with conductive atomic force microscopy.
9

Multi-functional Hybrid Gating Silicon Nanowire Field-effect Transistors: From Optoelectronics to Neuromorphic Application

Baek, Eunhye 02 October 2020 (has links)
Enormous demands for fast and low-power computing and memory building blocks for consumer electronics, such as smartphones or tablets, have led to the emergence of silicon nanowire transistors a decade ago. Along with the Si-based nanotechnology, the silicon compatible optical and chemical sensing applications have boosted the research on hybrid devices that combine the organic and inorganic materials. Apart from the revolution in the device dimensions, the rapid growth of artificial intelligence in the software industry brunch requires the next generation’s computers with the revolutionized hybrid device architecture. Implementing such new devices can effectively perform machine learning tasks without the massive consumption of energy. The hybrid Si nanowire devices have an excellent capability to replace the conventional computing element by providing new functionalities of combined materials to the traditional transistor devices preserving the advantage of CMOS technology. A goal of this thesis is to develop functional hybrid Si nanowire-based transistors modulated by the stimuli-dependent gate to go beyond the current digital building blocks. The hybrid devices converge semiconductor channel and various materials from organic molecules to silicate composite as a gate of the transistor. External stimuli change the electronic state of the gate materials which is transformed to the gate potential of the transistors. First, this thesis studies the electronic characteristics of the Si nanowire FETs under the optical stimulus. Optical stimulus induces the strong conductance change on bare Si nanowire FETs. Under the light with low power intensity, the transistor shows an unconventional negative photoconductance (NPC) which is dependent on the doping concentration of the nanowire and the wavelength of the incident light. The dopants ions and surface states cause photo-generated hot electrons trapping which restricts conventional photoconductance in the semiconductor. In the hybrid device, however, the gate material on the Si dioxide layer plays a significant role in the optoelectronic modulation of the FET device. This thesis demonstrates that an organic photochromic material, porphyrin, wrapping around the nanowire channel acts as an optical gate of the Si nanowire transistor. The diffusive property of electrons in the molecular film decides the optical switching dynamics and efficiency. Further, this thesis introduces new functional gate material, sol-gel derived ion-doped silicate film, based on the availability of stimulus-dependent gate modulation. This amorphous and transparent silicate film shows memristive property due to the ionic redistribution in the film under bias condition. Interestingly, the sol-gel film-coated Si nanowire FETs the devices show a double gate effect cooperating with a back gate under light illumination which is due to the channel separation in the fin structure of the nanowire. In addition, the sol-gel silicate film-coated Si nanowire transistor emulates the neuronal plasticity with pulsed gate stimulation, namely “neurotransistor.” Because of the mobile ions in the silicate film, the transistor has a short-term memory and mimics membrane potential change of the neuron cell. The neurotransistor could be used as a computing node in the physical neural network for hardware machine learning. This work demonstrates that the physical properties of the gate material decide the transfer characteristics and time-dependent dynamics of the hybrid Si nanowire transistors. The optical and neuromorphic gate features of the hybrid transistors would accelerate the advancement of an optical or brain-like computing machine.
10

Fundamental Study on Carrier Transport in Si Nanowire MOSFETs with Smooth Nanowire Surfaces / 表面平坦化処理を施したSiナノワイヤMOSFETにおけるキャリヤ輸送の基礎研究

Morioka, Naoya 24 March 2014 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18286号 / 工博第3878号 / 新制||工||1595(附属図書館) / 31144 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 白石 誠司, 准教授 浅野 卓 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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