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Butt, Ali Muhammad. "New Photonic devices based on NLO(non-linear optical) crystalline waveguides." Doctoral thesis, Universitat Rovira i Virgili, 2015. http://hdl.handle.net/10803/403372.
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El RbTiOPO4 és un cristall de òptica no lineal amb alts coeficients electró-òptics i un llindar de dany òptic elevat, això el converteix en un material potencial per aplicacions electro-òptiques. Actualment hi ha un interès en el desenvolupament de components òptics basats en materials dielèctrics, identificat com un tema de recerca punter per Europa Horitzó 2020. La finalitat d’aquesta tesis és explorar el RTP com a plataforma dielèctrica per dispositius fotònics, que tenen aplicacions en les telecomunicacions i en el sensat biològic.
En aquesta tesis s’han crescut materials monocristal•lins en volum de RTP, K:RTP i Na:KTP pel mètode de Top seeded solution growth. Els cristalls obtinguts són òptims per ser utilitzats com a plataforma per fabricar guies d’ona i com a substrats pel creixement de capes epitaxials. Capes epitaxials de (Yb,Nb):RTP sobre RTP(001), RTP sobre K:RTP(001) i K.:RTP(100), i KTP sobre Na:KTP(001) s’han crescut per la metodologia de liquid phase epitaxy. Aquesta metodologia ha permès obtenir capes monocristal•lines amb una interfase d’alta qualitat cristal•lina
La fabricació de guies d’ona ha esta realitzada per RIE i ICP-RIE. Es reporta en aquesta tesis, un avanç en el coneixement del procés de etching del RTP. El mètode d’intercanvi iònic, amb Cs+ com ió, s’ha utilitzat per produir guies rectes, corbes i MZ. Degut a l’alta conductivitat iònica del RTP al llarg de la direcció c cristal•logràfica, l’ intercanvi iònic és altament factible i gairebé unidireccional.
S’ha obtingut exitosament el procés de guiat de llum en totes les guies d’ona fabricades. Pels Y-splitters i els MZ fabricats sobre els cristalls RTP/(Yb,Nb):RTP/RTP(001) estructurats amb RIE sobre la capa activa o bé el substrat, la guia obtinguda és monomode amb polarització TM a 1550 nm. Les pèrdues de propagació són de 3.5 dB/cm. Per les guies d’ona rectes fabricades sobre RTP/(Yb,Nb):RTP/RTP(001) per estructuració del recobriment per ICP-RIE, les pèrdues de propagació són 0.376 dB/cm a 1550 nm.El RbTiOPO4 es un cristal de óptica no-lineal con altos coeficientes electro ópticos y un límite de daño óptico elevado, eso lo convierte en una potencial material para aplicaciones electrópticas. Actualmente existe un gran interés en el desarrollo de componentes ópticos basados en materiales dieléctricos, esto ha sido identificado como un tema puntero de investigación por Europa Horizonte 2020. La finalidad de esta tesis es explorar el RTP cómo plataforma dieléctrica para dispositivos fotónicos, que tienen aplicaciones en les telecomunicaciones y en el sensado biológico. En esta tesis, se han crecido materiales monocristalinos en volumen de RTP, K:RTP y Na:KTP por el método de Top seeded solution growth. Los cristales crecidos son óptimos para ser utilizados como plataforma para fabricar guías de onda y como sustratos para el crecimiento de capas epitaxiales. Capas epitaxiales de (Yb,Nb):RTP sobre RTP(001), RTP sobre K:RTP(001) yK.:RTP(100), i KTP sobre Na:KTP(001) se han crecido mediante la metodología de liquid phase epitaxy. Esta metodología ha permitido obtener capes monocristalinas con una interfase de alta calidad cristalina. La fabricación de guías de onda se ha hecho por RIE y ICP-RIE: Se reporta en esta tesis un avance en el conocimiento del proceso de etching en el RTP. El método de intercambio iónico, con Cs+ como ion, se ha utilizado para producir guías de onda rectas, curvas y MZ. Debido a la alta conductividad iónica del RTP a lo largo de la dirección c cristalográfica, el intercambio iónico es altamente factible y casi unidireccional. Se ha obtenido el guiado con éxito en todas las guías de onda fabricadas. En los Y-Splitters y MZ fabricados sobre los cristales RTP/(Yb,Nb):RTP/RTP(001) estructurados con RIE sobre la capa activa o bien el sustrato, la guía obtenida es monomodo con la polarización TM a 1550 nm. Las pérdidas de propagación son de 3.5 dB/cm. Para las guías de onda rectes fabricadas sobre RTP/(Yb,Nb):RTP/RTP(001) por estructuración del recubrimiento por ICP-RIE, las pérdidas por propagación son de 0.376 dB/cm a 1550 nm.
RbTiOPO4 is a non-linear optical crystal with high electro-optic coefficients and high optical damage threshold, which makes it suitable for electro-optic applications. There’s a current interest in developing dielectric based photonic components for integrated optics, identified as a topic of research by the Europe Horizon 2020. The aim of this thesis is to explore RTP for dielectric based photonic platforms, which have applications in telecommunications and biosensing. In this thesis is reported the successful grow of bulk single crystals of RTP, K:RTP and Na:RTP by Top Seeded Solution Growth technique. The crystals obtained are suitable to be used as platforms to fabricate optical waveguides and for substrates for growth of epitaxial layers. Epitaxial layers of (Yb,Nb):RTP were grown on RTP(001), RTP was grown on K:RTP(001) and K:RTP(100) and KTP was grown on Na:KTP(001) by Liquid phase epitaxy. This methodology allows obtaining a single crystalline layer, with high quality crystalline interface. Waveguide fabrication was performed by RIE and ICP-RIE. Advancement in this etching process on RTP is reported in this thesis. Cs+ ion exchange method was used to produce straight, bends and MZ waveguides. Due to the RTP high ionic conductivity along the c crystallographic direction, ion exchange is highly feasible and almost unidirectional. Waveguiding of the fabricated channel waveguides has been successful. For the Y-Splitter and MZ waveguides fabricated on the RTP/(Yb,Nb):RTP/RTP(001) crystals, by structuring the active layer or the substrate by RIE, the waveguides obtained were single mode in TM polarization at 1550 nm. The propagation loss was 3.5 dB/cm. For straight waveguides fabricated on the RTP/(Yb,Nb):RTP/RTP(001), by structuring the cladding by ICP-RIE, the propagation losses were 0.376 dB/cm at 1550 nm. The waveguides fabricated by Cs+ ion exchange have larger losses due to inhomogeneity on the Cs exchange among different ferroelectric domains present in the structure.
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Wilkinson, Scott Tolbert. "Photonic devices for optical interconnects using epitaxial liftoff." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/15059.
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Herrera, Daniel. "Sulfur Implanted GaSb for Non-Epitaxial Photovoltaic Devices." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/93767.
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Gallium antimonide (GaSb) is a promising low-bandgap binary substrate for the fabrication of various infrared-based optoelectronic devices, particularly thermophotovoltaics (TPV). In order to make GaSb-based technologies like TPV more widely available, non-epitaxial dop- ing methods for GaSb must be pursued. Ion implantation is relatively unexplored for GaSb, and can offer advantages over the more common method of zinc diffusion, including higher flexibility with regards to substrate type and control over the resulting doping profile. Pre- vious work has shown beryllium (Be+) implantation to be a suitable method for fabricating a diode in an n-type GaSb substrate, opening the possibility for other ions to be considered for implanting into both n-type and p-type substrates.
This work identifies sulfur (S+) as another species to investigate for this purpose. To do so, material and electrical characterization was done on S+ and beryllium implanted GaSb films grown onto a semi-insulating gallium arsenide (GaAs) substrate. X-ray Diffraction spectroscopy (XRD) and Atomic Force Microscopy (AFM) indicate that the post-implant anneal of 600 for 10 s repaired the implant damage in the bulk material, but left behind a damaged surface layer composed of coalesced vacancies. While the beryllium implant resulted in moderate doping concentrations corresponding to an activation percentage near 15 %, Hall Effect data showed that implanting S+ ions induced a strongly p-type behavior, with hole concentrations above 1 × 19 cm^3 and sheet hole densities 3.5 times higher than the total implanted dose. This strong p-type behavior is attributed to the remaining lattice damage caused by the implant, which induces a large density of acceptor-like defect states near the valence band edge.
This technique was used on an unintentionally-doped p-type GaSb substrate to create a + /p junction. The implant process succeeded in producing a potential barrier similar to that of a hole-majority camel diode with a thin delta-doped region suitable for collecting diffused carriers from the p-type substrate. A post-fabrication etching process had the effect of strongly increasing the short circuit current density to as high as 41.8 mA/cm^2 and the open circuit voltage as high as 0.21 V by simultaneously removing a high carrier recombination surface layer. This etching process resulted in a broadband spectral response, giving internal quantum efficiencies greater than 90 %.Doctor of Philosophy
Thermophotovoltaics (TPV) is a technology that converts light and other forms of electromagnetic energy into electrical power, much like a typical solar panel. However, instead of sunlight, the energy source used in a TPV system is a terrestrial heat source at a temperature range of 1250–1750 ◦C, whose radiation is primarily infrared (IR). The IR-absorbing qualities and commercial availability of the compound semiconductor gallium antimonide (GaSb) have made it a key component in the development of absorber devices for TPV-related systems. GaSb-based devices have most often been fabricated using epitaxy, a method in which layer(s) of material are ‘grown’ in a layer-by-layer fashion atop a substrate GaSb wafer to induce an interface between negatively-charged (n-type) and positively-charged (p-type) regions. In order to improve upon the scalability of TPV production, device fabrication methods for GaSb that avoid the use of epitaxy are sought after as a lower-cost alternative. In this work, sulfur ion implantation is examined as one of these methods, in which elemental sulfur ions are injected at a high energy into a p-type GaSb substrate. The implanted ions then alter the charge characteristics at the surface of the material, producing an electric field from which a photovoltaic (PV) device can be fabricated. The results of this study showed that by implanting sulfur ions, an extremely p-type (p++) layer was formed at the surface of the GaSb substrate, which was attributed to residual damage induced by the implant process. The resulting interface between the p++ surface and the moderately p-type GaSb substrate was found to induce an electric field suitable for a PV device. Removing the excess surface damage away from the device’s metal contacts resulted in an improvement in the output electrical currents, with measured values being significantly higher than that of other devices made using more common non-epitaxial fabrication methods. The success of this work demonstrates the advantages of using a p-type GaSb substrate in place of an n-type substrate, and could help diversify the types of TPV-related devices that can be produced.
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Nagaredd, Venkata Karthik. "Fabrication, functionalisation and characterisation of epitaxial graphene devices." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2877.
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Graphene has attracted considerable attention in recent years due to its remarkable material properties and its potential for applications in next-generation nanoelectronics. In particular, the high specific surface area, extremely high electrical conductivity and exceptionally low electrical noise make graphene an ideal material for surface-sensitive applications such as chemical sensing, biological sensing and DNA sequencing. The surface cleanliness of graphene devices is critical for these applications, along with low contact resistance at metal/graphene interfaces. In addition, having pristine surface is also essential to carry out controlled functionalisation of graphene to target its chemical reactions with designated analyte species. However, it was found that conventional lithography processing techniques used for graphene device fabrication significantly contaminates the graphene surface with resist residues, which cannot be removed by any known organic solvents. The presence of such chemical contamination degrades the intrinsic properties of graphene and also significantly affects the performance of graphene based electronic devices. In this thesis, two methods were developed to address this issue, where, for the first method, rapid thermal annealing of graphene devices was performed in N2/H2 atmosphere, whilst for the second method, a metal sacrificial layer was used to prevent graphene from coming into direct with photoresist during the lithography process. Chemical, electrical, structural and surface morphological analysis showed that clean graphene surfaces can be achieved by both these methods, which allowed the intrinsic properties of graphene to be measured. In addition to surface contamination, the performance of graphene devices is also limited by contact resistance associated with the metal-graphene interface, where an unique challenge arise as charge carriers are injected from a three-dimensional metal film into a two-dimensional graphene sheet. The quantitative analysis of the data demonstrates that highly reactive metals such as Ti destroys the graphene lattice and results in high contact resistance, whereas metals with higher work functions and lower lattice mismatch to graphene (such as Ni) was found to result in significantly lower contact resistance. The work function, binding energy, diffusion energy and the lattice mismatch of the deposited metals were used to explain the electrical and structural characteristics of different types of metal/graphene interfaces. ABSTRACT vi In order to enhance the chemical reactivity of graphene surfaces, controlled functionalisation of epitaxial graphene films using electron-beam generated oxygen plasma has been demonstrated at room temperature. It was found that oxygen functionalisation not only introduces different oxygen functional groups onto the graphene surface, but also results in strain relaxation, in which the intrinsic compressive strain present in epitaxial graphene film decreased progressively with the increasing plasma pressure. A detailed study on the effect of e-beam plasma treatment on the chemical, electrical, structural and morphological characteristics of epitaxial graphene films have been investigated from initial to advanced oxidation stages. Finally, the effectiveness of oxygen functionalised graphene as a chemical sensor for detecting a wide range of polar chemical vapours in the ambient atmosphere has been demonstrated. The sensing characteristics of oxygen functionalised graphene devices showed ultra-fast response (10 s) and recovery times (100 s) to different chemical vapours, whilst unfunctionalised graphene sensors showed considerably weaker sensitivity and extremely slow recovery time in the range of ∼1.5 to 2 hours. A strong correlation between the dipole moment of the chemical and the magnitude of the response was observed, in which oxygen functionalised sensors displayed a twofold increase in the sensitivity over un-functionalised sensors with the increasing dipole moment from 2.0 D to 4.1 D. The sensing properties of graphene and the effect of oxygen functionalization on sensor responses were critically examined in an effort to provide a detailed understanding on the graphene sensing mechanism and provide a pathway for future advancements in the graphene sensor research.
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Turnbull, Aidan Gerard. "Relaxation in epitaxial layers of III-V compounds." Thesis, Durham University, 1992. http://etheses.dur.ac.uk/5709/.
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Semiconductor devices can be fabricated by growing III-V heteroepitaxial layers which are coherently strained to a III-V substrate. The relaxation of layer lattice strain through the nucleation of misfit dislocations near the interface causes a drop in performance for these devices. This thesis uses two non destructive x-ray techniques to examine relaxation in III-V epitaxial layers; double crystal diflractometry and x- ray topography. The dynamical and kinematical theories of x-ray diffraction are discussed in chapter 2. The apparatus used for double crystal diffractometry and x-ray topography and the theory of operation of these techniques is discussed in chapter 3. The properties of misfit dislocations in III-V epitaxial layers and the critical layer thickness at which relaxation occurs are discussed in chapter 4.Double crystal diffractometry and x-ray topography have been used to examine relaxation in epitaxial layers of AlAs on GaAs, InGaAs on GaAs, GaAsSb on GaAs, InGaAs on InP and an InGaAs superlattice on InP. All layers were deposited on 001 orientated substrates. Asymmetric double crystal rocking curves have been analysed using a novel technique which allows deduction of the position of an hhl layer reflection in reciprocal space. The layer unit cell parameters in the [110] and iTO] directions are determined from this. Individual misfit dislocation lines can be resolved by topography for dislocation line densities less than 0.2 μm(^-1)In each of these samples the layer relaxation was found to be asymmetric about the (110) directions. The sensitivity of diffractometry and topography to the detection of layer relaxation has been compared for samples with different thicknesses and dislocation line densities. The resolution of these techniques to the determination of layer relaxation has been shown to meet for a 1 μm layer of AlAs on GaAs. Tilt between the epitaxial layer lattice and the substrate has been measured for coherently strained and partially relaxed epitaxial layers grown on 001 orientated substrates. The lattice tilt in (110) directions was found to increase with misfit dislocation line density in these directions. Two theoretical models have been developed describing the relationship between lattice tilt and misfit dislocation line density and the tilts predicted by these compared with experiment. At high dislocation densities measurements of layer relaxation by diffractometry indicate that the images recorded by topography represent bundles of misfit dislocations and not individual dislocation fines. The number of dislocation lines per bundle was found to decrease with decreasing layer relaxation. Bunching of misfit dislocations into dislocation bundles is also observed on topographs from a low dislocation density sample where the individual dislocation hues are resolved. Screw dislocations in a strained layer and an interaction between two 60 dislocations to form a mixed dislocation have been characterised using Burgers vector analysis. Interference fringes have been observed on 004 double crystal rocking curves recorded from an ultra thin In GaAs layer sandwiched between a GaAs substrate and a GaAs cap. The position and intensity of these fringes was found to be sensitive to the composition and thickness of the In GaAs layer. Comparison between simulated and experimental rocking curve data allowed determination of the layer thickness to within a single monolayer and layer composition to within 0.5%. Topography of this sample showed that the dislocation line density varied from zero to 0.12 μm(^-1)across the wafer. The critical layer thickness and Indium concentration at which the first few misfit dislocation fines were observed was measured as 162 ± 2 A and 17 ± 0.5 %.
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Williams, Erica Jane. "Applications of epitaxial growth to semiconductor and superconductor devices." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239737.
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Li, Xuebin. "Epitaxial graphene films on SiC : growth, characterization, and devices /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24670.
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Thesis (Ph.D.)--Physics, Georgia Institute of Technology, 2008.Committee Chair: de Heer, Walter; Committee Member: Chou, Mei-Yin; Committee Member: First, Phillip; Committee Member: Meindl, James; Committee Member: Orlando, Thomas
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Hargis, Marian Crawford. "Metal-Semiconductor-Metal photodetectors and their integration via epitaxial liftoff." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/15800.
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ul, Hassan Jawad. "Epitaxial Growth and Characterization of SiC for High Power Devices." Doctoral thesis, Linköpings universitet, Halvledarmaterial, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-17440.
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Silicon Carbide (SiC) is a semiconductor with a set of superior properties, including wide bandgap, high thermal conductivity, high critical electric field and high electron mobility. This makes it an excellent material for unipolar and bipolar electronic device applications that can operate under high temperature and high power conditions. Despite major advancements in SiC bulk growth technology, during last decade, the crystalline quality of bulk grown material is still not good enough to be used as the active device structure. Also, doping of the material through high temperature diffusion is not possible while ion implantation leads to severe damage to the crystalline quality of the material. Therefore, to exploit the superior quality of the material, epitaxial growth is a preferred technology for the active layers in SiC-based devices. Horizontal Hot-wall chemical vapor deposition is probably the best way to produce high quality epitaxial layers where complete device structure with different doping type or concentrations can be grown during a single growth run. SiC exists in many different polytypes and to maintain the polytype stability during epitaxial growth, off-cut substrates are required to utilize step-flow growth. The major disadvantage of growth on off-cut substrates is the replication of basal plane dislocations from the substrate into the epilayer. These are known to be the main source of degradation of bipolar devices during forward current injection. The bipolar degradation is caused by expanding stacking faults which increases the resistance and leads to fatal damage to the device. Structural defects replicated from the substrate are also important for the formation of defects in the epitaxial layer. In this thesis we have developed an epitaxial growth process to reduce the basal plane dislocations and the bipolar degradation. We have further studied the properties of the epitaxial layer with a focus on morphological defects and structural defects in the epitaxial layer. The approach to avoid basal plane dislocation penetration from the substrate is to grow on nominally on-axis substrate. The main obstacle with on-axis growth is to avoid the formation of parasitic 3C polytype inclusions. The first results (Paper 1) on epitaxial growth on nominally on-axis Si-face substrates showed that the 3C inclusions nucleated at the beginning of the growth and expand laterally without following any particular crystallographic direction. Also, the extended defects in the substrate like micropipes, clusters of threading screw and edge dislocations do not give rise to 3C inclusion. The substrate surface damage was instead found to be the main source. To improve the starting surface different in-situ etching conditions were studied (Paper 2) and Si-rich conditions were found to effectively remove the substrate surface damages with lowest roughness and more importantly uniform distribution of steps on the surface. Therefore, in-situ etching under Si-rich conditions was performed before epitaxial growth. Using this 100 % 4H polytype was obtained in the epilayer on full 2” wafer (Paper 3) using an improved set of growth parameters with Si-rich conditions at the beginning of the growth. Simple PiN diodes were processed on the on-axis material, and tested for bipolar degradation. More than 70 % of these (Paper 4) showed a stable forward voltage drop during constant high current injection. High voltage power devices require thick epitaxial layers with low doping. In addition, the high current needs large area devices with a reduced number of defects. Growth and properties of thick epilayers have been studied in details (Paper 5) and the process parameters in Horizontal Hotwall chemical vapor deposition reactor are found to be stable during the growth of over 100 µm thick epilayers. An extensive study of epitaxial defect known as the carrot defect has been conducted to investigate the structure of the defect and its probable relation to the extended defects in the substrate (Paper 6). Other epitaxial defects observed and studied were different in-grown stacking faults which frequently occur in as-grown epilayers (Paper 7) and also play an important role in the device performance. Minority carrier lifetime is an important property especially for high power bipolar devices. The influence of structural defects on minority carrier lifetime has been studied (Paper 8) in several epilayers, using a unique high resolution photoluminescence decay mapping. The technique has shown the influence on carrier lifetime from different structural defects, and also revealed the presence of non-visible structural defects such as dislocations and stacking faults, normally not observed with standard techniques.Kiselkarbid (SiC) är en halvledare med överlägsna materialegenskaper, stort bandgap, hög termisk konduktivitet, hög kritisk fältstyrka och hög elektron mobilitet. Dessa gör den till ett utmärkt material för unipolära och bipolära komponenter som kan användas vid höga temperaturer, höga spänningar och höga strömmar. Trots stora framsteg under de senaste åren inom SiC bulk tillväxt, är material kvalitén hos bulk material fortfarande inte tillräckligt bra för att användas för aktiva skikt i komponenterna. Dessutom är dopning av materialet genom diffusion vid höga temperaturer inte möjligt, medan dopning via jonimplantation ger upphov till stora skador i kristallstrukturen. Därför behövs epitaxiell tillväxt av de aktive skikten i SiC baserade komponenter, för att fullt kunna utnyttja materialets egenskaper. Horisontell CVD (Hot-Wall Chemical Vapor Deposition) är en av de bästa tekniker att producera epitaxiella skikt med hög kvalité, där kompletta komponent strukturer med olika dopnings typ och koncentrationer kan växas i samma körning. SiC existerar i många polytyper och för att bibehålla polytype stabiliteten under tillväxt, används substrat med lutande kristallplan för använda s.k. step-flow tillväxt. En stor nackdel med substrat med lutande kristallplan är dock att dislokationer i basalplanet kommer att propagera från substratet in i det epitaxiella skiktet under tillväxten. Dessa dislokationer är den huvudsakliga orsaken till den degradering av bipolära komponenter som uppstår då höga strömmar går igenom komponenten. Den bipolära degraderingen orsakas av expanderade staplingsfel, som successivt ökar resistansen och slutligen förstörs komponenten. Strukturella defekter som replikeras från substratet är ofta även orsaken till kritiska defekter som skapas i det epitaxiella skiktet under tillväxt. I den här avhandlingen har vi utvecklat en epitaxiell som minskar problemet med basalplans dislokationer och bipolär degradering. Vi har även studerat egenskaper hos de epitaxiella skikten med fokus på morfologiska och strukturella defekter. Tekniken att hindra dislokationerna att replikeras in i de epitaxiella skikten bygger på att använda substrat utan lutning hos kristallplanen, s.k. on-axis substrat. Det hittills stora problemet med att växa på on-axis substrat har varit svårigheterna att bibehålla polytyp stabiliteten och undvika framförallt 3C polytyp inklusioner. Första försöken (Papper 1) försöken att växa epitaxi på on-axis substrat på Si sidan visade att 3C inklusionerna alltid startade i början av tillväxten för att sedan sprida sig lateralt under den fortsatta tillväxten. Vi kunde också visa att strukturella defekter som mikropipor, eller kluster av skruv- eller kant- dislokationer inte orsakade 3C inklusionerna. Den dominerande orsaken till 3C inklusionerna var istället skador eller repor på substratets yta. För att förbättra ytan innan den epitaxiella tillväxten studerade vi olika in-situ etsningar av ytan (Papper 2), och vi fann att etsning under Si dominerande förhållanden effektivast tog bort de flesta skador på substratets yta och gav en yta med minst ojämnheter. Dessutom skapades en homogen fördelning av atomära steg på ytan, och denna förbehandling användes sedan inför den epitaxiella tillväxten. Genom att dessutom optimera tillväxt förhållandena i inledningen av tillväxten kunde vi till 100% bibehålla samma polytyp från substratet in i det epitaxiella skiktet för hela 2” substrat (Papper 3). Enkla bipolära PiN dioder tillverkades och testades med avseende på bipolär degradering och mer än 70% av dioderna (Papper 4) visade ett stabilt framspänningsfall vid höga strömtätheter. Kraftkomponenter för höga spänningar kräver tjocka epitaxiella skikt med låg dopning. Dessutom, för höga strömmar krävs komponenter med stor aktiv area där kravet på lägre defekt täthet blir allt viktigare. Vi har i detalj studerat tillväxt och egenskaper av tjocka skikt (Papper 5), och funnit att de flesta material egenskaperna är stabila vid tillväxt av över 100 mm tjocka skikt i vår horisontella CVD reaktor. Vi har även i detalj studerat uppkomst och egenskaper av en av de mest kritiska epitaxiella defekterna, dem s.k. moroten (Papper 6). Speciellt har vi studerat dess uppkomst i relation till strukturella defekter i substratet. Vi har även studerat ända epitaxiella defekter i form av olika typer av staplingsfel (Papper 7), som även dessa har stor inverkan på komponenter. Livstiden för minoritetsladdningsbärarna är en viktig egenskap hos speciellt bipolära komponenter. I (Papper 8) har vi studerat hur denna påverkas av strukturella defekter i de epitaxiella skikten. Vi har använt en unik mätmetod för att optiskt kunna mäta över hela skivor, med hög upplösning. Mätningarna har lyckats påvisa hur olika strukturella defekter påverkar livstiden, och även kunnat visa på förekomsten av defekter som inte har upptäckts med andra mätmetoder.
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Hållstedt, Julius. "Integration of epitaxial SiGe(C) layers in advanced CMOS devices /." Stockholm : Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4498.
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Hållstedt, Julius. "Integration of epitaxial SiGe(C) layers in advanced CMOS devices." Doctoral thesis, KTH, Mikroelektronik och tillämpad fysik, MAP, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4498.
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Heteroepitaxial SiGe(C) layers have attracted immense attention as a material for performance boost in state of the art electronic devices during recent years. Alloying silicon with germanium and carbon add exclusive opportunities for strain and bandgap engineering. This work presents details of epitaxial growth using chemical vapor deposition (CVD), material characterization and integration of SiGeC layers in MOS devices. Non-selective and selective epitaxial growth of Si1-x-yGexCy (0≤x≤0.30, 0≤y≤0.02) layers have been performed and optimized aimed for various metal oxide semiconductor field effect transistor (MOSFET) applications. A comprehensive experimental study was performed to investigate the growth of SiGeC layers. The incorporation of C into the SiGe matrix was shown to be strongly sensitive to the growth parameters. As a consequence, a much smaller epitaxial process window compared to SiGe epitaxy was obtained. Incorporation of high boron concentrations (up to 1×1021 atoms/cm3) in SiGe layers aimed for recessed and/or elevated source/drain (S/D) junctions in pMOSFETs was also studied. HCl was used as Si etchant in the CVD reactor to create the recesses which was followed (in a single run) by selective epitaxy of B-doped SiGe. The issue of pattern dependency behavior of selective epitaxial growth was studied in detail. It was shown that a complete removal of pattern dependency in selective SiGe growth using reduced pressure CVD is not likely. However, it was shown that the pattern dependency can be predicted since it is highly dependent on the local Si coverage of the substrate. The pattern dependency was most sensitive for Si coverage in the range 1-10%. In this range drastic changes in growth rate and composition was observed. The pattern dependency was explained by gas depletion inside the low velocity boundary layer. Ni silicide is commonly used to reduce access resistance in S/D and gate areas of MOSFET devices. Therefore, the effect of carbon and germanium on the formation of NiSiGe(C) was studied. An improved thermal stability of Ni silicide was obtained when C is present in the SiGe layer. Integration of SiGe(C) layers in various MOSFET devices was performed. In order to perform a relevant device research the dimensions of the investigated devices have to be in-line with the current technology nodes. A robust spacer gate technology was developed which enabled stable processing of transistors with gate lengths down to 45 nm. SiGe(C) channels in ultra thin body (UTB) silicon on insulator (SOI) MOSFETs, with excellent performance down to 100 nm gate length was demonstrated. The integration of C in the channel of a MOSFET is interesting for future generations of ultra scaled devices where issues such as short channel effects (SCE), temperature budget, dopant diffusion and mobility will be extremely critical. A clear performance enhancement was obtained for both SiGe and SiGeC channels, which point out the potential of SiGe or SiGeC materials for UTB SOI devices. Biaxially strained-Si (sSi) on SiGe virtual substrates (VS) as mobility boosters in nMOSFETs with gate length down to 80 nm was demonstrated. This concept was thoroughly investigated in terms of performance and leakage of the devices. In-situ doping of the relaxed SiGe was shown to be superior over implantation to suppress the junction leakage. A high channel doping could effectively suppress the source to drain leakage.QC 20100715
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Castaing, Ambroise. "An investigation of epitaxial graphene growth and devices for biosensor applications." Thesis, Swansea University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678418.
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Negoro, Yuki. "Ion implantation and embedded epitaxial growth for 4H-SiC power electronic devices." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144921.
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Fisher, Martin John. "Epitaxial growth and characterisation of heterojunction and homojunction LEDs with InAs active regions." Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268062.
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Yang, Tiebin. "Interfacial Engineering of Thin Single-Crystal Lead Halide Perovskites for High-Performance Optoelectronic Devices." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/28205.
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Metal halide perovskites have demonstrated great potential in energy and optoelectronic device applications, due to their excellent optoelectronic properties. Among all the forms of halide perovskites, single crystals have attracted increasing research interest because of their longer carrier diffusion length, larger charge carrier mobility, and superior stability. However, the practical applications for the bulk perovskite crystals have been limited because of their large thickness and the difficulty of integration. In this regard, searching for the approaches to develop the high-quality halide perovskite thin single crystals with integration compatibility is highly desired, which would further improve the performance of the related devices. Moreover, enabling the halide perovskite thin single crystals with tunable thicknesses and sizes can also promote the construction of the single-crystal halide perovskite heterostructures with well-defined interfaces, which would open up a new realm for the perovskite-based electronic or optoelectronic devices.
In this thesis, the main aims are to develop the facile solution-processed methods to grow the high-quality epitaxial halide perovskite thin single crystals or various mixed-dimensional single-crystal heterostructures and probe the effect of interfaces on the material properties and the related device performance. In particular, the interfacial engineering on the epitaxial thin single crystals and the mixed-dimensional lateral heterostructures further enable various electronic and optoelectronic devices with improved performance and stability. Meanwhile, the thesis also provides in-depth insights into the mechanisms of ion migration and ionic diffusion with the related perovskite systems. The involved work projects and the related findings highlight the great potential and feasibility of halide perovskite thin single crystals and heterostructures in widely-ranged electronic and optoelectronic device applications.
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Wagner, Brent K. "Molecular beam epitaxial growth of CdTe and HgCdTe for new infrared and optoelectronic devices." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/13701.
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Warnick, Sean C. (Sean Charles). "Feedback control of organometallic vapor-phase epitaxial growth of aluminum gallium arsenide devices." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11150.
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Shibahara, Kentaro. "EPITAXIAL GROWTH OF SiC BY CHEMICAL VAPOR DEPOSITION AND APPLICATION TO ELECTRONIC DEVICES." Kyoto University, 1988. http://hdl.handle.net/2433/162216.
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John, Soji. "UHVCVD growth of Si₁-x-yGexCy epitaxial materials and application in heterostructure MOS devices /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Danno, Katsunori. "Epitaxial growth of 4H-SiC and characterization of deep levels for bipolar power devices." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136192.
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Nakamura, Shunichi. "Control of Step Structures on Silicon Carbide Surfaces in Epitaxial Growth toward Electronic Devices." 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149454.
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Abid, Mohamed. "Design and epitaxial growth of vertical cavity surface-emitting lasers (VCSEL) emitting at ultraviolet wavelength." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47682.
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One of the key advances in photonic technology in recent decades was the development of a new type of diode lasers emitting in the visible and infrared region. These vertical cavity surface-emitting lasers (VCSELs) emerged from a laboratory curiosity in 1977 [13] to an object of industrial mass production [14] and are currently used in many applications. The applications include communication, printing, and absorption spectroscopy [15]. Their rise in credibility has largely been motivated by the rapid evolution of their performance, the more sweeping recognition of their compatibility with low-cost wafer-scale fabrication, and their possible formation into specific arrays with no change in the fabrication procedure.
Various applications such as advanced chemical sensors and high-density optical storage require coherent and small-size ultraviolet-emitting devices (below 400nm). Therefore, to extend the VCSEL emission to the ultraviolet (UV) region, intensive efforts have been made in the VCSEL technology. However, the achievement of such UV VCSEL is very challenging because of the various limitations and issues. The issues noticeably include the carrier injection, optical confinement, and highly reflective distributed Bragg reflectors (DBR) structures with a broad bandwidth operating in the UV region [16]. In this context, motivated by the reported large refractive index induced by boron incorporation [7], we propose to introduce the boron-based material systems (BAlGaN) as an innovative solution to address some of the encountered difficulties.
The objective of the proposed research is to investigate and optimize new wide-bandgap BAlGaN material systems and illustrate their incorporation into the building blocks of vertical cavity surface-emitting laser structures for operation in the UV spectral range (<400nm).
Toward this goal, we have focused our research activities in three main directions. The first direction is devoted to the simulation of DBRs reflectivity by taking into consideration the experimental refractive indexes. Once the materials needed in the different components of the VCSEL are well defined, the second direction lies in the achievement of growth conditions optimization and characterization of the new wide-bandgap BAlGaN material systems. The study has led to the structural and morphological quality improvement of (B,Al,Ga)N materials. Unique optical properties of the BGaN and BAlN materials were also demonstrated. Upon demonstrating the materials' promising optical characteristics, the final direction consists of the epitaxial growth and characterization of the highly reflective DBRs and active region of the UV VCSEL structure.
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Xu, Xiaofeng. "Piezoelectric coupling constant in epitaxial Mg-doped GaN and design of pentacene acoustic charge transfer devices." [Ames, Iowa : Iowa State University], 2007.
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Wierzbowska, Katarzyna Barbara. "Studies of electronic and sensing properties of epitaxial InP surfaces for applications in gas sensor devices." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2007. http://tel.archives-ouvertes.fr/tel-00926562.
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Cette thèse est consacrée à l'étude de la physico-chimie des structures électroniques et microélectroniques à base de phosphure d'indium (InP). Le contexte scientifique de cette étude est d'abord abordé dans une description de la pollution atmosphérique ainsi que de sa métrologie. Les propriétés physico-chimiques et électroniques de InP sont particulièrement détaillées. Les structures des capteurs de gaz en cours de développement pour cette application sont ensuite répertoriées. Les méthodes de caractérisation chimique (spectroscopie de surface XPS et Auger, microscopie à force atomique AFM) et électronique (Van der Pauw) ainsi que l'analyse théorique des propriétés électroniques des couches minces sont également présentées. Enfin, des mesures en laboratoire à température et concentration variables de NO2 proches de celles rencontrées dans une atmosphère urbaine sont présentées. Les résultats obtenus suite à l'analyse théorique et aux différentes expériences ont montré le rôle prédominant des oxydes natifs présents à la surface de InP sur les réponses des capteurs. Ces derniers interviennent également sur la stabilité de la réponse aux gaz, tout comme leurs propriétés physico-chimiques. Les résultats des caractérisations électroniques et chimiques corroborent les résultats des essais des capteurs et permettent une modélisation de l'action du gaz sur InP
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Lochner, Florian [Verfasser], and Laurens W. [Akademischer Betreuer] Molenkamp. "Epitaxial growth and characterization of NiMnSb layers for novel spintronic devices / Florian Lochner. Betreuer: Laurens W. Molenkamp." Würzburg : Universitätsbibliothek der Universität Würzburg, 2012. http://d-nb.info/1024851850/34.
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Cariou, Romain. "Epitaxial growth of Si(Ge) materials on Si and GaAs by low temperature PECVD: towards tandem devices." Palaiseau, Ecole polytechnique, 2014. https://theses.hal.science/tel-01113794/document.
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Cette thèse s'intéresse à la croissance épitaxiale de Si et SiGe à basse température (200°C) par dépôt chimique en phase vapeur assistée par plasma (PECVD), et à l'utilisation de ces matériaux cristallins dans les cellules solaires en couches minces. L'objectif était de mieux comprendre cette croissance inattendue et d'étudier le potentiel de ces matériaux pour les cellules simples et multijonctions. Nous avons d'abord démontré qu'il est possible d'effectuer, avec un réacteur PECVD standard, un nettoyage efficace de la surface du c-Si et de poursuivre par une croissance épitaxiale de couches de Si jusqu'à 8µm d'épaisseur. L'impact des paramètres du procédé tels que la dilution du SiH4 dans l'H2, l'énergie des ions ou encore la pression totale, sur la qualité des couches a été mis en évidence. Les propriétés électriques et structurelles des couches ont été analysées, et nous avons démontré une amélioration de la qualité cristalline avec l'épaisseur de la couche. La croissance épitaxiale de Ge et SiGe sur c-Si dans des conditions similaires a également été établie. Ensuite, par une séquence d'étapes à moins de 200°C, des hétérojonctions PIN sur substrats très dopés, avec une couche absorbante épitaxiée de 1-4µm ont été réalisées, atteignant 8. 8% de rendement (sans piégeage optique) et 80% de FF. Le remplacement du Si par du Si0:73Ge0:27 a permis un gain de 11% sur le Jsc. Le contrôle de l'interface wafer/épi et des contraintes permet de favoriser le décollement : des couches epi-Si de 1. 5µm/10cm^2 ont été reportées sur verre avec succés. Nous avons également analysé l'influence de nanostructures photoniques sur les propriétés des dispositifs. L'étude conjointe de la croissance, du transfert et du piégeage optique ouvre la voie aux cellules c-Si ultra-minces (<10µm) bas côut. Enffin, contrairement au scénario classique de dépôt des matériaux III-V sur Si, nous avons étudié l'hétéroépitaxie de Si sur III-V. Avec cette approche, une bonne qualité cristalline de Si déposé directement sur GaAs est obtenue grâce aux faibles contraintes thermiques et à l'absence de problèmes de polarité à l'interface. Nous avons fabriqué des cellules GaAs avec 20% d'efficacité et des jonctions tunnel atteignant 55A/cm^2 par dépôt MOVPE. Une augmentation du courant tunnel par exposition au plasma d'hydrogène a aussi été démontrée. Ces résultats de croissance, cellule et jonction tunnel, couplés aux techniques de report, valident les briques élémentaires pour atteindre une cellule tandem AlGaAs(MOVPE)/SiGe(PECVD) à haut rendementThis thesis focuses on epitaxial growth of Si and SiGe at low temperature (200°C) by Plasma Enhanced Chemical Vapor Deposition (PECVD), and its application in thin film crystalline solar cells. Our goal is to gain insight into this unusual growth process, as well as to investigate the potential of such low temperaturedeposited material for single and multi-junction solar cells. First, we have proposed a one pump-down plasma process to clean out-of-the-box c-Si wafer surface and grow epitaxial layers of up to 8µm thick, without ultra-high vacuum, in a standard RF-PECVD reactor. By exploring the experimental parameters space, the link between layer quality and important physical variables, such as silane dilution, ion energy, or deposition pressure, has been confirmed. Both material and electrical properties were analyzed, and we found that epitaxial quality improves with film thickness. Furthermore, we could bring evidence of SiGe and Ge epitaxial growth under similar conditions. Then, with the whole process steps <200°C, we have achieved PIN heterojunction solar cells on highly doped substrates with 1-4µm epitaxial absorber, reaching 8. 8% efficiency (without light trapping) and 80. 5% FF. Replacing Si absorber by epitaxial Si0:73Ge0:27 resulted in 11% boost in Jsc. The use of an engineered wafer/epitaxial layer interface and stress enables easy lift-off: e. G. We successfully bonded 1. 5µm thick 10cm^2 epi-Si to glass. Additionally, we have considered the impact of photonic nanostructures on device properties. Together, the control of growth, transfer and advanced light trapping are paving the way toward highly efficient, ultrathin (<10µm) and low cost c-Si cells. Finally, in contrast with general trend of growing III-V semiconductors on Si, we have studied the hetero-epitaxial growth of Si on III-V. Good crystal quality was achieved by direct Si deposition on GaAs, thanks to reduced thermal load and suppressed polarity issues in this approach. Using MOCVD, we could build GaAs cells with 20% efficiency and III-V tunnel junctions reaching 55A/cm^2. Tunneling improvement upon H-plasma exposure was shown. Those results, combined with III-V layer lift-off, validate milestones toward high efficiency tandem AlGaAs(MOVD)/SiGe(PECVD) metamorphic solar cells
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Crossley, Samuel. "Electrocaloric materials and devices." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/245063.
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The temperature and/or entropy of electrically polarisable materials can be altered by changing electric field E. Research into this electrocaloric (EC) effect has focussed on increasing the size of the EC effects, with the long-term aim of building a cooler with an EC material at its heart. Materials and experimental methods are briefly reviewed. A ‘resetting’ indirect route to isothermal entropy change ∆S for hysteretic first-order transitions is described. An indirect route to adiabatic temperature change ∆T, without the need for field-resolved heat capacity data, is also described. Three temperature controllers were built: a cryogenic probe for 77-420 K with ∼5 mK resolution, a high-temperature stage with vacuum enclosure for 295-700 K with ∼15 mK resolution, and a low-temperature stage for 120-400 K with electrical access via micropositioners. Automation enables dense datasets to be compiled. Single crystals of inorganic salts (NH4)2SO4 , KNO3 and NaNO2 were obtained. Applying 380 kV cm−1 across (NH4)2SO4 , it was found that |∆S| ∼ 20 J K−1 kg−1 and |∆T | ∼ 4 K, using the indirect method near the Curie temperature TC = 223 K. Without the ‘resetting’ indirect method, |∆S| ∼ 45 J K−1 kg−1 would have been spuriously found. Preliminary indirect measurements on KNO3 and NaNO2 give |∆S| ∼ 75 J K−1 kg−1 for ∆E ∼ 31 kV cm−1 near TC = 400 K and |∆S| ∼ 14 J K−1 kg−1 for ∆E ∼ 15 kV cm−1 near TC = 435 K, respectively. A cation-ordered PbSc0.5Ta0.5O3 ceramic showing a nominally first-order transition at 295 K was obtained. The Clausius-Clapeyron phase diagram is revealed via indirect measurements where |∆S| ∼ 3.25 J K−1 kg−1 and |∆T | ∼ 2 K, and direct measurements where |∆T | ∼ 2 K. Clamped samples show broadening of the field-induced transition. Epitaxial, ∼64 nm-thick SrTiO3 films were grown by pulsed laser deposition on NdGaO3 (001) substrates with a La0.67Sr0.33MnO3 bottom electrode. The indirect method gives |∆S| ∼ 8 J K−1 kg−1 and |∆T | ∼ 3.5 K near 180 K with |∆E| = 780 kV cm−1. Finite element modelling (FEM) was used to optimise the geometry of multilayered capacitors (MLCs) for EC cooling. Intrinsic cooling powers of 25.9 kW kg−1 are predicted for an optimised MLC based on PVDF-TrFE with Ag electrodes.
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Yoo, Dongwon. "Growth and Characterization of III-Nitrides Materials System for Photonic and Electronic Devices by Metalorganic Chemical Vapor Deposition." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16220.
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A wide variety of group III-Nitride-based photonic and electronic devices have opened a new era in the field of semiconductor research in the past ten years. The direct and large bandgap nature, intrinsic high carrier mobility, and the capability of forming heterostructures allow them to dominate photonic and electronic device market such as light emitters, photodiodes, or high-speed/high-power electronic devices. Avalanche photodiodes (APDs) based on group III-Nitrides materials are of interest due to potential capabilities for low dark current densities, high sensitivities and high optical gains in the ultraviolet (UV) spectral region. Wide-bandgap GaN-based APDs are excellent candidates for short-wavelength photodetectors because they have the capability for cut-off wavelengths in the UV spectral region (λ < 290 nm). These intrinsically solar-blind UV APDs will not require filters to operate in the solar-blind spectral regime of λ < 290 nm. For the growth of GaN-based heteroepitaxial layers on lattice-mismatched substrates, a high density of defects is usually introduced during the growth; thereby, causing a device failure by premature microplasma, which has been a major issue for GaN-based APDs. The extensive research on epitaxial growth and optimization of Alx Ga 1-x N (0 ≤ x ≤ 1) grown on low dislocation density native bulk III-N substrates have brought UV APDs into realization. GaN and AlGaN UV p-i-n APDs demonstrated first and record-high true avalanche gain of > 10,000 and 50, respectively. The large stable optical gains are attributed to the improved crystalline quality of epitaxial layers grown on low dislocation density bulk substrates. GaN p-i-n rectifiers have brought much research interest due to its superior physical properties. The AIN-free full-vertical GaN p-i-n rectifiers on n - type 6H-SiC substrates by employing a conducting AIGaN:Si buffer layer provides the advantages of the reduction of sidewall damage from plasma etching and lower forward resistance due to the reduction of current crowding at the bottom n -type layer. The AlGaN:Si nucleation layer was proven to provide excellent electrical properties while also acting as a good buffer role for subsequent GaN growth. The reverse breakdown voltage for a relatively thin 2.5 μm-thick i -region was found to be over -400V.
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Gerhard, Felicitas Irene Veronika [Verfasser], and Charles [Gutachter] Gould. "Controlling structural and magnetic properties of epitaxial NiMnSb for application in spin torque devices / Felicitas Irene Veronika Gerhard. Gutachter: Charles Gould." Würzburg : Universität Würzburg, 2015. http://d-nb.info/1103259741/34.
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Zhang, Yun. "Development of III-nitride bipolar devices: avalanche photodiodes, laser diodes, and double-heterojunction bipolar transistors." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42703.
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This dissertation describes the development of III-nitride (III-N) bipolar devices for optoelectronic and electronic applications. Research mainly involves device design, fabrication process development, and device characterization for Geiger-mode gallium nitride (GaN) deep-UV (DUV) p-i-n avalanche photodiodes (APDs), indium gallium nitride (InGaN)/GaN-based violet/blue laser diodes (LDs), and GaN/InGaN-based npn radio-frequency (RF) double-heterojunction bipolar transistors (DHBTs). All the epitaxial materials of these devices were grown in the Advanced Materials and Devices Group (AMDG) led by Prof. Russell D. Dupuis at the Georgia Institute of Technology using the metalorganic chemical vapor deposition (MOCVD) technique.
Geiger-mode GaN p-i-n APDs have important applications in DUV and UV single-photon detections. In the fabrication of GaN p-i-n APDs, the major technical challenge is the sidewall leakage current. To address this issue, two surface leakage reduction schemes have been developed: a wet-etching surface treatment technique to recover the dry-etching-induced surface damage, and a ledged structure to form a surface depletion layer to partially passivate the sidewall. The first Geiger-mode DUV GaN p-i-n APD on a free-standing (FS) c-plane GaN substrate has been demonstrated.
InGaN/GaN-based violet/blue/green LDs are the coherent light sources for high-density optical storage systems and the next-generation full-color LD display systems. The design of InGaN/GaN LDs has several challenges, such as the quantum-confined stark effect (QCSE), the efficiency droop issue, and the optical confinement design optimization. In this dissertation, a step-graded electron-blocking layer (EBL) is studied to address the efficiency droop issue. Enhanced internal quantum efficiency (ɳi) has been observed on 420-nm InGaN/GaN-based LDs. Moreover, an InGaN waveguide design is implemented, and the continuous-wave (CW)-mode operation on 460-nm InGaN/GaN-based LDs is achieved at room temperature (RT).
III-N HBTs are promising devices for the next-generation RF and power electronics because of their advantages of high breakdown voltages, high power handling capability, and high-temperature and harsh-environment operation stability. One of the major technical challenges to fabricate high-performance RF III-N HBTs is to suppress the base surface recombination current on the extrinsic base region. The wet-etching surface treatment has also been employed to lower the surface recombination current. As a result, a record small-signal current gain (hfe) > 100 is achieved on GaN/InGaN-based npn DHBTs on sapphire substrates. A cut-off frequency (fT) > 5.3 GHz and a maximum oscillation frequency (fmax) > 1.3 GHz are also demonstrated for the first time. Furthermore, A FS c-plane GaN substrate with low epitaxial defect density and good thermal dissipation ability is used for reduced base bulk recombination current. The hfe > 115, collector current density (JC) > 141 kA/cm², and power density > 3.05 MW/cm² are achieved at RT, which are all the highest values reported ever on III-N HBTs.
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Choi, Suk. "Growth and characterization of III-nitride materials for high efficiency optoelectronic devices by metalorganic chemical vapor deposition." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45823.
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Efficiency droop is a critical issue for the Group III-nitride based light-emitting diodes (LEDs) to be competitive in the general lighting application. Carrier spill-over have been suggested as an origin of the efficiency droop, and an InAlN electron-blocking layer (EBL) is suggested as a replacement of the conventional AlGaN EBL for improved performance of LED. Optimum growth condition of InAlN layer was developed, and high quality InAlN layer was grown by using metalorganic chemical vapor deposition (MOCVD). A LED structure employing an InAlN EBL was grown and its efficiency droop performance was compared with a LED with an AlGaN EBL. Characterization results suggested that the InAlN EBL delivers more effective electron blocking over AlGaN EBL. Hole-injection performance of the InAlN EBL was examined by growing and testing a series of LEDs with different InAlN EBL thickness. Analysis results by using extended quantum efficiency model shows that further improvement in the performance of LED requires better hole-injection performance of the InAlN EBL. Advanced EBL structures such as strain-engineered InAlN EBL and compositionally-graded InAlN EBLs for the delivery of higher hole-injection efficiency were also grown and tested.
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Wu, Zhi Yuan. "SiGe/Si heterojunctions : investigations and device applications." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263768.
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Cristiano, Filadelfo. "Extended defects in SiGe device structures formed by ion implantation." Thesis, University of Surrey, 1998. http://epubs.surrey.ac.uk/843871/.
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The use of SiGe/Si heterostructures in the fabrication of electronic devices results in an improvement of the device performances with respect to bulk silicon. Ion implantation has been proposed as one of the possible technologies to produce these structures and, thus, the aim of this work is to develop an ion beam technology to fabricate strained SiGe heterostructures. The formation of extended defects in SiGe alloy layers formed by high dose Ge+ ion implantation followed by Solid Phase Epitaxial Growth (SPEG) has been investigated by transmission electron microscopy. Rutherford backscattering spectroscopy has also been used to determine the chemical composition and the crystalline quality of the synthesised structures. In addition, X-ray diffraction has been used to evaluate the strain level in selected samples. Two different structures have been studied in this project. The first consisted of "all-implanted" layers, where the Ge+ implants were followed in some cases by additional implants of Si+ and/or C+ ions, prior to SPEG, to investigate methods to inhibit defect formation. The second was achieved by capping the ion beam synthesised SiGe alloy layer by the deposition of a thin film of silicon, in order to realise structures compatible with device dimensions. Single crystal device worthy SiGe alloy layers have been achieved by implantation of Ge+ ions at energies ranging from 70 keV to 400 keV, where the only extended defects observed are EOR defects at a depth correspondent to the a/c interface formed during the Ge+ implant. In some cases, "hairpin" dislocations have also been observed in the vicinity of the EOR defects and extending up to the surface. Both types of defects are annihilated after post-amorphisation with 500 keV Si+ and replaced with dislocation loops at a depth of about 1 fj,m. For each Ge+ implantation energy a critical value of the peak germanium concentration exists above which the structures relax through the formation of stacking faults or "hairpin" dislocations nucleated in the vicinity of the peak of the germanium concentration depth profile and extending up to the surface. A critical value of the elastic energy stored in the structures (~300 mJ/m2) has been determined above which ion beam synthesised SiGe alloys relax, independently of the implantation energy. This empirical approach has been found to successfully account for the results obtained in this work as well as in many other studies reported in the literature. "Hairpin" dislocations formed under different experimental conditions have been investigated by plan view TEM and have been found to have the same crystallographic orientation () and Burgers vector (b= a ). Their formation has been explained within a "strain relaxation model". For a regrowth temperature of 700° C, all samples investigated by XRD have been found to be almost fully strained, including samples containing relaxation-induced defects, indicating that, under these conditions, the energy transferred to the defects is very low. C+ co-implantation has been successfully used to reduce both relaxation-induced defects and EOR dislocation loops. It is noted that a mixed technology entailing both layer deposition and ion implantation to produce the Si/SiGe/Si device structures requires extra process steps to control surface contaminations, pre cleaning and/or native oxide formation, resulting in increased fabrication costs. In this work an " all-implanted" route to the synthesis of Si/SiGe/Si device structures is therefore described, which exploits all of the advantages given by ion implantation.
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Kimoto, Tsunenobu. "Step-Controlled Epitaxial Growth of α-Sic and Device Applications." Kyoto University, 1995. http://hdl.handle.net/2433/77823.
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Chen, Chia-Wei. "Low cost high efficiency screen printed solar cells on Cz and epitaxial silicon." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54968.
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The objective of this research is to achieve high-efficiency, low-cost, commercial-ready, screen-printed Silicon (Si) solar cells by reducing material costs and raising cell efficiencies. Two specific solutions to material cost reduction are implemented in this thesis. The first one is low to medium concentrator (2-20 suns) Si solar cells. By using some optics to concentrate sunlight, the same amount of output power can be achieved with cell area reduced by a factor equal to the concentration ratio. Since the cost of optics is less than the semiconductor material, electricity price from the concentrator photovoltaics (PV) system is therefore reduced. The second solution is the use of epitaxially grown Si (epi-Si) wafers. This epi-Si technology bypasses three costly process steps (the need for polycrystalline silicon feedstock, ingot growth, and wafer slicing) compared to the traditional Si wafer technology and therefore reduces the material cost by up to 50% in a finished PV module. In addition, high efficiency Si solar cells with reduced metal contact recombination are studied and modeled by implementation of passivated contacts composed of tunnel oxide, n+ polycrystalline Si and metal on top of n-type Si absorber to reduce the cost ($/Wp) of PV module.
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Bowers, Cynthia Thomason. "Transmission Electron Microscopy Analysis of Silicon-Doped Beta-Gallium Oxide Films Grown by Pulsed Laser Deposition." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1580120635333744.
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Sprinkle, Michael W. "Epitaxial graphene on silicon carbide: low-vacuum growth, characterization, and device fabrication." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34735.
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In the past several years, epitaxial graphene on silicon carbide has been transformed from an academic curiosity of social scientists to a leading candidate material to replace silicon in post-CMOS electronics. This has come with rapid development of growth technologies, improved understanding of epitaxial graphene on the polar faces of silicon carbide, and new device fabrication techniques. The contributions of this thesis include refinement and improved understanding of graphene growth on the silicon- and carbon-faces in the context of managed local silicon partial pressure, high-throughput epitaxial graphene thickness measurement and uniformity characterization by ellipsometry, observations of nearly ideal graphene band structures on rotationally stacked carbon-face multilayer epitaxial graphene, presentation of initial experiments on localized in situ chemical modification of epitaxial graphene for an alternate path to semiconducting behavior, and novel device fabrication methods to exploit the crystal structure of the silicon carbide substrate. The latter is a particularly exciting foray into three dimensional patterning of the substrate that may eliminate the critical problem of edge roughness in graphene nanoribbons.
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Koerperick, Edwin John. "High power mid-wave and long-wave infrared light emitting diodes: device growth and applications." Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/304.
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High brightness light emitting diodes based on the InAs/GaSb superlattice material system have been developed for use in mid-wave and long-wave infrared optoelectronic systems. By employing a multiple active region device configuration, high optical output has been demonstrated from devices in the 3-5μm and 7-12μm spectral bands. Mid-wave infrared optical output in excess of 0.95mW/sr has been observed from 120×120μm2 devices with peak emission at 3.8μm, and nearly 160μW/sr has been measured from devices of the same size operating at 8μm. Larger devices (1×1mm^2) with output as high as 8.5mW/sr and 1.6mW/sr have been demonstrated with mid-wave and long-wave devices, respectively, under quasi-DC bias conditions.
The high switching speed inherent to small area light emitting diodes as well as potentially high optical output make these devices appealing candidates to improve upon the current state-of-the-art in infrared projection technology. Simulation of thermal scenes with wide dynamic range and high frame rates is desirable for calibration of infrared detection systems. Suitable projectors eliminate the need for observation of a live scene for detector calibration, thereby reducing costs and increasing safety. Current technology supports apparent temperature generation of up to approximately 800 Kelvin with frame rates of hundreds of frames per second; strong desire exists to break these barriers.
Meeting the requirements of the aforementioned application requires development of the InAs/GaSb superlattice material system on multiple levels. Suppressing parasitic recombination channels via band structure engineering, improving carrier transport between active regions and confinement within active regions, reduction of defect-assisted recombination by optimizing device growth, and improving device fabrication and packaging are all routes requiring exploration. This work focuses on the latter two components of the optimization process, with emphasis on molecular beam epitaxial growth of high quality devices. Particular attention was paid to tailoring devices for thermal imaging applications and the design tradeoffs and limitations which impact that technology. Device performance and optimization success were gauged by electronic, optical, morphological, and structural characterization.
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Nguyen, Hieu. "Molecular beam epitaxial growth, characterization and device applications of III-Nitride nanowire heterostructures." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107905.
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Recently, group III-nitride nanowire heterostructures have been extensively investigated. Due to the effective lateral stress relaxation, such nanoscale heterostructures can be epitaxially grown on silicon or other foreign substrates and can exhibit drastically reduced dislocations and polarization fields, compared to their planar counterparts. This dissertation reports on the achievement of a new class of III-nitride nanoscale heterostructures, including InGaN/GaN dot-in-a-wires and nearly defect-free InN nanowires on a silicon platform. We have further developed a new generation of nanowire devices, including ultrahigh-efficiency full-color light emitting diodes (LEDs) and solar cells on a silicon platform.We have identified two major mechanisms, including poor hole transport and electron overflow, that severely limit the performance of GaN-based nanowire LEDs. With the incorporation of the special techniques of p-type modulation doping and AlGaN electron blocking layer in the dot-in-a-wire LED active region, we have demonstrated phosphor-free white-light LEDs that can exhibit, for the first time, internal quantum efficiency of > 50%, negligible efficiency droop up to ~ 2,000A/cm2, and extremely high stable emission characteristics at room temperature, which are ideally suited for future smart lighting and full-color display applications.We have also studied the epitaxial growth, fabrication and characterization of InN:Mg/i-InN/InN:Si nanowire axial structures on n-type Si(111) substrates and demonstrated the first InN nanowire solar cells. Under one-sun (AM 1.5G) illumination, the devices exhibit a short-circuit current density of ~ 14.4 mA/cm2, open circuit voltage of 0.14 V , fill factor of 34.0%, and energy conversion efficiency of 0.68%. This work opens up exciting possibilities for InGaN nanowire-based, full solar-spectrum third-generation solar cells.Récemment, les hétérostructures à base de nitride et de groupe III ont fait l'objet de recherches intensives. Grâce à la relaxation latérale effective du stress, de telles hétérostructures d'échelle nanométrique peuvent être déposés sur du Silicium ou d'autres substrats. Celles-ci démontrent une réduction dramatique des dislocations et des champs de polarisations comparativement à leurs contreparties planes. Cette dissertation rapporte l'accomplissement d'une nouvelle classe de matériau nanométrique, soit des hétérostructures III-nitride incluant InGaN/GaN point dans fils ainsi que des nanofils d'InN presque sans défauts sur du Silicium. De plus, nous avons développé une nouvelle génération de dispositifs à base de nanofils, incluant des diodes émettrices de lumière (LEDs) à efficacité ultra haute et spectre visible complet ainsi que des cellules solaires sur une gaufre de Silicium. Nous avons identifié 2 mécanismes majeurs, incluant le faible transport des trous et le surplus d'électrons, qui limitent sérieusement la performance des LEDs à base de nanofils de GaN. Avec l'ajout de certaines techniques spéciales de modulation de type p, et une couche bloquante d'électrons faite de AlGaN dans la région active de la LED point dans fil. Par ailleurs, nous avons démontré des LEDs blanche sans phosphore qui démontrent, pour la première fois, une efficacité quantique supérieure à 50% ainsi qu'une baisse d'efficacité négligeable jusqu'à ~ 2,000A/cm2 et des caractéristiques d'émissions très hautes et stables à température pièce. Celles-ci sont donc toutes désignées pour des applications d'illumination intelligentes et des écrans pleines couleurs. La croissance par épitaxie, la fabrication et la caractérisation des nanofils d'InN:Mg/i-InN/InN:Si axiaux sur des substrats de Si(111) de type n et démontré la première cellule solaire à base d'InN. Sous l'illumination d'un soleil (AM 1.5G), les dispositifs démontrent une densité de courant de ~ 14.4 mA/cm2 en court-circuit, un voltage de circuit ouvert de 0.14V, un facteur de remplissage de 34.0% et une efficacité de conversion d'énergie de 0.68%. Ce travail ouvre des portes excitantes pour des cellules solaires plein spectre de troisième génération à base de nanofils d'InGaN.
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Chang, Bertha Pi-Ju. "Deposition and planarization of epitaxial oxide thin films for high temperature superconducting device applications." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38087.
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Namkoong, Gon. "Molecular beam epitaxy grown III-nitride materials for high-power and high-temperture applications : impact of nucleation kinetics on material and device structure quality." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16426.
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Zhao, Songrui. "Molecular beam epitaxial growth, characterization, and nanophotonic device applications of InN nanowires on Si platform." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117217.
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Dislocation-free semiconductor nanowires are an extremely promising route towards compound semiconductor integration with silicon technology. However, precise control over nanowire doping, together with the surface charge properties, has remained a near-universal material challenge to date. In this regard, we have investigated the molecular beam epitaxial growth and the correlated surface electrical and optical properties of InN nanowires, a promising candidate for future ultrahigh-speed nanoscale electronic and photonic devices and systems, on Si platform.By dramatically improving the epitaxial growth process, intrinsic InN nanowires are achieved, for the first time, both within the bulk and on the non-polar InN surfaces. The near-surface Femi-level is measured to locate below the CBM, suggesting the absence of surface electron accumulation. Such intrinsic InN nanowires can possess an extremely low free carrier concentration of ~1e13 /cm3, as well as a close-to-theoretically-predicted electron mobility in the range of 8,000 to 12,000 cm2/V·s at room temperature. This result is in direct contrast to the universally observed 2DEG on the InN grown surfaces. Furthermore, the surface charge properties of InN nanowires, including the formation of 2DEG and the optical emission characteristics can be precisely tuned, for the first time, through the controlled n-type doping.More importantly, p-type doping into InN nanowires is also realized, for the first time. The presence of Mg-acceptors is clearly demonstrated by the PL spectra. Furthermore, p-type surface is observed from the XPS experiments, indicating the presence of free holes. Additionally, p-type conduction is directly measured by single nanowire field effect transistors.In the end of this thesis, InN nanowire p-i-n photodiodes are fabricated, with a light response up to the telecommunication wavelength range at low temperatures. This thesis work provides a vivid example, and paves the way for the rational “materials by design” development of silicon integrated InN-based device technology in the nanoscale.Les nanofils semi-conducteurs sans dislocations sont une voie très prometteuse vers l'intégration des semi-conducteurs composés avec la technologie silicium. Cependant, un contrôle précis de dopage des nanofils, ainsi que les propriétés de charge de surface, reste un défi universel à ce jour. À cet égard, nous avons étudié la croissance épitaxiale par faisceau moléculaire et les propriétés de surface corrélés électriques et optiques des nanofils de InN sur du substrat de silicium, qui ont émergé comme candidat prometteur pour l'avenir des dispositifs électroniques et photoniques à très haute vitesse et à échelle nanométriques.Pour la première fois, en améliorant le processus de croissance épitaxiale, InN intrinsèque est atteint, à la fois dans le volume et sur les surfaces non polaires de InN. Le niveau de Fermi à la surface est mesuré et localisée sous le CBM, ce qui suggère l'absence d'accumulation d'électrons en surface. Ces nanofils InN intrinsèques possédent une concentration de porteurs libres très faible ~1e13 /cm3, ainsi que d'une mobilité proche de le théoriquement prédite d'électrons entre 8000 à 12000 cm2/V·s à température ambiante. Ce résultat est en contraste direct avec les 2DEG observés sur les surfaces d'InN. En outre, les propriétés de charge de surface de nanofils InN, y compris la formation de 2DEG et les caractéristiques d'émission optiques, peut être réglé avec précision, pour la première fois, par l'intermédiaire du contrôle d'incorporation de dopants de type n.Plus important encore, dopage de type p dans les nanofils InN est également réalisé pour la première fois. La présence de niveaux d'énergie Mg-accepteur est démontrée par les spectres de PL. Dans ces nanofils dopés de Mg, il n'y a pas d'accumulation d'électrons de surface et le niveau de Fermi dans le volume est proche de la VBM, ce qui indique un matériau de type p.En fin, la jonction p-i-n basé sur des nanofils InN photodétecteurs qui peut être utilisé en mode photovoltaïque est démontrée, avec une réponse à la lumière jusqu'à la longueur d'onde des télécommunications à de basses températures. Ce travail de thèse fournit un exemple frappant, ainsi que prépare le terrain pour le développement "matériaux par conception" de la technologie des dispositifs en silicium intégrée à base InN à l'échelle nanométrique.
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Xu, Cuiqin. "Optimisation du procédé de réalisation pour l'intégration séquentielle 3D des transistors CMOS FDSOI." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00771763.
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L'activation à basse température est prometteuse pour l'intégration 3D séquentielle où lebudget thermique du transistor supérieur est limité (<650 ºC) pour ne pas dégrader letransistor inférieur, mais aussi dans le cas d'une intégration planaire afin d'atteindre des EOTultra fines et de contrôler le travail de sortie de la grille sans recourir à une intégration de type" gate-last ". Dans ce travail, l'activation par recroissance en phase solide (SPER) a étéétudiée afin de réduire le budget thermique de l'activation des dopants.L'activation à basse température présente plusieurs inconvénients. Les travauxprécédents montrent que les fuites de jonctions sont plus importantes dans ces dispositifs.Ensuite, des fortes désactivations de dopants ont été observées. Troisièmement, la faiblediffusion des dopants rend difficile la connexion des jonctions source et drain avec le canal.Dans ce travail, il est montré que dans un transistor FDSOI, l'augmentation des fuites dejonctions et la désactivation du Bore peuvent être évités grâce à la présence de l'oxyde enterré.De plus les conditions d'implantation ont été optimisées et les transistors activés à650 ºC atteignent les performances des transistors de référence.
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Dubbelday, Wadad Brooke. "Residual strain and defects in solid phase epitaxial regrown Si and SiGe on sapphire and device applications /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9835373.
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FARAONE, GABRIELE. "Two-Dimensional Phosphorus: From the Synthesis Towards the Device Integration." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/304380.
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Gli allotropi bidimensionali (2D) del silicio e del fosforo sono stati i predecessori fra i materiali monoelementali 2D dopo il grafene. I vantaggi scientifici e tecnologici di questi materiali richiedono lo sviluppo di schemi di processo che possano garantire la loro effettiva integrazione in nuovi dispositivi per la nanoelettronica. In questo lavoro di tesi, sono stati investigati alcuni degli ostacoli ancora irrisolti lungo la strada per l’integrazione in dispositivo degli allotropi 2D del fosforo considerando specificatamente il caso delle fasi 2D α-P (corrispondente a un singolo strato di fosforo nero o fosforene) e \ β -P (fosforene-blu).
L’integrazione della fase 2D α-P nell’architettura di un dispositivo è stata oggetto di ampie ricerche e si basa su un percorso abbastanza consolidato che ha portato ad applicazioni che spaziano in un’ampia gamma di campi. Uno dei pochi ostacoli rimanenti su questo percorso è la mancanza di un metodo scalabile per produrre 2D α-P su grandi aree e con un accurato controllo dello spessore. In particolare, tale controllo è difficile da raggiungere nell’esfoliazione di cristalli stratificati di fosforo nero (BP). A questo proposito, la spettroscopia micro-Raman è stata usata sia come uno strumento metrologico per determinare lo spessore delle scaglie cristalline esfoliate che come metodo per raggiungere una controllata riduzione del loro spessore sfruttando la tecnica di assottigliamento laser. Tuttavia, i metodi di determinazione dello spessore basati sulla calibrazione delle intensità delle bande Raman sono stati investigati poco nel caso di scaglie cristalline multistrato. In questo lavoro di tesi abbiamo proposto un nuovo approccio basato sulla spettroscopia Raman che ha permesso di discriminare velocemente lo spessore di scaglie cristalline esfoliate di BP tra i 5 nm e i 100 nm. Inoltre, al fine di raggiungere un controllo migliore nel processo di assottigliamento laser, abbiamo anche investigato gli effetti dovuti al substrato sul riscaldamento e ablazione laser in scaglie multistrato di BP. Esperimenti di termometria Raman e calcoli numerici sul problema della diffusione del calore hanno chiarito che effetti ottici, termici e meccanici causati dalla presenza del substrato possono agire differentemente sul riscaldamento e sull’ablazione laser a seconda dello spessore delle scaglie cristalline.
Il percorso di integrazione in dispositivo per la fase 2D β -P, invece, è ancora assente a causa delle richieste più stringenti nella sintesi, basata su tecniche epitassiali, e dei problemi di instabilità fuori dall’ambiente di crescita in UHV. Questi ostacoli sono comunemente condivisi con gli altri membri della famiglia degli Xeni 2D e, in questo lavoro, sono stati studiati considerando il caso di β -P cresciuto epitassialmente su substrati di Au(111)/mica. I dettagli della sua struttura atomica e la reattività chimica all’esposizione in-situ ed ex-situ all’ossigeno sono stati analizzati con l’aiuto della microscopia a scansione ad effetto tunnel (STM) e spettroscopia fotoelettronica a raggi X (XPS). I problemi di instabilità in aria sono stati affrontati sviluppando una opportuna strategia di incapsulamento basata sulla crescita in-situ di un film protettivo di Al2O3 che, a sua volta, ha permesso di maneggiare il fosforo epitassiale lungo i primi passi di un processo di integrazione in dispositivo. Da questo punto di vista, sono stati esaminati due nuovi approcci per il trasferimento di un materiale epitassiale da un substrato di crescita verso substrati target. Ambedue questi metodi di trasferimento possono essere adeguatamente generalizzati all’intera classe degli Xeni epitassiali 2D cresciuti su metallo/mica. In particolare, l’universalità di questi approcci è stata impiegata per la fabbricazione di dispositivi FET e MIM sia su membrane di Al2O3/silicene multistrato/Ag(111) che su Al2O3/fosforo epitassiale/Au(111).Phosphorus and silicon two-dimensional (2D) allotropes have been the forerunners among the post-graphene monoelemental 2D materials. The scientific and technological advantages of these materials require the development of processing methods to guarantee their effective integration in new devices for nanoelectronics. In the present thesis work, some of the unresolved bottlenecks along the device integration path of 2D elemental phosphorus allotropes have been examined considering specifically the case of the α-P (single-layer black phosphorus or phosphorene) and β-P (blue phosphorene) 2D polymorphs. The integration of the 2D α-P phase in devices has been the subject of extensive investigations and nowadays relies on an almost consolidated path that has led to applications spanning a wide range of fields. One of the few remaining obstacles on this path is the lack of a scalable method to produce 2D α-P layers on large areas and with accurate control of the thickness. In particular, such control is difficult to achieve in the exfoliation of layered black phosphorus (BP) crystals. In this respect, micro-Raman spectroscopy has been used both as a metrological tool to determine the thickness of the exfoliated flakes and as method to achieve their controllable thickness reduction employing the laser thinning technique. However, thickness determination methods based on the calibration of the intensity of the Raman bands have been poorly investigated in the case of multilayer BP flakes due to difficulties caused by optical interferences and anisotropy effects. In this thesis work, we have proposed a novel Raman spectroscopy approach that, carefully accounting for these effects, allowed the quick discrimination of the thickness of exfoliated BP flakes between 5 nm and 100 nm. Moreover, in order to achieve a better control of the laser thinning process down to the ultimate 2D limit, we have also investigated the effects of the substrate on the laser heating and ablation of multilayer BP flakes. Raman thermometry experiments and numerical calculations of the heat diffusion problem have elucidated that optical, thermal, and mechanical effects caused by the substrate may act differently on the laser heating and ablation of the flakes depending on their thickness. An effective device integration route for the 2D β-P phase, instead, is still missing due to more stringent requirements in its synthesis, based on epitaxial techniques, and to the instability issue outside the UHV growth environment. These obstacles are commonly shared with other members of the family of 2D epitaxial Xenes and, in this work, have been investigated considering the case of β-P epitaxially grown on Au(111)/mica substrates. The details of its atomic structure and the chemical reactivity to ex-situ and in-situ oxygen exposure have been analyzed with the aid of Scanning Tunneling Microscopy (STM) and X-Ray Photoelectron Spectroscopy (XPS). The air-instability issues have been tackled by developing a suitable encapsulation strategy based on the in-situ growth of an Al2O3 capping layer that, in turn, allowed the handling of epitaxial phosphorus along the preliminary steps of a device integration process. In this respect, two novel approaches for the transfer of the epitaxial membrane from the growth substrate towards target substrates have been surveyed. Both the transfer methods can be suitably generalized to the whole class of 2D epitaxial Xenes grown on metal/mica paving the way for the establishment of methodological standards for their manipulation. In particular, the universality of such approaches has been exploited for the successful fabrication of back-gated FET and MIM devices on Al2O3/multilayer silicene/Ag(111) and Al2O3/epitaxial phosphorus/Au(111) mica-delaminated membranes, respectively. The epitaxial phosphorus MIM devices may open intriguing perspectives in the study of the non-volatile resistive switching in monoelemental epitaxial 2D materials.
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Ko, Tsung-Shine, and 柯宗憲. "Epitaxial growth of nonpolar GaN based optoelectronic devices." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/43011320137457312133.
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博士國立交通大學
光電工程系所
97
In this dissertation, the epitaxial growth of nonpolar a-plane GaN based optoelectronic materials grown using metal organic chemical vapor deposition (MOCVD) have been investigated. Main works include optimum growth, InGaN multiple quantum wells (MQWs) design, reduction of defects and the fabrication of a-plane GaN based optoelectronic devices and analysis of device characteristics. For optimum growth of a-plane GaN, we confirmed variation of thickness of AlN nucleation layer and V/III ratio of a-plane GaN growth influence crystal quality of a-plane GaN thin film. We also tried to figure out the mechanism of a-plane GaN by using Wulff plot and selective area growth to analyze the growth behavior of a-plane GaN grown on r-plane sapphire, which could be useful to explain the reasons account for stripes and pits exist on a-plane GaN surface and give us a guidance to predict growth of a-plane GaN. In this dissertation, we used trench epitaxial lateral over growth (TELOG) and InGaN/GaN supperlattices (SLs) to improve crystal quality of a-plane GaN. The threading dislocation (TD) density can be reduced largely from 1×1010 cm−2 to 3×107 cm−2 for the N-face GaN wing. As for SLs part, The TD density in the sample with SLs was reduced from 3×1010 cm-2 down to ~9×109 cm-2. For active layer structural design, a-plane InGaN/GaN MQWs of different width ranging from 3 nm to 12 nm have been grown. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 nm to 12 nm. Low temperature (9 K) time-resolved PL (TRPL) study shows that the sample with 3 nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. More effective capturing of excitons due to larger localization energy Eloc and shorter radiative lifetime of localized excitons are observed in thinner well width samples were observed in the temperature dependent PL and TRPL. In development of nonpolar light-emitting diodes (LEDs), we successfully fabricated a-plane LEDs structure by using TELOG GaN substrate. Due to there are two areas with different defect density in this kind sample, the emission wavelength will be changed when we increased injection current. The power was 0.2 mW at 140 mA injection current. On the other hand, we also fabricated nonpolar LEDs by using InGaN/GaN SLs layer. Electroluminescence intensity of the sample with InGaN/GaN SLs was enhanced by a factor of 3.42 times to that of the conventional sample without InGaN/GaN SLs. In this dissertation, we have achieved the studies on the growth of a-plane GaN and the fabrication of devices. Whole achievements include optimum growth, MQWs structural design, crystal improvement of material and fabrication of a-plane LEDs. We hope this series of experiments to provide a useful information and support for development of nonpolar optoelectronic devices in future.
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Jamil, Mustafa. "Germanium and epitaxial Ge:C devices for CMOS extension and beyond." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-08-3783.
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This work focuses on device design and process integration of high-performance Ge-based devices for CMOS applications and beyond. Here we addressed several key challenges towards Ge-based devices, such as, poor passivation, underperformance of nMOSFETs, and incompatibility of fragile Ge wafers for mass production. We simultaneously addressed the issues of bulk Ge and passivation for pMOSFETs, by fabricating Si-capped epitaxial Ge:C(C<0.5%) devices. Carbon improves the crystalline quality of the channel, while Si capping prevents GeOx formation, creates a quantum well for holes and thus improves mobility. Temperature-dependent characterization of these devices suggests that Si cap thickness needs to be optimized to ensure highest mobility. We developed a simple approach to grow GeO₂ by rapid thermal oxidation, which provides improved passivation, especially for nMOSFETs. The MOSCAPs with GeO₂ passivation show ~10× lower Dit (~8×10¹¹ cm⁻²eV⁻¹) than that of the HF-last devices. The Ge (111) nMOSFETs with GeO₂ passivation show ~2× enhancement in mobility (~715 cm²V⁻¹s⁻¹ at peak) and ~1.6× enhancement in drive current over control Si (100) devices. For improved n⁺/p junctions, we proposed a simple technique of rapid thermal diffusion from "spin-on-dopants" to avoid implantation damage during junction formation. These junctions show a high ION/IOFF ratio (~10⁵⁻⁶) and an ideality factor of ~1.03, indicating a low defect density, whereas, ion-implanted junctions show higher Ioff (by ~1-2 orders) and a larger ideality factor (~1.45). Diffusion-doped and GeO₂-passivated Ge(100) nMOSFETs show a high ION/IOFF ratio (~10⁴⁻⁵) , a low SS (111 mV/decade), and a high [mu]eff (679 cm²V⁻¹s⁻¹ at peak). Moreover, diffusion-doped Ge (111) nMOSFETs show even higher [mu]eff (970 cm²V⁻¹s⁻¹ at peak) that surpasses the universal Si mobility at low Eeff. For Beyond CMOS devices, we investigated Mn-doped Ge:C-on-Si (100), a novel Si-compatible ferromagnetic semiconductor. The investigation suggests that the magnetic properties of these films depend strongly on crystalline structure and Mn concentration. On a different approach, we developed LaOx/SiOx barrier for Spin-diodes that reduces contact resistance by ~10⁴, compared to Al₂O₃ controls and hence is more conducive for spin injection. These ferromagnetic materials and devices can potentially be useful for novel spintronic devices.text
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Lochner, Florian. "Epitaxial growth and characterization of NiMnSb layers for novel spintronic devices." Doctoral thesis, 2011. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-72276.
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In dieser Dissertation wurde das epitaktische Wachstum und die Charakterisierung des halb-metallischen Ferromagneten NiMnSb vorgestellt. NiMnSb kristallisiert in der C1b Kristallstruktur, welche ähnlich der Zinkblendestruktur von häufig verwendeten III-V Halbleitern ist. Eine besondere Eigenschaft von NiMnSb ist die theoretische 100% Spin-polarisation an der Fermikante, die es zu einem perfekten Kandidaten für Spintronikexperimente macht. Eine weitere große Rolle für diese Arbeit spielten die magnetischen Eigenschaften von NiMnSb, insbesondere die niedrige magnetische Dämpfung der abgeschiedenen Schichten. Alle gewachsenen Schichten wurden mit der MBE-Technik hergestellt. Die Schichtstapel für alle unterschiedlichen Experimente und Anwendungen wurden auf InP Substrate in (001) oder (111)B Orientierung abgeschieden. Vor der NiMnSb Schicht wurde eine undotierte (In,Ga)As Pufferschicht gewachsen. Für einige Proben auf InP(111)B wurde zusätzlich eine Si-dotierte (In,Ga)As-Schicht auf die undotierte (In,Ga)As-Schicht gewachsen. Die Dotierungskonzentration der n-dotierenten Schicht wurde per ETCH-CV bestimmt. Alle Schichten wurden auf strukturelle Eigenschaften und die NiMnSb-Schichten zusätzlich auf magnetische Eigenschaften untersucht. Für die strukturellen Untersuchungen wurde die in-situ Technik RHEED und das ex-situ Werkzeug HRXRD verwendet. Auf beiden Orientierungen zeigten die RHEED-Beobachtungen eine gute Qualität der gewachsenen Puffer- und halb-metallischen Ferromagnetschichten. Dieses Ergebnis wurde durch die HRXRD-Messung bestärkt. Es konnte die vertikale Gitterkonstante bestimmt werden. Der erhaltene Wert von NiMnSb auf InP(001) a(NiMnSb_vertikal) = 5.925 Å ist in guter Übereinstimmung mit dem Literaturwert a(NiMnSb_Lit) = 5.903 Å[Cas55]. Für NiMnSb auf InP(111)B wurde eine vertikale Gitterkonstante von a(NiMnSb_vertikal) = 6.017 Å bestimmt. Die horizontale Gitterkonstante des Puffers und des halb-metallischen Ferromagneten konnte in guter Übereinstimmung mit der Substratgitterkonstante bestimmt werden. Allerdings ist dieses Ergebnis ausschließlich bis zu einer Schichtdicke von ≈40nm für NiMnSb gültig. Um diese maximale Schichtdicke zu erhöhen, wurden NiMnSb auf InP(001) Substrate gewachsen und mit einer Ti/Au-Schicht als Schutz versehen. Mit diesen Proben wurden reziproke Gitterkarten des (533) Reflex mit GIXRD am Synchrotron BW2 des HASYLAB gemessen [Kum07]. Es hat sich gezeigt, dass sich die kritische Schichtdicke mehr als verdopppeln lässt, wenn eine Ti/Au- Schicht direkt nach dem Wachstum von NiMnSb abgeschieden wird, ohne das Ultrahochvakuum (UHV) zu verlassen. Die magnetischen Eigenschaften wurden mit FMR Experimenten und SQUID bestimmt. Der gemessene magnetische Dämpfungsparameter α einer 40nm dicken NiMnSb Schicht auf InP(001) wurde zu 3.19e−3 entlang [1-10] bestimmt. Die resultierende Linienbreite von unseren Schichten auf InP(001) ist mehr als 4.88 mal kleiner als bei [Hei04] gemessen. Ein weiteres Ergebnis ist die Richtungsabhängigkeit der Dämpfung. Es wurde gemessen, dass die Dämpfung sich um mehr als 42% ändert, wenn das angelegte Feld um 45° von [1-10] nach [100] gedreht wird. Mit SQUID messten wir die Sättigungsmagnetisierung von einer 40nm dicken NiMnSb-Schicht zu 4µB. NiMnSb-Schichten auf InP(111)B Substrate wurden ebenfalls mit FMR untersucht, mit einem überraschenden Ergebnis. Diese Schichten zeigten nicht nur eine Abnahme im Anisotropiefeld mit ansteigender Schichtdicke, sondern auch ein uniaxiales Anisotropieverhalten. Dieses Verhalten kann mit Defekten in diesen Proben erklärt werden. Mit einem Rasterkraftmikroskop (AFM) wurden dreieckige Defekte gemessen. Diese Defekte haben ihren Ursprung in der Pufferschicht und beeinflussen die magnetischen Eigenschaften. Ein weiterer Teil dieser Arbeit widmete sich dem Verhalten von NiMnSb bei Temperaturen um die 80K. In unserer Probe konnte ein Phasenübergang in den Messdaten des normalen Hall Koeffizienten, anomalen Hall-Term und Leitungswiderstand nicht beobachtet werden. Der letzte Teil dieser Arbeit behandelt verschiedene Spintronikanwendungen, welche aus unseren NiMnSb-Schichten gebaut wurden. In einer ersten Anwendung agiert die Magnetisierung auf einen Strom I. Die so genannte GMR-Anwendung besteht aus InP:S(001)- 180nm undotierten (In,Ga)As - 40nm NiMnSb - 10nm Cu - 6nm NiFe - 10nm Ru in CPP Geomtrie . Wir erhielten ein MR-Verhältnis von 3.4%. In einer zweiten Anwendung agiert der Strom I auf die Magnetisierung und nutzt dabei das Phänomen des Spin-Drehmomentes aus. Dieser so genannte Spin Torque Oscillator (STO) emittiert Frequenzen im GHz Bereich (13.94GHz - 14.1GHz). Die letzte hergestellte Anwendung basiert auf dem magnetischen Wirbelphänomen. Für das Umschalten der Kernpolarität sind die gyrotropischen Frequenzen f + = 254MHz, f − = 217MHz und ein totales, statisches magnetisches Feld von nur mµ0H = 65mT nötig. Die Umkehreffizienz wurde besser als 99% bestimmtIn this work the epitaxial growth and characterization of the half-metallic ferromagnet NiMnSb was presented. NiMnSb crystallizes in the C1b structure which is similar to the zinc blende structure from widely used III-V semiconductors. One special property of NiMnSb is the theoretical 100% spin-polarization at the Fermi edge. This makes it a perfect candidate for spintronic experiments and the material of choice for building novel spintronic devices. Another important topic in this work were the magnetic properties of NiMnSb, especially the low magnetic damping of the grown thin films. All grown layers were fabricated with the technique of MBE. The layer stacks for all different experiments and devices were grown on InP substrate in (001) or (111)B orientation. Before the NiMnSb layer a buffer layer of undoped (In,Ga)As was grown. Additional for some samples on InP(111)B, a Si doped (In,Ga)As layer was grown on top of the undoped (In,Ga)As layer. The dopant concentration of this n-doped layer was determined by ETCH-CV. All layers were investigated by structural and the NiMnSb layer additional by magnetic properties. For the structural investigation the in-situ technique RHEED and ex-situ tool HRXRD were used. RHEED observations showed a good quality of the grown buffer and half-metallic ferromagnet layers on both orientations. These results were strengthened by the HRXRD measurement. The vertical lattice constant could be determined. The received value of a(NiMnSb_vertical) = 5.925 Å for NiMnSb on InP(001) is in good agreement to the value a(NiMnSb_Lit) = 5.903 Å found in literature [Cas55]. For NiMnSb on InP(111)B a vertical lattice constant of a(NiMnSb_vertikal) = 6.017 Å could be determined. The horizontal lattice constant of the buffer and the half-metallic ferromagnet layer could be determined as the same of the substrate. For NiMnSb this conclusion is only valid up to a thickness of ≈40nm. To increase this maximum thickness, NiMnSb samples were grown on InP(001) substrates and capped with Ti/Au layers. Afterwards a reciprocal space map of the (533) reflex was drawn with GIXRD at the synchrotron beamline BW2 of HASYLAB [Kum07]. It has been shown that the critical thickness is more than doubled by depositing a Ti/Au capping directly after growth of NiMnSb without breaking the ultrahigh vacuum (UHV). The magnetic properties were determined with FMR experiments and SQUID measurements. The received magnetic damping parameter α from a 40nm thick NiMnSb layer on InP(001) could be determined to 3.19e−3 along [1-10]. The resulting line width of our NiMnSb layers on InP(001) is more than 4.88 times smaller than measured before [Hei04]. Another result is the direction dependence of the damping. It has been measured that the difference of the damping is changed by more than 42% when rotating the applied field by 45° from [1-10] to [100].With SQUID we measured a saturation magnetization of a 40nm thick NiMnSb layer as 4µB. NiMnSb layers on InP(111)B substrate where also measured with FMR with a surprising result. These layers not only showed a decreasing in the anisotropy field with increasing thickness but also an uniaxial anisotropy. This behaviour can be explained with defects on these samples. With an AFM triangle-like defects were measured. These defects originated from the buffer layer and influenced the magnetic properties. Another part of this work is dedicated to the behaviour of NiMnSb at temperatures around 80K. With our samples, no phase transition can be observed in the data of the Hall, anomalous Hall term and resistivity. The last part of this work discusses different spintronic devices build with our NiMnSb layers. In a first device the magnetization acts on the current. This Giant Magneto Resistance (GMR) device consisted of InP:S(001) - 180nm undoped (In,Ga)As - 40nm NiMnSb - 10nm Cu - 6nm NiFe - 10nm Ru in current perpendicular to plane (CPP) geometry. We received a Magneto-Resistance-Ratio of 3.4%. In a second device the current acts on the magnetization and makes use of the spin torque phenomena. This so called Spin Torque Oscillator (STO) emitted frequencies in the GHz range (13.94GHz - 14.1GHz). The last fabricated device is based on the magnetic vortex phenomena. For switching the core polarity the gyrotropic frequencies f + = 254MHz f − = 217MHz and a total static magnetic field of only mµ0H = 65mT were necessary. The reversal efficiency has been determined as better than 99% [Lou09]
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Huang, Huei-Min, and 黃煇閔. "Study of novel epitaxial structures for GaN-based light emitting devices." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/48851928881007778798.
Full textAbstract:
博士國立交通大學
光電工程學系
101
In the past, with the developments and requirements of the solid-state lighting, the study of the wide bandgap III-nitrides semiconductors recently become a popular investigated topic. However, unavoidable issues existed during the heteroepitaxial growth of III-nitrides semiconductors. Due to the lattice mismatch between the epilayers and substrate, the existence of high defect density resulted in the increase of non-radiactive recombination centers. Furthermore, the strain-induced polarization field and its effects conspicuously diminished the LED performance, leading to the poor light emitting efficiency. Therefore, the research attends to improving the light emitting efficiency by using the differnet epitaxial structures. First, the different epitaxial structure including the insertion of InGaN/GaN superlattices (SLS) layer and GaN homoepitaxial structures have been presented respectively, based on the defect reduction mechanism and the lattice matching epitaxy to improve the large lattice mismatch and high defect density. The inserted SLS layer and homoepitaxial growth structures indeed effectively reduce the threading dislocation density and the structural strain. Based on the internal quantum efficiency measurements, the inserted SLS-LED structure and the homoepitaxial growth LED structure reveal the 1.2-fold and 1.6-fold enhancement respectively. Subsequently, to eliminate the strain-induced polarization field effects, the wurtzite GaN-based quantum-confined structure are grown along the non-polar a-plane orientation direction by using metal-organic chemical vapor deposition. According to the experimental results, the interaction between the (11-20) quantum-confined structure and the (0001) basal stacking faults forms the quantum-wire-like structure to cause the strong carrier localization behavior. The light emitting efficiency exhibits the increase with the carrier localized energy, and thus it is inferred that that defect-induced carrier localization behavior could be helpful to enhance the light emitting efficiency in non-polar GaN-based nanostructure. Finally, we find that a distinctive hybrid structure which need neither the complex epitaxial growth nor the expensive substrate, can improve the light emitting efficiency. The hybrid strucutre consists of the InGaN/GaN multiple quantum wells (MQWs) and the graphene capping layer. In terms of the experimantal results, the polarization-free-like behavior, enhanced radiative recombination rate, reduced surface potential, and significant efficiency enhancement have been demonstrated. The internal quantum efficiency is effectively enhanced 2.0-fold, which is attributed with the large free carriers in the interface between GaN-based MQWs and graphene capping layer, leading to the screening of polarization field. In this thesis, the several effective approaches in order to enhance the light emitting efficiency have been proposed, and then expected the outcome of the research could contribute to the development and progress for GaN-based optoelectronic components.
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Li, Shu-Chu, and 李曙竹. "Fabrications and Characteristics of High Temperature Superconducting Bi-epitaxial Tunneling Devices." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/58223996265127538719.
Full textAbstract:
碩士國立臺灣大學
物理研究所
101
An bi-epitaxial technique for the fabrication of high temperature superconducting YBa2Cu3O7-δ (YBCO) artificial grain-boundary is researched. We have studied a bi-epitaxial structure, YBCO/CeO2/MgO and YBCO/MgO boundary. The CeO2 layers are grown on MgO substrates by using RF magnetron sputtering. Then, we define the grain boundary by optic lithography and ion-milling. YBCO films are grown by pulsed laser deposition (PLD). And try to add a SrTiO3 (STO) buffer layer to avoid the lattice mismatch between the pure YBCO film and the MgO substrate. The crystalline orientation and the surface morphology are characterized by X-ray diffraction and atomic force microscope (AFM). The electric and magnetic properties are also well studied by using low temperature measurement and superconducting quantum interference device (SQUID). The superconducting YBCO films reveal a high transition temperature Tc (R=0), and a critical current density in a zero magnetic field Jc which is large at 77 K. By measuring the characteristics of this device, and studying the properties of this superconducting thin film with grain-boundary, we find that this new structure can improve the artificial grain-boundary, and make device reveal very good properties with a high IcRn product, showing that this technique creates an opportunity to improve the fabrication of Josephson junction applications.