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Ciarkowski, Timothy A. "Low Impurity Content GaN Prepared via OMVPE for Use in Power Electronic Devices: Connection Between Growth Rate, Ammonia Flow, and Impurity Incorporation." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/94551.
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GaN has the potential to revolutionize the high power electronics industry, enabling high voltage applications and better power conversion efficiency due to its intrinsic material properties and newly available high purity bulk substrates. However, unintentional impurity incorporation needs to be reduced. This reduction can be accomplished by reducing the source of contamination and exploration of extreme growth conditions which reduce the incorporation of these contaminants. Newly available bulk substrates with low threading dislocations allow for better study of material properties, as opposed to material whose properties are dominated by structural and chemical defects. In addition, very thick films can be grown without cracking due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find growth conditions which reduces contamination without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of the intentional dopants.Doctor of Philosophy
GaN is a compound semiconductor which has the potential to revolutionize the high power electronics industry, enabling new applications and energy savings due to its inherent material properties. However, material quality and purity requires improvement. This improvement can be accomplished by reducing contamination and growing under extreme conditions. Newly available bulk substrates with low defects allow for better study of material properties. In addition, very thick films can be grown without cracking on these substrates due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find optimal growth conditions for high purity GaN without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of impurities.
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Ashourirad, Babak. "HETEROATOM-DOPED NANOPOROUS CARBONS: SYNTHESIS, CHARACTERIZATION AND APPLICATION TO GAS STORAGE AND SEPARATION." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/4062.
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Activated carbons as emerging classes of porous materials have gained tremendous attention because of their versatile applications such as gas storage/separations sorbents, oxygen reduction reaction (ORR) catalysts and supercapacitor electrodes. This diversity originates from fascinating features such as low-cost, lightweight, thermal, chemical and physical stability as well as adjustable textural properties. More interestingly, sole heteroatom or combinations of various elements can be doped into their framework to modify the surface chemistry. Among all dopants, nitrogen as the most frequently used element, induces basicity and charge delocalization into the carbon network and enhances selective adsorption of CO2. Transformation of a task-specific and single source precursor to heteroatom-doped carbon through a one-step activation process is considered a novel and efficient strategy.
With these considerations in mind, we developed multiple series of heteroatom doped porous carbons by using nitrogen containing carbon precursors. Benzimidazole-linked polymers (BILP-5), benzimidazole monomer (BI) and azo-linked polymers (ALP-6) were successfully transformed into heteroatom-doped carbons through chemical activation by potassium hydroxide. Alternative activation by zinc chloride and direct heating was also applied to ALP-6. The controlled activation/carbonization process afforded diverse textural properties, adjustable heteroatom doping levels and remarkable gas sorption properties. Nitrogen isotherms at 77 K revealed that micropores dominate the porous structure of carbons. The highest Brunauer-Emett-Teller (BET) surface area (4171 m2 g-1) and pore volume (2.3 cm3 g-1) were obtained for carbon synthesized by KOH activation of BI at 700 °C. In light of the synergistic effect of basic heteroatoms and fine micropores, all carbons exhibit remarkable gas capture and selectivity. Particularly, BI and BIPL-5 derived carbons feature unprecedented CO2 uptakes of 6.2 mmol g-1 (1 bar) and 2.1 mmol g-1 (0.15 bar) at 298 K, respectively. The ALP-6 derived carbons retained considerable amount of nitrogen dopants (up to 14.4 wt%) after heat treatment owing to the presence of more stable nitrogen-nitrogen bonds compared to nitrogen-carbon bonds in BILP-5 and BI precursors. Subsequently, the highest selectivity of 62 for CO2/N2 and 11 for CO2/CH4 were obtained at 298 K for a carbon prepared by KOH activation of ALP-6 at 500 °C.
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Kleinsorge, Britta Yvonne. "Doping of amorphous carbon." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621744.
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RIBEIRO, MARIO LUIS PIRES GONCALVES. "CARBON DOPING IN INAIAS EPITAXIAL LAYERS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2002. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=2651@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORERICSSON DO BRASIL
É reconhecido o potencial de usar carbono como um dopante tipo p em InAlAs devido a obtenção de elevados níveis de dopagem [1,2]. Entretanto, níveis elevados de dopagem só são alcançados em baixas temperaturas de crescimento (Tg inferiores a 600°C). Nessas temperaturas, as camadas crescidas apresentam qualidade ótica inferior quando comparadas com camadas crescidas em temperaturas mais altas, o que é prejudicial para dispositivos de optoeletrônica. Neste trabalho, é apresentada uma investigação sistemática das propriedades de transporte e óticas em camadas de InAlAs dopadas com carbono para diferentes temperaturas de crescimento. É observado que quanto mais baixa for a Tg maior será a incorporação de carbono e maior a atividade elétrica. Este resultado indica que o carbono é incorporado de diversas maneiras, bem como um aceitador raso. O carbono também pode ser incorporado como um doador raso, pois é um dopante anfotérico. Entretanto, este fato, não é suficiente para explicar os resultados de transporte. A diferença entre a concentração Hall e a concentração CV indica a incorporação de doadores profundos. Provavelmente, o carbono participa na formação desses doadores profundos, uma vez que a concentração de doador profundo varia linearmente com a densidade atômica de carbono, determinada pela técnica SIMS. Por outro lado, centros não radiativos são mais facilmente incorporados em baixas Tg e a eficiência da fotoluminescência é reduzida. Essa degradação da fotoluminescência é independente da concentração de carbono, consequentemente, pode-se concluir que essa redução na eficiência da fotoluminescência não está associada à presença de doadores profundos. Com a finalidade de obter um incremento na atividade elétrica do carbono e melhoria na qualidade ótica das camadas, as amostras foram submetidas a tratamentos térmicos. Os tratamentos térmicos aumentaram a concentração de buracos mas não influenciaram na densidade de doadores profundos ou na qualidade ótica das camadas. Para a utilização de InAlAs dopado com carbono em dispositivos, deve-se obter simultaneamente uma boa qualidade ótica e elevada atividade elétrica das camadas.Então, deve-se identificar o doador profundo, que está associado ao carbono, com o objetivo de reduzí-lo ou eliminá-lo e consequentemente, obter um incremento na atividade elétrica das camadas. Desta forma as camadas podem ser crescidas a temperaturas mais altas adequadas para uma emissão de fotoluminescência eficiente. Cálculos teóricos são apresentados de modo a ajudar essa identificação. Outra possibilidade é usar diferentes fontes de arsina em que as moléculas se dissociem em temperaturas mais baixas.
The potential of using carbon as a p-type dopant for InAlAs has already been recognized due to the achievable high hole concentration [1,2]. However, high doping levels are reached only for low growth teperatures (Tg below 600°C). These temperatures produce layers with poor optical quality as compared to those grown at higher temperatures, which can be detrimental for optoeletronic device. In this work we present crystal, transport and optical properties of such layers grown at different temperatures. We find that the lower Tg, the more efficient the carbon incorporation and its electrical activity are. This result indicates that carbon is incorporated in forms different from a shallow acceptor, as well. Carbon can also be incorporated as a shallow donor since it is an amphoteric dopant. However, this alone does not explain the transport results. The difference between the net free charge density determined from capacitance measurements indicates that a deep donor is also incorporated. Carbon most likely participates in the deep donor formation since the inferred deep donor concentration varies linearly with the carbon atomic density measured by SIMS. On the other hand, non- radiative deep levels are more efficiently incorporated as Tg is reduced degrading the photoluminescence characteristics. Such degration is independent of the carbon doping. Therefore, one concludes that the decrease in the photoluminescence efficiency cannot be related to the presence of the deep donor mentioned in the previous paragraph. To further probe the carbon electrical activity and its effect on the optical properties of the layers, the samples have been subjected to a heat-treatment. Annealing the samples increases the hole concentration, but neither affects the deep donor density nor improves the layers optical quality. In order to use carbon doped InAlAs in devices which simultaneously require good optical quality and high electrical activity of the layers, one should identify the deep donor involving carbon in order to try to reduce its concentration or even eliminate it, consequently improving the electrical activity of the layers. In such a way the layers can be grown at higher temperatures, adequate for an efficient photoluminescence emission. Theoretical calculations are being carried out to help with such identification. Another possibility is to use other arsine sources which crack at lower temperatures.
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Khromov, Sergey. "Doping effects on the structural and optical properties of GaN." Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-100760.
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Today there is a strong drive towards higher efficiency light emitters and devices for power electronics based on GaN and its ternary compounds. Device performance can be improved in several ways on the material level. Development of bulk GaN to substitute sapphire and SiC as substrate materials can allow lower defect density epitaxial GaN layers to be grown. Using nonpolar homoepitaxial layers alleviates the problem of polarization fields present in polar GaN epilayers. This thesis advances the field by attacking outstanding problems related to doping and its influence on structural and optical properties of GaN. Optical and structural investigations were performed on bulk GaN grown by halide vapor phase epitaxy (HVPE) and on polar and nonpolar epitaxial GaN grown by metal organic chemical vapor deposition (MOCVD), doped with different impurities: Mg, Si, O or C. Optical characterization was done using photoluminescence (PL), time-resolved photoluminescence (TRPL), and cathodoluminescence (CL) in-situ scanning electron microscope, whereas structural properties were studied by means of transmission electron microscopy (TEM) and atom probe tomography (APT). A correlation between Mg doping levels and stacking fault (SF) concentration in highly Mg-doped c-plane homoepitaxial GaN layers is found. Increasing Mg concentrations, from 2×1018 cm-3 to 5×1019 cm-3, coincides with increasing density of small, 3-10 nm-sized, SFs. Emission lines ascribed to SFs are observed in CL in all the studied samples. The observed SF-related luminescence can be explained by a model where Mg atoms interacting with the nearby SF changes the confinement for holes and leads to a pronounced defectrelated luminescence. Non-polar m-plane homoepitaxial GaN layers with Mg concentration of 2×1018 cm-3 and 3×1019 cm-3 exhibits high density of basal SFs as well as a number of prismatic SFs. Instead of normally observed in nonpolar GaN SF-related broad lines several sharp lines are detected in the 3.36-3.42 eV region. Their relation to donor-acceptor pair recombination (DAP) was dismissed by calculating the DAP energies and fitting with the measured spectra. The sharp lines are tentatively explained by some impurities bound to point defects or SFs. The origin of two Mg related acceptor bound exciton (ABE) peaks in the emission spectra is also proposed: narrower ABE1 peak at 3.466 eV is identified as coming from a substitutional Mg atom. Broader emission at 3.454 eV is deemed to be coming from a Mg acceptor atom perturbed by a nearby SF. Additionally, Mg cluster formation in the highest doped sample ([Mg] = 1×1020 cm-3) was revealed by APT. Simultaneous doping by Si and O was studied for HVPE grown bulk GaN. Doping with O concentration from 1017 cm-3 leads to a decrease in the Si concentration to less than 1016 cm-3. Si incorporation is believed to be suppressed by the competing Ga-vacancy-O incorporation process. Bandgap narrowing by 6 meV due to high doping was observed. Donor bound exciton (DBE) lifetime was obtained from TPRL experimental data and it is found to decrease with increasing doping. In non-polar m-plane homoepitaxial GaN Si doping influences the SF-related luminescence. At moderate Si concentrations excitons are bound to the impurity atoms or impurity-SF complex. Proximity of impurity atoms changes the potential for SF creating localization for charge carriers resulting in SF-related emission. At dopant concentrations higher than the Mott limit screening destroys the carrier interaction and, thus, the exciton localization at impurity-SF complex. Finally, C-doped HVPE grown bulk GaN layers were studied by TEM, CL, and TRPL. Enhanced yellow line (YL) luminescence was observed with increasing C doping. Stability of YL in a wide temperature range (5-300 K) confirms that YL is due to a deep defect, likely CN-ON complex. Low-temperature CL mapping reveals a pit-like structure with different luminescence properties in different areas. DBE emission dominates in CL spectra within the pits while in pit-free areas, in contrast, two ABE lines typical for Mg-doped GaN are observed.
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彭澤厚 and Chak-hau Pang. "A study of Mg doping in GaN during molecular beam epitaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31226619.
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Pang, Chak-hau. "A study of Mg doping in GaN during molecular beam epitaxy /." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25059075.
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Alluqmani, Saleh Marzoq B. "Growth and doping of carbon nanotubes and graphene." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/10949/.
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Single walled carbon nanotubes (SWCNTs) have been doped with nitrogen (N) by two ion-mediated approaches: directly through irradiation with N+ ions and by a novel indirect technique, creating defects through Ar+ ion irradiation which then react with nitrogen upon annealing in a N2 atmosphere. X-ray photoelectron spectroscopy (XPS) was then employed to determine the chemical environment of the nitrogen within the resulting SWCNT material. Depending upon the exact preparation conditions, nitrogen in graphitic (substitutional) pyridinic and pyrrolic configurations could be identified. Nitrogen doping through the novel method was found to introduce the largest concentration of chemisorbed nitrogen within the SWCNT films, dominated by thermodynamically unstable pyrrolic species at low process temperatures (500ºC). The maximum concentration of nitrogen in graphitic sites was achieved by direct ion bombardment, although both XPS and Raman spectroscopy indicated that this approach to doping led to the greatest damage. The ability to vary both bsolute and relative composition of chemisorbed nitrogen species is expected to be valuable for a range of fundamental studies, particularly of the catalytic behaviour of these materials. The growth of graphene on copper under atmospheric pressure using a soft solid source (nonadecane) is reported. It is found that the growth rate is best described by a model which involves the continuous supply of reactive species during the entire growth period. This observation is explained in terms of the formation of decomposition produces which reside on an otherwise clean surface after nonadecane desorption and provide a series of ‘mini carbon sources’ for graphene growth. XPS analysis indicates that, as expected, increased growth temperature leads to greater graphitisation at the surface (and hence graphene ‘quality’) which is not accompanied by any substantial change in island size and coverage. It is found that although graphene islands can be produced it is not possible to form continuous films, demonstrating the limitations of this technique. Although limited in some ways, the use of soft solid precursors for graphene growth allows the ready introduction of potential dopant materials. XPS, Raman and SEM data provide strong evidence that a PDMS precursor can be employed in atmospheric pressure solid-phase CVD to produce graphene heavily doped with silicon, which has not been previously achieved. Since silicon-doped graphene is predicted to possess a band gap related to the Si concentration, this may provide a route to produce a graphene-based material of use in digital electronics.
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Francis, Smita. "Optimisation of doping profiles for mm-wave GaAs and GaN gunn diodes." Thesis, Cape Peninsula University of Technology, 2017. http://hdl.handle.net/20.500.11838/2568.
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Thesis (DTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017.Gunn diodes play a prominent role in the development of low-cost and reliable solid-state oscillators for diverse applications, such as in the military, security, automotive and consumer electronics industries. The primary focus of the research presented here is the optimisation of GaAs and GaN Gunn diodes for mm-wave operations, through rigorous Monte Carlo particle simulations. A novel, empirical technique to determine the upper operational frequency limit of devices based on the transferred electron mechanism is presented. This method exploits the hysteresis of the dynamic velocity-field curves of semiconductors to establish the upper frequency limit of the transferred electron mechanism in bulk material that supports this mechanism. The method can be applied to any bulk material exhibiting negative differential resistance. The simulations show that the upper frequency limits of the fundamental mode of operation for GaAs Gunn diodes are between 80 GHz and 100 GHz, and for GaN Gunn diodes between 250 GHz and 300 GHz, depending on the operating conditions. These results, based on the simulated bulk material characteristics, are confirmed by the simulated mm-wave performance of the GaAs and GaN Gunn devices. GaAs diodes are shown to exhibit a fundamental frequency limit of 90 GHz, but with harmonic power available up to 186_GHz. Simulated GaN diodes are capable of generating appreciable output power at operational frequencies up to 250 GHz in the fundamental mode, with harmonic output power available up to 525 GHz. The research furthermore establishes optimised doping profiles for two-domain GaAs Gunn diodes and single- and two-domain GaN Gunn diodes. The relevant design parameters that have been optimised, are the dimensions and doping profile of the transit regions, the width of the doping notches and buffer region (for two-domain devices), and the bias voltage. In the case of GaAs diodes, hot electron injection has also been implemented to improve the efficiency and output power of the devices. Multi-domain operation has been explored for both GaAs and GaN devices and found to be an effective way of increasing the output power. However, it is the opinion of the author that a maximum number of two domains is feasible for both GaAs and GaN diodes due to the significant increase in thermal heating associated with an increase in the number of transit regions. It has also been found that increasing the doping concentration of the transit region exponentially over the last 25% towards the anode by a factor of 1.5 above the nominal doping level enhances the output power of the diodes.
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Khromov, Sergey. "The Effect of Mg Doping on Optical and Structural Properties of GaN." Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-75428.
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Mg is the most commonly used p-type dopant for GaN, however the impact of Mg incorporation on structural, morphological and optical properties of GaN is still not fully understood. Another research challenge is to understand and improve the properties of nonpolar GaN as it allows the fabrication of more efficient optoelectronic devices due to the absence of polarization fields. Thus, the aim of this thesis was to explore the effect of Mg doping on polar c-plane GaN in Paper 1 and nonpolar m-plane GaN in Paper 2. The samples were grown by metal-organic vapor phase epitaxy with varying Mg content on free-standing GaN substrates. The studies were done by transmission electron microscopy (TEM) and low temperature cathodoluminescence (CL) with the aim to correlate the optical and structural data obtained by these techniques. Polar c-plane GaN:Mg layers exhibit such structural defects as stackingfaults (SF) of a small size (5-10 nm). The basal plane SF (BSF)density was estimated to be ~ 105 − 106 cm−1 increasing with Mgconcentrations. Comparison between as-grown and annealed sampleshas not shown significant difference in structural or optical properties.Characteristic broad emission lines observed in CL in the rangeof 3.29 − 3.41 eV have been attributed to SF-related emissions byanalogy with nonpolar undoped GaN films grown heteroepitaxially.Acceptor bound exciton (ABE) emission and SF-related peaks havedemonstrated metastability. CL mapping performed on the TEMsamples at the energies corresponding to SF-related peaks has confirmedthat the origin of these lines is associated with Mg-doped GaNlayers. In nonpolar m-plane GaN:Mg layers similar BSFs have been observed. In addition more extended BSFs and prismatic SFs wereidentified at the interface with the GaN substrate. For the m-planesamples with Mg concentration of ~ 1019 cm−3 a number of fine CLlines have been detected in the region of 3.3-3.4 eV. Their shape andappearance were unlike the SF-related emissions in the case of c-planeGaN discussed in Paper 1. These peaks are not likely to be associatedwith donor-acceptor pair (DAP) recombination as has been proved byestimation of the separated DAP energies and by CL mapping experiment.A tentative explanation is given to these peaks as being relatedto excitons bound to some low symmetry acceptor defect centers.
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Fang, Zhihua. "N and p-type doping of GaN nanowires : from growth to electrical properties." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY007/document.
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Les nanostructures à base de nitrures d’éléments III suscitent un intérêt croissant, en raison de leurs propriétés singulières et de leurs applications technologiques potentielles, dans les diodes électroluminescentes (LED) notamment. La maîtrise et le contrôle du dopage de ces nanostructures est un enjeu crucial, mais difficile. A ce sujet, cette thèse apporte une contribution nouvelle, en explorant le processus de dopage de type n et p des nanofils (NFs) de GaN crus par épitaxie par jets moléculaires (EJM). En particulier, les propriétés électriques de ces structures ont été caractérisées par une approche multi-technique, à l’échelle du NF unique.Tout d'abord, les propriétés structurales et électriques d'une série de NFs de GaN dopés au Si (type n) ont été étudiées. Des mesures de spectroscopie de rayons X à haute résolution sur des NFs individuels ont mis en évidence une incorporation de Si plus élevée dans les NFs que dans les couches minces épitaxiées, ainsi qu’une migration du Si à la surface du NF pour le fil ayant le niveau de dopage le plus élevé. Des mesures de transport sur des NFs uniques (quatre contacts avec une température allant de 300 K jusqu’à 5 K) ont démontré un contrôle du dopage, avec une résistivité allant de 10^2 à 10^-3 Ω.cm et une concentration de porteurs comprise entre 10^17 et 10^20 cm-3. Des mesures réalisées sur des transistors à effet de champ à NFs uniques non intentionnellement dopés ont démontré qu’ils sont de type n avec une mobilité de porteurs élevée.Parallèlement à cela, les conditions de croissance de NFs de GaN dopés au Mg (p-type) et de jonctions p-n ont été déterminées afin d’obtenir une incorporation significative en Mg. Les propriétés électriques de jonctions p-n axiale à base de NFs de GaN posées sur un substrat de SiO2 et contactés avec de l’oxyde d’indium-étain (ITO) ont été étudiées en utilisant la technique du courant induit par faisceau électronique (EBIC). L’analyse EBIC a permis de localiser la jonction p-n le long du fil et de clairement montrer son bon fonctionnement en polarisation directe ou inverse. L'analyse EBIC a démontré que le GaN de type p est hautement résistif, confirmant ainsi les difficultés à réaliser des mesures de transport sur ce matériau.Cette étude originale a permis de décrire les propriétés électriques et de dopage de ces NFs de GaN à une échelle nanoscopique, facilitant ainsi la fabrication des futurs dispositifs incorporant des nanostructures à base de GaNIII-nitride nanostructures have been attracting increasing attention due to their peculiar properties and potential device applications as lighting LEDs. The control and evaluation of the doping in the nanostructures is a crucial, yet a challenging issue. This thesis advances the field by exploring the n and p type doping process of GaN nanowires (NWs) grown by molecular beam epitaxy (MBE). In particular, their electrical properties have been revealed through a multi-technique approach at the single NW level.Firstly, the structural and electrical properties of a series of Si-doped (n-type) GaN NWs have been studied. High resolution energy dispersive X-ray spectroscopy measurements on single NWs have illustrated the achievement of a higher Si incorporation in NWs than in epilayers, and Si segregation at the edge of the NW with the highest doping. Furthermore, direct transport measurements (four probes measurements from 300 K down to 5 K) on single NWs have shown a controlled doping with resistivity from 10^2 to 10^-3 Ω.cm, and a carrier concentration from 10^17 to 10^20 cm-3. Field effect transistor measurements have evidenced the n-type nature and a high electron mobility of the non-intentionally doped NWs.Secondly, the growth conditions of Mg-doped (p-type) and axial GaN p-n junction NWs have been determined to achieve significant Mg incorporation. Furthermore, the electrical properties of the axial GaN p-n junction NWs, dispersed on SiO2 and contacted by ITO, have been studied using electron beam induced current (EBIC) technique. EBIC technique revealed the location of the p-n junction and clearly demonstrated its operation under reverse and forward polarization. Moreover, EBIC showed highly resistive p-GaN in accordance with the difficulties to perform direct transport measurements on p-GaN NWs.This original study provides a nanoscale description of the electrical and doping properties of the GaN NWs, facilitating the fabrication of the future GaN nanostructures based devices
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Sanwick, Alexis. "Heteroatom-Doped Chemical Vapor Deposition Carbon Ultramicroelectrodes." Digital Commons @ East Tennessee State University, 2020. https://dc.etsu.edu/honors/592.
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Metal nanoparticles have been a primary focus in areas of catalysis and electrocatalysis applications as a result of their large surface area-to-volume ratios. While there is an increased interest in understanding the properties and behaviors of metal nanoparticles, they can become expensive over time. Recent research has incorporated the idea of using heteroatom-doped materials as a cheaper catalytic alternative to metal nanoparticles. In this study nitrogen-doping and phosphorous-doping techniques were applied to chemical vapor-deposited carbon ultramicroelectrodes in order to study the electrocatalytic properties toward the oxygen reduction reaction and the enhanced affinity for the deposition of gold nanoparticles onto the electrodes.
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Kendrick, Chito Edsel. "Revisiting Nitride Semiconductors: Epilayers, p-Type Doping and Nanowires." Thesis, University of Canterbury. Electrical and Computer Engineering, 2008. http://hdl.handle.net/10092/2108.
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This dissertation investigates the growth of high quality GaN and InN thin films by plasma assisted molecular beam epitaxy (PAMBE). It also explores the growth of self-seeded GaN branching nanowires and p-type doping of InN, two topics of particular interest at present.
The growth of high quality III-Nitride semiconductor thin films have been shown to be dependent on the group-III (metal) to nitrogen ratio. A metal-rich growth environment enhances the diffusion of the group-III adatoms through the formation of a group-III adlayer. By using a metal-rich growth environment, determined by growth rate studies using laser reflection interferometry or RHEED analysis of the surface, both GaN and InN films have been grown with a smooth surface morphology. Additionally the smooth surface morphology has beneficial effects on the electrical and optical properties of both materials. However, with the growth using a metal-rich environment, group-III droplets are present on all film surfaces, which can be an issue for device fabrication, as they produce facets in the crystal structure due to enhanced growth rates.
MBE growth of GaN nanowires via the vapour liquid solid (VLS) and vapour solid (VS) growth techniques have so far been based on the N-rich growth regime. However, we have shown that the Ga-rich growth regime can be used to grow self-seeded one dimensional and hierarchical GaN nanowires. 7 µm long hierarchical GaN nanowires with at least three branches were grown and shown to have a high crystalline quality. The suggested growth mechanism is a self-seeding VLS process driven by liquid phase epitaxy at the nanoscale, while the branching growth was nucleated due to the Ga-rich growth regime by excess Ga droplets forming on the trunk during growth. The growth of vertical GaN nanowires has also been achieved using the same self-seeding process and the critical parameter seems to be the Ga to N ratio. Also, the growth rate of the Ga-rich grown GaN nanowires can supersede the growth rates reported from N-rich grown GaN nanowires by at least a factor of two.
The fabrication of vertical and planar GaN nanowire devices has been demonstrated in this study. Two point and three point contacts were fabricated to the branching GaN nanowires in the planar direction with resistive measurements ranging from 200 - 900 kΩ, similar to chemical vapour deposition and MBE grown GaN nanowires. The nonlinear current-voltage characteristics from the three point contacts may lead to unique nano-devices. The planar nanowires have also shown to have potential as UV detectors. Schottky diodes were fabricated on the vertical nanowires, with values for the barrier heights consistent with bulk diodes.
Mg and Zn doping studies of InN were also performed. Both InN:Mg and InN:Zn have strong photoluminescence only at low doping concentrations. However, the InN:Mg films have reduced mobilities with increased Mg content, whereas the mobility determined from the InN:Zn films is independent of Zn. When the InN:Zn film quality was improved by growing under the In-rich growth regime, electrochemical capacitance-voltage results suggest n{type conductivity, and strong photoluminescence was obtained from all of the films with four features seen at 0.719 eV, 0.668 eV, 0.602 eV and 0.547 eV. The features at 0.719 eV and 0.668 eV are possibly due to a near band edge to valence band or shallow acceptor transition, while the 0.547 eV has an activation energy of 60 meV suggesting a deep level acceptor.
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Liang, Meng Suan. "Carbon doping in GaAs, AlGaAs, InGaAs and distributed Bragg reflectors." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399255.
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Anwar, Abdul Waheed. "Investigation of doping and photoexcitation in carbon nanotubes using Raman spectroscopy." Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1156/.
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La spectroscopie Raman est une technique de caractérisation non destructive appropriée pour l'étude des nanotubes des carbone. Des différences dans le décalage spectral des bandes Raman D et G, correspondant aux effets anharmoniques, sont observées lors d'un chauffage des nanotubes de carbone par irradiation photonique intense ou en faisant varier la température d'un thermostat. Les modifications spectrales du mode D sont attribués à des modifications du processus de double résonance Raman en raison de la variation de la structure de bande électronique provoquée par la creation des excitons. L'enquête de l'influence du dopage et de photoexcitation sur la bande G et la D de nanotubes de carbone montrent que la spectroscopie Raman peut être utilisé comme un outil de diagnostic. Les bandes spectrales élargir et décale vers le haut fréquence pour l'azote dopé nanotubes de carbone multi parois. Le décalage vers le haut fréquence pour l'acide sulfurique dopé double parois nanotubes de carbone est attribuée à transfert de charge et la déformation dans le réseau. Nous avons combiné le dopage de l'acide sulfurique et haute pression spectroscopie Raman pour étudier les propriétés de DWCNT. Le DWCNT dopé avec différentes concentrations d'acide sulfurique sous haute pression, suggère un effet de l'ordre des molécules autour de nanotubes à concentrations d'acide supérieur. Spectres Raman de double parois nanotube de carbone individual sur la silice en évidence un éclatement de la bande G grâce aux contributions du tube interne et externe lorsque utilisez une énergie d'excitation en résonance avec le tube métallique interne et tube semionducteurs externe. Les largeurs des bandes sont comparables à ce qui a été observé pour le nanotube de carbone monoparoi individul ou le graphène. Augmentation de la puissance du laser décale la bande G du tube extérieur vers les énergies plus élevées et modifie sa forme en ligneRaman spectroscopy is a non-invasive characterization technique suitable for the study of carbon nanotubes. Differences in the spectral shift of the Raman D and G bands are observed when heating carbon nanotubes through intense photon irradiation and by varying the temperature in a thermostat. These spectral changes in D mode are attributed to the variation of the electronic band structure by excitons creation. The investigation of the influence of doping and photoexcitation on the Raman G and D band of carbon nanotubes show that Raman spectroscopy can be used as a diagnostic tool. The spectral bands broaden and up shifts for nitrogen doped multi walled carbon nanotubes (MWCNT). The up shift for sulphuric acid doped double wall carbon nanotubes (DWCNT) synthesized from catalytic chemical vapor deposition method (CCVD) is attributed to charge transfer and strain in the lattice. We have combined sulphuric acid doping and high pressure Raman spectroscopy to investigate the properties of DWCNT. The DWCNT doped with different concentrations of sulphuric acid are explored under high pressure suggesting an effect of the molecular ordering around carbon nanotubes at higher acid concentrations. Raman spectra of individual double wall carbon nanotubes on silica show a splitting of the G band due to contributions of the inner and outer tube when using a excitation energy in resonance with the inner metallic tube and outer semiconducting tube. The spectral line widths are comparable to what has been observed for individual single wall carbon nanotubes (SWCNT) or graphene. Increased laser power shifts the G band of the outer tube to higher energies and modifies its line shape
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Sojoudi, Hossein. "The synthesis, doping, and characterization of graphene films." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50125.
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Graphene, a two-dimensional counterpart of three-dimensional graphite, has attracted significant interest, due to its distinctive electrical and mechanical properties, for developing electronic, optoelectronic, and sensor technologies. In general, doping of graphene is important, as it gives rise to p-type and n-type materials, and it adjusts the work function of the graphene. This adjustment is necessary in order to control charge injection and collection in devices such as solar cells and light emitting devices. Current methods for graphene doping involve high temperature process or interactions with chemicals that are not stable. Moreover, the process of transferring graphene from its growth substrate and its exposure to the environment results in a host of chemical groups that can become attached to the film and alter its electronic properties by accepting or donating electrons/holes. Intentional and controllable doping of the graphene, however, requires a deeper understanding of the impact of these groups. The proposed research will attempt to clarify the unintentional doping mechanism in graphene through adsorption or desorption of gas/vapor molecules found in standard environments. A low temperature, controllable and defect-free method for doping graphene layers will also be studied through modifying the interface of graphene and its support substrate with self-assembled monolayers (SAMs) which changes the work function and charge carriers in the graphene layer. Furthermore, current methods of chemical vapor deposition synthesis of graphene requires the film to be transferred onto a second substrate when the metal layer used for growth is not compatible with device fabrication or operation. To address this issue, the proposed work will investigate a new method for wafer scale, transfer-free synthesis of graphene on dielectric substrates using new carbon sources. This technique allows patterned synthesis on the target substrate and is compatible with standard device fabrication technologies; hence, it opens a new pathway for low cost, large area synthesis of graphene films.
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Pinto, Hugo Manuel. "Defects and dopants in carbon related materials." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3601.
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This thesis presents theoretical studies of the optical and electronic properties of defects in diamond and of the mechanisms of doping graphene. The birefringence of the four petalled defect commonly observed in CVD diamond is explained by four linear arrays of dislocations along ⟨110⟩ directions with ⟨110⟩ Burgers vectors. Such an arrangement of dislocations reproduces the extension and the features of the birefringence patterns observed experimentally. Density functional theory via the AIMPRO code was used to study the electronic and optical properties of different nitrogen-related point defects in diamond. It was found that the zero-phonon luminescence line of the NV− defects can split in the presence of a surface or other NV− defects. Since VNH and VN2 are expected to have similar optical properties, the optical transi- tions for VN2 were used to correct the transitions for VNH calculated by local density approximation. The absorption band at 2.38 eV (520 nm) observed in CVD diamond is then attributed to an internal transition of VNH. The weak zero-phonon line and broad vibronic sidebands for VN− and VN−2 and its absence for VNH− is explained by the large structural change when the defect is excited. Finally, different mechanisms for doping graphene were considered. The calculations predict the electropositive metals, such as Ti and Cr, act as donors, while molecules with strong electron affinity, such as F4-TCNQ, act as acceptors in graphene. An unexpected mechanism of doping graphene was shown by Au which dopes bilayer graphene but not single layer. In the presence of water, electrochemical reactions on the graphene can also lead to p or n-type doping.
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Villalpando, Paéz Federico. "Effects of doping single and double walled carbon nanotubes with nitrogen and boron." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36215.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 135-143).
Controlling the diameter and chirality of carbon nanotubes to fine tune their electronic band gap will no longer be enough to satisfy the growing list of characteristics that future carbon nanotube applications are starting to require. Controlling their band gap, wall reactivity and mechanical properties is imperative to make them functional. The solution to these challenges is likely to lie in smart defect engineering. Defects of every kind can induce significant changes on the intrinsic properties of carbon nanotubes. In this context, this thesis analyzes the effects of doping single and double walled carbon nanotubes with nitrogen and boron. We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (<10cm), via the thermal decomposition of ferrocene/ethanol/benzylamine (FEB) solutions in an Ar atmosphere at 950°C. Using Raman spectroscopy, we noted that as the N content is increased in the starting FEB solution, the growth of large diameter tubes is inhibited. We observed that the relative electrical conductivity of the strands increases with increasing nitrogen concentration. Thermogravimetric analysis (TGA) showed novel features for highly doped tubes, that are related to chemical reactions on N sites.
(cont.) We also carried out resonance Raman studies of the coalescence process of double walled carbon nanotubes in conjunction with high resolution transmission electron microscope (HRTEM) experiments on the same samples, heat treated to a variety of temperatures and either undoped or Boron doped. As the heat treatment temperatures are increased (to 1300°C) a Raman mode related to carbon-carbon chains (w = 1855cm-1) is observed before DWNT coalescence occurs. These chains are expected to be 3-5 atoms long and they are established covalently between adjacent DWNTs. The sp carbon chains trigger nanotube coalescence via a zipper mechanism and the chains disappear once the tubes merge. Other features of the Raman spectra were analyzed as a function of heat treatment with special emphasis on the metallic or semiconducting nature of the layers constituting the DWNTs. DWNTs whose outer wall is metallic tend to interact more with the dopant and their outer tubes are the predominant contributors to the line shape of the G and G' bands.
(cont.) The metallic or semiconducting nature of the layers of the DWNTs does not affect their coalescence temperature. All the experiments and analysis presented in this thesis are the result of a collaborative effort between Professor Dresselhaus' group at MIT and its international collaborators, including Professor Endo's group at Shinshu University, Nagano, Japan, Professors Pimenta's and Jorio's group at the Federal University of Minas Gerais, Belo Horizonte, Brazil, and Professors M. and H. Terrones' group at IPICYT, San Luis Potosi, Mexico.
by Federico Villalpando Paéz.
S.M.
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Chindanon, Kritsa. "Nitrogen doping in low temperature halo-carbon homoepitaxial growth of 4H-silicon carbide." Master's thesis, Mississippi State : Mississippi State University, 2008. http://library.msstate.edu/etd/show.asp?etd=etd-07102008-045510.
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Hopkin, Amy L. "Methane conversion over supported nickel catalysts : influence of gold doping, support material and preparation method." Thesis, Keele University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288499.
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Esmaeili, Mostafa. "The Effects of Nitrogen doping on Chemical, Optical and Electronic properties of Carbon Dots." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/414280.
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Photoluminescent carbon dots have received significant research interest in recent years owing to their extraordinary optical properties, biocompatibility, and versatile functionalities. Nitrogen-doping is a widely used strategy for enhancing the photoelectronic functionalities of carbon dots. However, there is a lack of systematic study on the composition and concentration-dependency emission behaviour of N-doped carbon dots in the literature. In this study, multicolour carbon dots (CDs) having different degree of nitrogen doping were synthesized by varying the molar ratio of citric acid to urea in the precursor via hydrothermal treatment. The effects of nitrogen doping on chemical, optical, and electronic properties of CDs were characterized using various techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR); fluorescence and absorption spectroscopy; fluorescence lifetime and Hall effect measurements. Three main emissive centres were recognized in concentration-dependent fluorescence study of N-CDs which can be ascribed to molecular type of fluorescence, core emission, and mid-gap nitrogen states on the edge/surface of CDs. A plausible mechanism in relation to the obtained results is proposed. This work provides insights on the opto-electro-tunability of CDs via N-doping.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Mawudoku, Daniel, George Affadu_Danful, Caitlin Millsaps, and Gregory Bishop. "Immobilization of Electrocatalytically Active Gold Nanoparticles on Nitrogen-Doped Carbon Fiber Electrodes." Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/asrf/2019/schedule/106.
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Immobilization of Electrocatalytically Active Gold Nanoparticles on Nitrogen-Doped Carbon Fiber Electrodes
ABSTRACT
Recently, immobilization of single metal nanoparticles on nanometer-sized electrodes has been demonstrated as a means to electrochemically probe the relationship between nanoparticle structure and function. Such studies of individual, isolated nanoparticles enable investigation of electrochemical behavior and electrocatalytic properties in the absence of complicating factors like interparticle distance and nanoparticle loading that are typically associated with collections of particles distributed on electrode supports. However, interpretation of electrochemical data obtained from single nanoparticle immobilization experiments can also be difficult since the underlying nanoelectrode platform can sometimes contribute to the measured current or the immobilization strategy may have adverse effects on electron transfer. Here we report immobilization of gold nanoparticles on relatively catalytically inert carbon fiber ultramicro- and nanoelectrodes through a modification method based on recently reported soft nitriding process found to be effective in attaching ligand-free ultrasmall noble metal catalysts to activated carbons. X-ray photoelectron spectroscopy results reveal that the nitriding of carbon fibers provides 3.5 times increase in surface nitrogen content, introducing mostly pyridinic and amine nitrogen groups. The nitrogen-containing surface sites proved to be beneficial to the deposition of gold nanoparticles (AuNPs), as sodium borohydride reduction of tetrachloroaurate resulted in attachment of AuNPs on nitrided carbon fiber ultramicroelectrodes (N-CF-UMEs) in as little as 10 seconds while immobilization of AuNPs on unmodified CF-UMEs required at least 12 hours. A recently reported electrochemical method was employed to characterize immobilized AuNPs, and AuNP size was found to be directly related to deposition time. AuNPs immobilized on N-CF-UMEs also exhibited electrocatalytic activity towards methanol oxidation. Reduction of electrode size will enable this strategy to be employed to investigate electrochemical behavior of individual gold nanoparticles, while the ligand-free nature of the immobilized particles also provides the opportunity to investigate effects of surface capping agents on electrocatalytic properties.
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Ye, Jianting. "Fabrication analysis and lithium doping in 4 Å carbon nanotubes in the channels of AlPO4̳-5 crystal /." View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202002%20YE.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002.On t.p. "4̳" is subscript. Includes bibliographical references (leaves 84-86). Also available in electronic version. Access restricted to campus users.
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Kuo, Ming-Tsun. "Field emission and annealing studies of n-type doped hydrogenated amorphous carbon films." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340300.
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Webb, Kimberly Faye. "Synthesis, blending, and doping of electrically conducting poly(3-undecylbithiophene) in supercritical carbon dioxide." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/10129.
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Lardeau-Falcy, Aurélien. "Dopage de couches de GaN sur substrat silicium par implantation ionique." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY024/document.
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Les dispositifs à base de GaN et ses alliages sont de plus en plus présents dans notre quotidien avec le développement exponentiel des diodes électroluminescentes (LED). Bien que la majorité des productions commerciales soient pour le moment effectuées sur substrat saphir, le silicium, disponible en de plus grands diamètres et pour un coût moindre, est de plus en plus pressenti comme le substrat d’avenir pour le développement des technologies GaN. L’utilisation de ce substrat devrait aussi permettre le développement du marché de l’électronique de puissance du GaN basée sur les transistors à haute mobilité électronique (HEMT) dont les performances dépassent les limites des technologies silicium. Néanmoins, afin de permettre ou faciliter le développement de dispositifs avancés, certaines briques technologiques sont nécessaires comme le dopage par implantation ionique. L’utilisation du GaN soulève des problématiques nouvelles pour ces briques technologiques.Au cours de cette thèse nous avons donc cherché à implémenter le procédé de dopage par implantation ionique du GaN et son étude au sein du CEA-LETI en nous focalisant principalement sur le dopage p par implantation de Mg. Nous avons identifié les principales problématiques liées aux propriétés intrinsèques du matériau (difficulté du dopage p, instabilité à haute température…) et les solutions les plus prometteuses de la littérature. Nous avons ensuite cherché à mettre en place notre propre procédé en développant des couches de protection déposées in-situ pour permettre les traitements thermiques à haute température des couches implantées. Cela a rendu possible l’étude des cinétiques d’évolution des couches implantées pendant des recuits « conventionnels » (rampes < 10 °C/min, durée de plusieurs dizaines de minutes, T < 1100 °C) en utilisant notamment des caractérisations de photoluminescence (µ-PL) et de diffraction des rayons X (XRD). Nous avons aussi mis en évidence un effet de diffusion et d’agrégation à haute température du Mg implanté. Nous avons ensuite cherché à modifier le procédé d’implantation (implantation canalisée, co-implantation) pour favoriser l’intégration du dopant et limiter la formation de défauts. En parallèle nous avons évalué l’intérêt de recuits secondaires (recuits rapides (RTA), recuit laser, micro-ondes) afin de finaliser l’activation du dopant. Finalement nous avons aussi mis en place un procédé de caractérisation électrique de couche de GaN dopées au sein du laboratoireGaN-based devices and their alloys are increasingly present in our daily lives with the exponential development of light-emitting diodes (LEDs). Although the majority of commercial production is currently carried out on sapphire substrates, silicon, available in larger diameters and at a lower cost, is increasingly seen as the substrate of the future for the development of GaN technologies. The use of this substrate should also allow the development of the GaN power electronics market based on high electron mobility transistors (HEMTs) whose performances exceed the limits of silicon technologies. Nevertheless, in order to allow or facilitate the development of advanced devices, specific processes are necessary such as doping by ion implantation. The use of GaN raises new problems for these technological bricks.During this thesis we therefore sought to implement the ion implantation doping process of GaN and its study within the CEA-LETI while focusing mainly on p doping by Mg implantation. We have identified the main issues related to the intrinsic properties of the material (difficulty of p-doping, instability at high temperatures...) and the most promising solutions in the literature. We then sought to implement our own process by developing in-situ protective layers to allow high temperature annealing of the implanted layers. This enabled the study of the evolution kinetics of the implanted layers during "conventional" annealing (ramps < 10 °C/min, duration of several tens of minutes, T < 1100 °C) using photoluminescence (µ-PL) and X-ray diffraction (XRD) characterizations. We also evidenced a diffusion and aggregation effect at high temperature of the implanted Mg. We then sought to modify the implantation process (channeled implantation, co-implantation) to promote the integration of the dopant and limit the formation of defects. In parallel we evaluated the interest of secondary annealing (Rapid thermal annealing (RTA), laser annealing, microwave) in order to finalize the activation of the dopant. Finally we also set up an electrical characterization process for doped GaN layers in the laboratory
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Zhong, Mingyu. "Doped GaN grown by Phase Shift Epitaxy, fabrication and characterization of GaN:Eu LED." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384427470.
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Ive, Tommy. "Growth and investigation of AlN/GaN and (Al,In)N/GaN based Bragg reflectors." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2006. http://dx.doi.org/10.18452/15395.
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Die Synthese von AlN/GaN- und (Al,In)N/GaN-Braggreflektoren wird untersucht. Die Strukturen wurden mittels plasmaunterstützter Molekularstrahlepitaxie auf 6H-SiC(0001)-Substraten abgeschieden. Ferner wurde der Einfluß der Si-Dotierung auf die Oberflächenmorphologie sowie die strukturellen und elektrischen Eigenschaften der AlN/GaN-Braggreflektoren untersucht. Es wurden rißfreie Braggreflektoren mit einer hohen Reflektivität (R>99%) und einem bei 450 nm zentrierten Stopband erhalten. Die Si-dotierten Strukturen weisen eine ohmsche I-V-Charakteristik im gesamten Meßbereich sowie einen spezifischen Widerstand von 2-4 mOhmcm2 auf. Die Ergebnisse der (Al,In)N-Wachstumsversuche wurden in einem Phasendiagramm zusammengefaßt, welches den optimalen Parameterraum für (Al,In)N klar aufzeigt.We study the synthesis of AlN/GaN and (Al,In)N/GaN Bragg reflectors. The structures were grown by plasma-assisted molecular beam epitaxy (MBE) on 6H-SiC(0001) substrates. In addition, we study the impact of Si-doping on the surface morphology and the structural and electrical properties of the AlN/GaN Bragg reflectors. Crack-free and high-reflectance (R>99%) Bragg reflectors were achieved with a stopband centered at 450 nm. The Si-doped structures exhibit ohmic I-V behavior in the entire measurement range. The specific series resistance is 2-4 mOhmcm2. The results of the (Al,In)N growth experiments are summarized in a phase diagram which clearly shows the optimum growth window for (Al,In)N.
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Ajay, Akhil. "Nanofils de GaN/AlGaN pour les composants quantiques." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY030/document.
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Ce travail se concentre sur l'ingénierie Intersubband (ISB) des nanofils où nous avons conçu des hétérostructures de GaN / (Al, Ga) N intégrées dans un nanofil GaN pour le rendre optiquement actif dans la région spectrale infrarouge (IR), en utilisant un faisceau moléculaire assisté par plasma épitaxie comme méthode de synthèse. Les transitions ISB se réfèrent aux transitions d'énergie entre les niveaux confinés quantiques dans la bande de conduction de la nanostructure.Un contrôle précis des niveaux élevés de dopage est crucial pour les dispositifs ISB. Par conséquent, nous explorons Ge comme un dopant alternatif pour GaN et AlGaN, pour remplacer le Si couramment utilisé. Nous avons cultivé des couches minces de GaN dopé Ge avec des concentrations de porteurs atteignant 6,7 × 1020 cm-3 à 300 K, bien au-delà de la densité de Mott, et nous avons obtenu des couches minces conductrices AlxGa1-xN dopées Ge avec une fraction molaire Al jusqu'à x = 0,64. Dans le cas de GaN, la présence de Ge n'affecte pas la cinétique de croissance ou les propriétés structurales des échantillons. Cependant, dans des échantillons AlxGa1-xN dopés par Ge avec x> 0,4, la formation de grappes riches en Ge a été observée, avec une baisse de la concentration du porteur.Ensuite, nous avons réalisé une étude comparative du dopage Si vs Ge dans des hétérostructures GaN / AlN pour des dispositifs ISB dans la gamme IR à courte longueur d'onde. Nous considérons les architectures planaire et nanofils avec des niveaux de dopage et des dimensions de puits identiques. Sur la base de cette étude, nous pouvons conclure que les deux Si et Ge sont des dopants appropriés pour la fabrication d'hétérostructures GaN / AlN pour l'étude des phénomènes optoélectroniques ISB, à la fois dans les hétérostructures planaires et nanofils. Dans cette étude, nous rapportons la première observation de l'absorption d'ISB dans des puits quantiques GaN / AlN dopés au Ge et dans des hétérostructures de nanofils GaN / AlN dopés au Si. Dans le cas des nanofils, nous avons obtenu une largeur de ligne d'absorption ISB record de l'ordre de 200 meV. Cependant, cette valeur est encore plus grande que celle observée dans les structures planaires, en raison des inhomogénéités associées au processus de croissance auto-assemblé.En essayant de réduire les inhomogénéités tout en gardant les avantages de la géométrie des nanofils, nous présentons également une analyse systématique de l'absorption de l'ISB dans les micro et nanopillars résultant d'un traitement top-down des hétérostructures planaires GaN / AlN. Nous montrons que lorsque l'espacement du réseau de piliers est comparable aux longueurs d'onde sondées, les résonances des cristaux photoniques dominent les spectres d'absorption. Cependant, lorsque ces résonances sont à des longueurs d'onde beaucoup plus courtes que l'absorption ISB, l'absorption est clairement observée, sans aucune dégradation de son amplitude ou de sa largeur de raie.Nous explorons également la possibilité d'étendre cette technologie de nanofils à des longueurs d'onde plus longues, pour les absorber dans la région IR à mi-longueur d'onde. En utilisant des hétérostructures de nanofils GaN / AlN, nous avons fait varier la largeur du puits GaN de 1,5 à 5,7 nm, ce qui a conduit à un décalage rouge de l'absorption ISB de 1,4 à 3,4 μm. Remplaçant les barrières AlN par Al0.4Ga0.6N, le composé ternaire représente une réduction de la polarisation, ce qui conduit à un nouveau décalage rouge des transitions ISB à 4,5-6,4 um.L'observation de l'absorption de l'ISB dans des ensembles de nanofils nous a motivés pour le développement d'un photodétecteur infrarouge à puits quantiques à base de nanofils. La première démonstration d'un tel dispositif, incorporant une hétérostructure de nanofils GaN / AlN qui absorbe à 1,55 μm, est présentée dans ce manuscritDue to its novel properties nanowires have emerged as promising building blocks for various advanced device applications. This work focuses on Intersubband (ISB) engineering of nanowires where we custom design GaN/(Al,Ga)N heterostructures to be inserted in a GaN nanowire to render it optically active in the infrared (IR) spectral region. ISB transitions refer to energy transitions between quantum confined levels in the conduction band of the nanostructure. All the structures analised in this thesis were synthesized by plasma-assisted molecular beam epitaxy.Precise control of high doping levels is crucial for ISB devices. Therefore, we explored Ge as an alternative dopant for GaN and AlGaN, to replace commonly-used Si. We grew Ge-doped GaN thin films with carrier concentrations of up to 6.7 × 1020 cm−3 at 300 K, well beyond the Mott density, and we obtained conductive Ge-doped AlxGa1-xN thin films with an Al mole fraction up to x = 0.66. In the case of GaN, the presence of Ge does not affect the growth kinetics or structural properties of the samples. However, in Ge doped AlxGa1-xN samples with x > 0.4 the formation of Ge rich clusters was observed, together with a drop in the carrier concentration.Then, we performed a comparative study of Si vs. Ge doping in GaN/AlN heterostructures for ISB devices in the short-wavelength IR range. We considered both planar and nanowire architectures with identical doping levels and well dimensions. Based on this study, we concluded that both Si and Ge are suitable dopants for the fabrication of GaN/AlN heterostructures for the study of ISB optoelectronic phenomena, both in planar and nanowire heterostructures. Within this study, we reported the first observation of ISB absorption in Ge-doped GaN/AlN quantum wells and in Si-doped GaN/AlN nanowire heterostructures. In the case of nanowires, we obtained a record ISB absorption linewidth in the order of 200 meV. However, this value is still larger than that observed in planar structures, due to the inhomogeneities associated to the self-assembled growth process.Trying to reduce the inhomogeneities while keeping the advantages of the nanowire geometry, we also presented a systematic analysis of ISB absorption in micro- and nanopillars resulting from top-down processing GaN/AlN planar heterostructures. We showed that, when the spacing of the pillar array is comparable to the probed wavelengths, photonic crystal resonances dominate the absorption spectra. However, when these resonances are at much shorter wavelengths than the ISB absorption, the absorption is clearly observed, without any degradation of its magnitude or linewidth.We also explore the possibility to extend this nanowire technology towards longer wavelengths, to absorb in the mid-wavelength IR region. Using GaN/AlN nanowire heterostructures, we varied the GaN well width from 1.5 to 5.7 nm, which led to a red shift of the ISB absorption from 1.4 to 3.4 µm. Replacing the AlN barriers by Al0.4Ga0.6N, the reduction of polarization led to a further red shift of the ISB transitions to 4.5-6.4 µm.The observation of ISB absorption in nanowire ensembles motivated us for the development of a nanowire-based quantum well infrared photodetector (NW-QWIP). The first demonstration of such a device, incorporating a GaN/AlN nanowire heterostructure that absorbs at 1.55 µm, is presented in this manuscript
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Wornyo, Eric. "Nitrogen-Doped Carbon Fiber Ultramicroelectrodes as Electrochemical Sensors for Detection of Hydrogen Peroxide." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3960.
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Carbon fiber ultramicroelectrodes (CF-UMEs) are commonly used as electrochemical probes and sensors due to their small size, fast response, and high signal-to-noise ratio. Surface modification strategies are often employed on CF-UMEs to improve their selectivity and sensitivity for desired applications. However, many modification methods are cumbersome and require expensive equipment. In this study, a simple approach known as soft nitriding is used to prepare nitrogen-doped CF-UMEs (N-CF-UMEs). Nitrogen groups introduced via soft nitriding act as electrocatalytic sites for the breakage of O-O bonds during the reduction of peroxides like H2O2, a common target of biosensing strategies. Voltammetric studies confirm that, compared to CF-UMEs, N-CF-UMEs possess enhanced electrocatalytic activity towards H2O2 reduction as evidenced by an increase in current and positive shift in onset potential for the reaction. N-CF-UMEs also proved capable for amperometric detection of H2O2, exhibiting good linear response from 0.1 to 5.6 mM at -0.4 V vs. Ag/AgCl.
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Hoy, Daniel R. "Gallium Nitride and Aluminum Gallium Nitride Heterojunctions for Electronic Spin Injection and Magnetic Gadolinium Doping." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1331855661.
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Kanakaraj, Sathya Narayan. "Processing Carbon Nanotube Fibers for Wearable Electrochemical Devices." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1573224577754985.
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Macpherson, Ross Fraser. "Monte Carlo modelling of Gunn devices incorporating thermal heating effects : investigations of broad frequency devices, heating effects in GaN devices and doping nucleation." Thesis, University of Aberdeen, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=203872.
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Monte Carlo modelling is a common technique in numerous fields, and is widely used in semiconductor device simulation. This thesis describes the application of Monte Carlo modelling to the simulation of Gunn diode devices, focusing on devices composed of Gallium Arsenide (GaAs) and Gallium Nitride (GaN). Gunn diodes are simple structures that take advantage of negative differential resistance to act as a source of high frequency radiation, from 10 GHz to over 100 GHz in GaAs devices. It has been theorised that GaN should exhibit negative differential resistance and a GaN Gunn diode could produce radiation of even higher frequency, within the terahertz band. Gunn diodes have the advantage of being cheap and portable, and so are worth exploring as such a source. Unfortunately, GaN devices have a high electron density and so they tend to generate heat quickly. It therefore becomes important to include modelling of heat generation and flow in simulations of these devices. This is uncommon in Monte Carlo models of Gunn diodes, as in less highly doped devices thermal effects can usually be assumed to result in the device reaching an equilibrium temperature of about 100 K above the ambient. This thesis describes the creation of a model to track the generation and distribution of heat during operation of a GaN device. Simulations found that thermal effects within the device were significant. Heat generation occurred to the extent that the device could only be operated in pulsed mode, with on pulses of 2 ns requiring 50 ns of cooling for sustainable operation. The increased temperature within the device also lead to deleterious changes in the Gunn diode's operating frequency. In the simulated device, a 150 K change in temperature lead to a decrease in operating frequency of 40 GHz, from an initial frequency of 280 GHz. At the end of 2 ns of operation, the mean temperature within the device had increased by 120 K. The high accidental doping level in GaN also means the use of a doping notch to act as a nucleation point for dipoles within a Gunn diode, a common technique in other materials, becomes less feasible. As an alternative to a notch, a device was simulated incorporating a doping spike to nucleate the dipole. The use of a doping spike is not novel, however its use in GaN has not been previously explored. Simulations found that a fully-depleted p-type doping notch of length 2.1 nm, doped at 1x1024 m-3 would act as a nucleation point for dipole operation. The device was compared to a simulated device incorporating a doping notch of width 0.25 µm doped at 0.5x1023 m-3 and found to operate at a similar frequency and RF efficiency, making it a viable substitute. One limitation of Gunn diodes is that when operated in transit-time mode, the operating frequency is determined by the length of the diode's transit region and so is well-defined and fixed. This means that traditional Gunn diodes are not as useful a source of radiation for spectroscopic applications as might be desirable. Recent experimental results for planar devices have shown a broadening in operation frequency and even multiple frequencies. This thesis explores the hypothesis that such a broadening might be achieved in a vertical structure via the incorporation of an additional notch into the Gunn diode's transit region, effectively incorporating two transit regions into the device. Results showed that this novel device structure did show multiple modes of operation. Under a DC applied voltage, the device showed spontaneous switching behaviour, oscillating between dipole and accumulation layer operation from the second notch. Changes in the frequency of an applied RF voltage would shift the device from operating from the first or second notch, in dipole and accumulation layer mode respectively.
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Sun, Yue-Jun. "Growth and characterization of M-plane GaN and (In, Ga)N/GaN multiple quantum wells." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97256375X.
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Mishra, Siddharth. "Plasma Enhanced Synthesis of Novel N Doped Vertically Aligned Carbon Nanofibers-3D Graphene hybrid structure." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1552380299631335.
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Xhyliu, Fjorela. "Surface Functionalization and Optical Spectroscopy of Single-wall Carbon Nanotubes." Cleveland State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=csu1599143727075125.
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Davies, Sean. "In-situ optical monitoring of growth processes during the carbon doping and nitridation of GaAs in CBE." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399266.
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HINOJOSA, PAOLA ALEXANDRA AYALA. "IMPLICATIONS OF THE C/N FEEDSTOCK ON CONTROLLING THE NITROGEN DOPING AND BONDING ENVIRONMENT IN CARBON NANOTUBES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=10399@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOOs tópicos mais importantes a ser tratados nesta tese de doutorado são os vários problemas envolvidos na síntese de nanotubos contendo nitrogênio. Isto é principalmente motivado pelas possíveis aplicações que podem ser dadas a este tipo de estruturas. A motivação central está relacionada ao fato da possibilidade de fazer dopagens tipo -p e -n em nanotubos de carbono, incorporando átomos como boro ou nitrogênio. Isto está muito longe de ser uma trivialidade devido a que devemos levar em conta que se os nanotubos de carbono forem pensados como bases estruturais para nanocompósitos e dispositivos nanoeletronicos, é necessário controlar cuidadosamente a reatividade das paredes, sua dureza mecânica e o gap eletrônico por meio de um controle da quantidade de átomos inseridos nas paredes ou entre elas. Portanto, do ponto de vista de diferentes aplicações, é importante ter a possibilidade de dopar controladamente os nanotubos. Neste trabalho apresentam-se o quadro descritivo da dependência dos parâmetros de síntese, assim como uma investigação detalhada da formação de outras estruturas co-produto do processo de formação de nanotubos. Como uma idéia pioneira proposta neste trabalho, é enfatizado o uso de fontes puras de C/N em processos de síntese baseados em deposição química na fase de vapor. Desta maneira foi possivel determinar os efeitos da atmosfera de reação e o pretratamento do catalizador como agentes favoráveis ou desfavoráveis para a síntese efetiva de nanotubos de carbono.
The main topic of this thesis is the study of various issues related to the synthesis of nitrogen containing nanotubes. This is mainly inspired in the possible applications such structures can have. The practical background lies in the fact that defined n- and p-doping of carbon nanotubes can be achieved by substituting carbon atoms from the tube walls by heteroatoms such as boron or nitrogen (N). This is far from been a triviality because we must keep in mind that if carbon nanotubes are to be used as future building blocks in nanocomposites and nanoelectronic devices, it is imperative to fine tune their wall reactivity, mechanical strength and electronic band gap by controlling the amount of foreign atoms inserted into the tube lattices. Therefore, from an applications standpoint, it is important to be able to carefully control the insertion of different dopants into nanotubes. In this work, a complete picture of the dependence on the combined synthesis parameters is established and a fundamental insight into the formation of N doped nanotubes and other structures (co- products) is provided. As a pioneering idea of this whole work, the use of pure C/N feedstocks in chemical vapor deposition methods is emphasized. With this, it was possible to determine the effects of the reaction atmosphere and the catalyst pretreatment as either favoring or disfavoring agents towards the synthesis of N-doped nanotubes.
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Haugen, Neale O. "Spectroscopic Studies of Doping and Charge Transfer in Single Walled Carbon Nanotubes and Lead Sulfide Quantum Dots." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438768843.
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Ogbu, Chidiebere. "Peroxide Sensing Using Nitrogen-Doped and Platinum Nanoparticle-modified Screen-Printed Carbon Electrodes." Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/etd/3622.
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Nitrogen-doped carbon materials have garnered much interest due to their abilities to behave as electrocatalysts for reactions important in energy production (oxygen reduction) and biosensing (hydrogen peroxide reduction). Here, we demonstrate fabrication methods and determine electrocatalytic properties of nitrogen-doped screen-printed carbon (N-SPCE) electrodes. Nitrogen doping of graphite was achieved through a simple soft-nitriding technique which was then used in lab-formulated screen-printing inks to prepare N-SPCEs. N-SPCEs displayed good electrocatalytic activity, reproducibility and long term stability towards the electrochemical reduction of hydrogen peroxide. N-SPCEs exhibited a wide linear range (20 µM to 5.3 mM), reasonable limit of detection of 2.5 µM, with an applied potential of -0.4 V (vs. Ag/AgCl). We also demonstrate that nitrided-graphite can similarly be used as a platform for the deposition of electrocatalytic platinum nanoparticles, resulting in Pt-N-SPCEs with a lower limit of detection (0.4 µM) and better sensitivity (0.52 µA cm-2 µM-1) towards H2O2 reduction.
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Vorobiov, Mykhailo. "PHOTOLUMINESCENCE FROM GAN CO-DOPED WITH C AND SI." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5496.
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This thesis devoted to the experimental studies of yellow and blue luminescence (YL and BL relatively) bands in Gallium Nitride samples doped with C and Si. The band BLC was at first observed in the steady-state photoluminescence spectrum under high excitation intensities and discerned from BL1 and BL2 bands appearing in the same region of the spectrum. Using the time-resolved photoluminescence spectrum, we were able to determine the shape of the BLC and its position at 2.87 eV. Internal quantum efficiency of the YL band was estimated to be 90\%. The hole capture coefficient of the BLC related state was determined as 7 10-10 cm3/s. Properties of BLC were investigated. The YL and BLC bands are attributed to electron transitions via the (0/-) and (+/0) transition levels of the CN defect.
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Mokhtari, Hossein. "Transmission electron microscopy of defects and internal fields in GaN structures." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368206.
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Remesh, Nayana. "Investigation of Buffer Design and Carbon doping in AlGaN/GaN HEMTs for High Breakdown Voltages." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5463.
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III-nitride HEMTs are strong contenders for next-generation power electronic applications. The superior material and electrical properties render GaN-based transistors suitable for high-power switching. The material characteristics such as high breakdown voltage, high electron mobility, and high operating temperature make GaN score over Si. Further, low ON resistance and high switching speed responsible for the subsequent reduction in both switching and ON/OFF state losses render GaN-based HEMT a foreboding device for power electronic applications.
In this Doctoral Dissertation, we investigate the impact of epitaxial stack design and transistor architecture on the breakdown voltage characteristics and dynamic performances of AlGaN/GaN HEMT for power switching applications. The focus of the thesis starts with understanding the effect of threading dislocations in vertical leakage. This study discusses the mechanism of dislocation-mediated vertical leakage in MOCVD-grown Carbon (C)-doped AlGaN/GaN HEMTs on a 6-inch silicon wafer. Substrate bias polarity-dependent I-Vs, temperature-dependent fitting, and band diagram analysis pointed to the Poole-Frenkel type of conduction mechanism for vertical transport in the devices. We propose that higher dislocation density leads to shallower traps in the buffer and build an analytical model of dislocation-mediated vertical leakage around this.
Based on the above evidence, vertical leakage can be reduced in an epitaxial HEMT stack with a higher dislocation density by introducing carbon. It reduces the unintentional doping in GaN, which acts as a carrier, conducted through the dislocation mediated leakage paths. Initially, we tried to incorporate carbon in GaN buffer by reducing the growth temperature, i.e., by auto doping and using CBr4 as an external source. The later part of the chapter reports on the experimental and analytical determination of the optimum carbon concentration in GaN to achieve enhanced breakdown voltage (voltage @ 1 A/cm2) in AlGaN/GaN HEMTs.
Later, in the work, we tried to study the step-graded AlGaN transition layers (TL) in the HEMT stack to improve the breakdown voltage. The transition layers include three AlGaN epi-layers of 75%, 50%, and 25% Al-content, down-graded from bottom to top. The growth temperature and carbon doping are varied independently to assess the transition layer's role in leakage current. The introduction of C-doping in the top AlGaN transition layer with 25% Al-content improves lateral breakdown voltage in both mesa and 3-terminal configurations. The combination of HT AlGaN (75% Al-content) with C-doped AlGaN (25% Al-content) is found to be the optimal TL design.
After optimizing the stack for low off-state leakage current, we focused on evaluating the on-state performance of the AlGaN/GaN HEMT. In GaN HEMT devices, dynamic RON is considered the most crucial issue in high voltage switching applications. Dynamic RON is a phenomenon in which the on-resistance (RON) of the device increases under high voltage switching conditions. This chapter tried to analyze the effect of growth variations like carbon doping and high growth temperatures on dynamic RON.
A subtle balance between HEMT epitaxial stack and device design is crucial to achieving a high breakdown voltage in AlGaN/GaN HEMT. One of the main hurdles in the device design is surface passivation. In this work, we have investigated the material properties of PECVD (Plasma Enhanced Chemical Vapor Deposition) deposited amorphous SiN films and their influence on leakage current of AlGaN/GaN HEMT grown on Si. The device architecture is further improved by incorporating gate field plate design using the optimized SiN to enhance the breakdown voltage by distributing an electric field in the gate to the drain access region.
In conclusion, we propose epitaxial stack design guidelines to achieve high breakdown voltage with low dynamic RON. The optimized epitaxial stack of 1.65 µm has the potential to be converted as a cost-effective technology for high voltage applications (400 V), which is in demand in the EV industry.
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Chou, Chia Yi, and 周佳逸. "Influence of Buffer Carbon Doping and Buffer Thickness on Low Frequency Noise Behavior of AlGaN/GaN HEMTs." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/96035991629482509484.
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Hsu, Miao-Chih, and 徐妙枝. "Isoelectronic Indium Doping Effects On P-type GaN Films." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/22909728328174972455.
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碩士國立交通大學
電子物理系
90
We have investigated the isoelecetronic indium doping effects of Indium on p-type GaN films. Two sets of samples were prepared：one is pure Mg-doped GaN film, the other is Mg-In codoped GaN film. Whether Indium is doped or not, the photoluminescence spectra of as-grown p-type GaN films all show one broad emission peak around 2.78eV, which indicating Mg-rich in all of our p-type GaN samples. Besides, it is interesting to note that the hole concentration of Mg-In codoped GaN is higher than that of Mg-doped one based on room-temperature Hall measurement data. The optimum hole concentration is 7.32´1017cm-3. We believe the increase of the hole concentration in these indium doped p-GaN films can be attributed primarily to the reduction of the acceptor activation energy, the decrease of compensation effects as well as effective incorporation of Mg atom as shallow acceptor, rather than deep impurity, not directly related to the Mg solid concentration in the film.
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Fu-Min, Wang, and 王富民. "Investigation of AlGaN/GaN Doping-Channel High Electron Mobility Transistors." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/75941597127919252758.
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碩士國立高雄師範大學
電子工程學系
103
Investigation of AlGaN/GaN Doping-Channel High Electron Mobility Transistors Fu-Min Wang* Jung-Hui Tsai** Department of Electronics, National Kaohsiung Normal University, Kaohsiung, Taiwan, R.O.C Abstract In this dissertation, we will fabricate and investigate the impact of doping channel on the AlGaN/GaN doping-channel high electron mobility transistors, and the influence of doped thickness on AlGaN/GaN doping-channel high electron mobility transistors will be included. The structures were designed as follows: (1) AlGaN/GaN doping-channel high electron mobility transistor with channel doping region thickness of 20 nm (called Device A). (2) AlGaN/GaN high electron mobility transistor without GaN doping-channel layer (called Device B). (3) AlGaN/GaN doping-channel high electron mobility transistor with a channel doping region thickness of 19.5, 19, 17.5, 15, 10, and 5 nm, respectively, and with a spacer close to the AlGaN/GaN heterojunction of 0.5, 1, 2.5, 5, 10, and 15 nm, respectively (called Devices C, D, E, F, G, and H). The device (Device A) was fabricated by metal-organic chemical vapor deposition system on a sapphire substrate. The experimental results exhibit a maximum drain saturation current of 506.9 mA/mm and a maximum transconductance of 52.475 mS/mm. Also, we will simulate the DC performance of device A with doping channel according to the experimental data. The simulated characteristics are close to the experimental results by choosing the proper parameters. Simulation results show that the 2DEG concentration of the device A is higher than the device B without the doping-channel layer. The doping channel will enable the 2DEG concentration to increase. However, the impurity scattering of carriers in the doping channel will lead to the electron mobility to decrease. The results show that the device A with a doping channel has poor output saturation current, transconductance, gate leakage current, breakdown voltage, and high-frequency characteristics. In addition, the doping layer of devices C, D, E, F, G, and H are away from the 2DEG. It can decrease the effect of impurity scattering. The result exhibits that the DC and high-frequency characteristics of the devices F, G, and H are better than the device B. In the devices F, G, and H, the 2DEG carrier concentrations are 1.158 × 1020, 1.155 × 1020, and 1.154 × 1020 cm-3, the maximum output currents are of 672, 682, and 689.7 mA/mm, and transconductance are 84.4, 87, and 89.4 mS/mm, respectively. Furthermore, the unity gain cut-off frequencies are 17.8, 18.1, and 18.3 GHz, and maximum oscillation frequencies are 28.3, 29.1, and 29.2 GHz respectively. * Author ** Advisor KEYWORDS : AlGaN/GaN, high electron mobility transistor, doping channel, impurity scattering
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Maubane, Manoko Stephina. "Synthesis, doping and functionalization of carbon nanotubes." Thesis, 2011. http://hdl.handle.net/10539/9148.
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This study reports the synthesis of carbon nanotubes (CNTs) incorporated into polymeric
materials for potential use in photovoltaic solar cells. Both undoped (CNTs) and nitrogendoped
(N-CNTs) materials were made using the chemical vapor deposition (CVD), catalytic
CVD and floating catalyst CVD methods. The procedures produced CNTs with an average
yield of 1151 % using a 10 % Fe/Co catalyst supported on CaCO3. This is about three times
that produced using 5 % Fe/Co catalyst (average 409 %). Morphology studies showed that the
synthesized materials had an average diameter of 30 nm. CNTs were successfully incorporated
into polythiophenes (PTh) using an in situ chemical oxidative polymerization method. TEM
images showed that the functionalized CNTs in polythiophene, f-CNT/PTh, were thicker
(average 192 nm) as compared to pristine CNTs (30 nm). TGA analysis then revealed that the
new materials (f-CNT/PTh) were more thermally stable as compared to the pure polymer.
N-CNTs were synthesized by the floating catalyst CVD method using toluene, ferrocene and
tetramethylethylenediamine. Functionalization of the N-CNTs was then achieved using 3-
thiophenecarboxaldehyde and sarcosine in 1,2-dichlorobenzene (Prato reaction). Elemental
analysis showed nitrogen incorporation (1.8%) into the N-CNTs and this value tripled after
functionalization with the nitrogen donor reagents. Morphology studies showed that the amount
of monomer used in forming the N-CNT/PTh nanostructures had an influence on the average
diameters of the materials. Different ratios of nanotubes to thiophene monomer by weight were
used (1:3, 1:10 and 1:20). It was found that when the amount of thiophene monomer was
increased, the overall diameter of the materials increased as did the thickness of the polymer
attached onto the N-CNTs. Similar studies were undertaken in order to evaluate the influence of
time on the formation of f-N-CNT/PTh nanostructures. Polymerization reactions were carried
out for 1 h, 12 h and 24 h and it was found that when the polymerization time increased, the
average diameter of the f-N-CNT/PTh also increased, as did the thickness of the polymer attached onto the f-N-CNTs.
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Kuo, Hsin-Fu, and 郭信甫. "Functionalized Carbon Nanotubes:Surface Decoration and Doping Effect." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/63859799801652308387.
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博士國立清華大學
材料科學工程學系
95
Abstract The works presented in this thesis discuss the effects of non-covalent interaction with carbon nanotubes and molecules as well as Boron-dopants modify electronic structure of carbon nanotubes. Surface decoration has been proved to be important in changing the physico-chemical properties of nanotubes. For example, surface tension, gas sensing and purification via surface reaction are discussed in this study. Doping is well known effective in changing electrical properties of Si-based devices, and it also works in carbon nanotubes. In this study, we demonstrate how bending effect electrical properties in Boron-doped carbon nanotubes (BCNTs) and single-walled carbon nanotubes (SWCNTs). Chapter 1 introduces the basic concept of nanotubes surface decoration by different molecules, e.g. polymers, surfactants, and others chemical species. Two attachments will be discussed, inside and outside the tube, along with the influence of infrared spectroscope analyses. Chapter 2 will discuss the experimental methods, and characterization techniques employed in this study. Chapter 3 shows the ammonia blast on nanotube surface. This work demonstrates the removal of carbonaceous impurities and catalytic particles from carbon nanotube surfaces by ammonia explosion and data reveals that gas sensitivity of purified nanotubes becomes faster by a factor of 3.8 compared with pristine materials. Chapter 4 discusses the observations of surface tension change upon NH3 attachment and droplet (deionized water) migration on nanotube surface. Droplet moving rate, surface tensions of pristine and decorated nanotube films are calculated from experiment information. Feasible mechanism is proposed and influence of droplet migration by external magnetic field is also predicted. Chapter 5 mainly focuses on electron tunneling through boron doped carbon nanotubes. We also show the difference electronic behavior between undoped and B-doped nanotubes. In this chapter, we describe the phenomenon of nanotube deflection driven electron transmission. Chapter 6 concludes results of our experiments.
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Yang, Yi Chang, and 楊益菖. "Effect on Photoelectric Characteristics of Blue Light-Emitting Diodes by Doping in InGaN of GaN/InGaN/GaN." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/68017258889013245799.
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Shu, Chen-Ke, and 徐宸科. "The Characterizations and Studies of Doping and Ion-Implantation Effects in GaN Films." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/21905049296363340543.
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博士國立交通大學
電子物理系
89
The structural and optical properties of impurity doped and P-implanted GaN films were studied by using Raman scattering, photoluminescence, photoluminescence excitation, time-resolved photoluminescence, scanning electronic microscopy, atomic force microscopy, X-ray diffraction, and Hall measurements. The electron concentration reached as high as 1.3x10^19 cm^-3 without cracks or nanopits by using the Si dopant. The solid-vapor ratio was also high about 0.055. The band gap shrinkage of GaN:Si was observed that is proportional to n^{1/3}. In GaN:Mg, we observed the blue-shifts in both X-ray and Raman peaks indicating that Mg dopants possibly replace Ga atoms. The excitation power dependence of photoluminescence were examined. The blue-violet band intensity slowly decreases under continuous wave pumping reflecting the metastable behavior, that may account for the mechanism of the 430 nm peak, and an optical potential barrier of 69 meV was obtained. The isoelectronic In-doping with an adequate TMIn flow rate was found to improve the electrical, crystalline and optical qualities of GaN films. They also show improved surface smoothness with greatly reduced nanopits. More importantly, isoelectronic doping has caused the PL linewidth of the donor-bound exciton emission of GaN to decrease sharply to 10 meV or less at 15 K. The recombination dynamics of GaN:In were also studied by time-resolved photoluminescence. The recombination lifetime decreases sharply to 30 ps, regardless of the measured temperature and the TMIn flow rate that could be related to the intrinsic relaxation channel of the isoelectronic In doping. The P-implantation effects on GaN and the mechanism of yellow luminescence were studied. We also examined the rapid thermal annealing (RTA) effects. The localized states in GaN:P were observed that are different from the step absorption in as-grown GaN. After the RTA processes, the Hall concentration and mobility recovered to the initial values of the as-grown GaN and even slightly better than that. From the Arrhenius plot, the binding energy of the P-iso trap and ionization energy were obatined. For As-doping, we observed that the growth temperature window can be extended to about 900 ℃. The Hall concentration decreased from 3x10^18 to 5x10^17 cm^-3 and the mobility is about 150 cm/V.s. We believed that the proper As-doping indeed helps the electrical properties and crystalline structures. The exciton recombination dynamics were also studied and compared to that of In-doped GaN. The decay time was measured to be temperature dependent and interpreted by the competition between the intrinsic impurity levels and As-induced shallow-acceptor-like levels.