The No-Tillage (NT) diffused in about 70 % of producing grain crops and has emerged as an alternative to soil losses due to the conventional tillage. However, it has been observed in recent years that the basic assumptions of this system are not being considered, reflecting in densification of layers and therefore lower infiltration and soil water storage. Furthermore, due to the characteristics of the system itself, it has been observed the formation of a fertility gradient with high nutrient concentrations in the superficial layers of the soil. With this, the highest goal to be accomplished is to create physical and chemical soil conditions, able to permit greater infiltration and water storage, root growth and absorption capacity of both water and nutrients in depth, depending the vulnerability of soybean and maize recurrent water deficits in the state of RS. The gypsum has been touted as enhancing the chemical characteristics of the subsoil, as his ability to deliver cation and sulphur to lower layers of the listing, in addition to eliminating toxic forms of aluminium to plants. Farmers from the northern region of RS are speculating using this product without observing large returns to grain production, which lacks scientific technical soil and climate in the local conditions. In this sense, this study aimed to verify the effect of gypsum combined with mechanical interventions of a consolidated system of zero tillage on the gradient of cation in the soil profile and the cultivation of soybeans and corn. Application rates of gypsum were performed on the soil surface, with and without mechanical intervention, making it the cultivation of soybeans/corn plants under cover for four seasons (2009/10, 2010/11, 2011/12 and 2012/13). The results showed that the mechanical operations of the soil did not influence the effects of gypsum on the gradient of cations in the soil profile and grain yield of corn and soybeans; Intervention soil with plowing+disking alters the Ca2+ gradient in the soil under NT and the plaster has little potential to mobilize cations vertically soil, and the effects are limited to 0.10 m depth; Use of gypsum shows little maximizing soybean production and maximizing good for corn production, being the contribution of sulfur in soil maximizing main factor. / O Sistema de Plantio Direto (SPD), difundido em cerca de 70% das lavouras produtoras de grãos, surgiu como alternativa conservacionista às perdas de solo por conta do sistema de preparo convencional. No entanto, tem-se observado nos últimos anos que as premissas básicas desse sistema não estão sendo consideradas, repercutindo em adensamento de camadas e consequentemente menor infiltração e armazenamento de água no solo. Além disso, e por conta das características do próprio sistema, tem-se observado a formação de um gradiente de fertilidade com altas concentrações de nutrientes nas camadas superficiais do solo. Com isso, a maior meta a ser cumprida é a de criar condições físico-químicas do solo, capazes de permitirem a maior infiltração e armazenamento de água, o crescimento de raízes e a capacidade de absorção tanto da água quanto dos nutrientes em profundidade, em função da vulnerabilidade das lavouras de soja e milho a déficits hídricos recorrentes no estado do RS. O gesso agrícola tem sido apontado como melhorador das características químicas do subsolo, visto sua capacidade de carrear cátions e enxofre para camadas inferiores do perfil, além de alterar formas tóxicas de alumínio às plantas. Agricultores da região norte do RS estão especulando a utilização deste produto, sem observarem grandes retornos à produção de grãos, que carece de respaldo técnico científico nas condições edafoclimáticas locais. Neste sentido, o presente trabalho teve por objetivo verificar o efeito do gesso agrícola aliado a intervenções mecânicas de um sistema de plantio direto, sobre o gradiente de cátions no perfil do solo e no cultivo de soja e milho. Foram realizada aplicação de doses de gesso agrícola sobre a superfície de solo, com e sem intervenção mecânica, efetuando-se o cultivo da sucessão soja/milho sob plantas de cobertura por quatro safras (2009/10, 2010/11, 2011/12 e 2012/13). Os resultados apontaram que as intervenções mecânicas do solo não influenciam os efeitos do gesso sobre o gradiente de cátions no perfil do solo e as produtividade de grãos do milho e soja; A intervenção do solo com aração+gradagem altera o gradiente de Ca2+ no solo sob SPD e, o gesso tem pouco potencial de mobilizar verticalmente os cátions do solo, sendo que os efeitos são limitados aos 0,10 m de profundidade; O uso do gesso agrícola mostra pouca maximização na produção de soja e boa maximização na produção de milho, sendo o aporte de enxofre no solo o principal fator maximizador.

In this thesis, research on a-Si:H Schottky diodes and a-Si:H/c-Si heterojunctions is presented with the focus on the capacitance spectroscopy and information on electronic properties that can be derived from this technique. Last years a-Si:H/c-Si heterojunctions (HJ) have received growing attention as an approach which combines wafer and thin film technologies due to their low material consumption and low temperature processing. HJ solar cells benefit from lower fabrication temperatures thus reduced costs, possibilities of large-scale deposition, better temperature coefficient and lower silicon consumption. The most recent record efficiency belongs to Panasonic with 24.7% for a cell of 100 cm² was obtained. The aim of this thesis is to provide a critical study of the capacitance spectroscopy as a technique that can provide information on both subjects: DOS in a-Si:H and band offset values in a-Si:H/c-Si heterojunctions.The first part of the manuscript is devoted to capacitance spectroscopy in a-Si:H Schottky diodes. The interest is concentrated on the simplified treatment of the temperature and frequency dependence of the capacitance that allows one to extract the density of states at the Fermi level in a-Si:H. We focus on the study of the reliability and validity of this approach applied to a-Si:H Schottky barriers with various magnitudes and shapes of the DOS. Several structures representing n-type and undoped hydrogenated amorphous silicon Schottky diodes are modeled with the help of numerical simulation softwares. We show that the reliability of the studied treatment drastically depends on the approximations used to obtain the explicit analytical expression of the capacitance in such an amorphous semiconductor.In the second part of the chapter, we study the possibility of fitting experimental capacitance data by numerical calculations with the input a-Si:H parameters obtained from other experimental techniques. We conclude that the simplified treatment of the experimentally obtained capacitance data together with numerical modeling can be a valuable tool to assess some important parameters of the material if one considers the results of numerical modeling and performs some adjustments. The second part is dedicated to capacitance spectroscopy of a-Si:H/c-Si heterojunctions with special emphasis on the influence of a strong inversion layer in c-Si at the interface. Firstly, we focus on the study of the frequency dependent low temperature range of capacitance-temperature dependencies of a-Si:H/c-Si heterojunctions. The theoretical analysis of the capacitance steps in calculated capacitance-temperature dependencies is presented by means of numerical modeling. It is shown that two steps can occur in the low temperature range, one being attributed to the activation of the response of the gap states in a-Si:H to the small signal modulation, the other one being related to the response of holes in the strong inversion layer in c-Si at the interface. The experimental behavior of C-T curves is discussed. The quasi-static regime of the capacitance is studied as well. We show that the depletion approximation fails to reproduce the experimental data obtained for (p) a-Si:H/(n) c-Si heterojunctions. Due to the existence of the strong inversion layer, the depletion approximation overestimates the potential drop in the depleted region in crystalline silicon and thus underestimates the capacitance and its increase with temperature. A complete analytical calculation of the heterojunction capacitance taking into account the hole inversion layer is developed. It is shown that within the complete analytical approach the inversion layer brings significant changes to the capacitance for large values of the valence band offset. The experimentally obtained C-T curves show a good agreement with the complete analytical calculation and the presence of the inversion layer in the studied samples is thus confirmed.

Les travaux développés dans cette thèse sont dédiés à l’étude des propriétés électroniques de diodes Schottky de silicium amorphe hydrogéné (a-Si:H) et d'hétérojonctions entre silicium amorphe hydrogéné et silicium cristallin, a-Si:H/c-Si au moyen de spectroscopies de capacité de jonctions.Lors de la fabrication des cellules solaires à haut rendement plusieurs paramètres d’une hétérojonction a-Si:H/c-Si doivent être considérés. Premièrement, la densité d’états dans le gap du a-Si:H est d’une grande importance car il s’agit de défauts qui favorisent le piégeage et la recombinaison de porteurs. Deuxièmement, la détermination des désaccords des bandes entre la couche amorphe et la couche cristalline est indispensable puisque ceux-ci contrôlent le transport à travers la jonction et déterminent la courbure des bandes dans c-Si, ce qui va notamment influencer la recombinaison des porteurs sous lumière, donc la tension de circuit ouvert des cellules. Cette thèse a pour but d’étudier la spectroscopie de capacité comme technique d'analyse de paramètres clés pour les dispositifs à hétérojonctions de silicium : la densité d’états dans le a-Si:H et les désaccords des bandes entre a-Si:H et c-Si.La première partie est dédiée à l’étude de la capacité de diodes Schottky. Nous nous concentrons sur un traitement simplifié de la capacité en fonction de la température et de la fréquence reposant sur une expression analytique obtenue par une résolution approchée de l'équation de Poisson. Ce traitement permet en principe d’extraire la densité d’états au niveau de Fermi dans le a-Si:H et la fréquence de saut des électrons depuis un état localisé au niveau de Fermi vers la bande de conduction. En appliquant ce traitement simplifié à la capacité calculée sans approximation à l'aide de deux logiciels de simulation numérique, nous montrons que sa fiabilité et sa validité dépendent fortement de la distribution des états localisés dans la bande interdite du a-Si:H et de la position du niveau de Fermi. Puis nous abordons l’étude de la capacité des hétérojonctions entre a-Si:H de type p et c-Si de type n, et nous mettons particulièrement en avant l’existence d'une couche d’inversion forte à l’interface dans le c-Si, formant un gaz bidimensionnel de trous. Dans une première partie, nous présentons une étude par simulation numérique de la dépendance de la capacité en fonction de la température, pour laquelle un ou deux échelons peuvent être mis en évidence à basse température. Leur analyse montre qu’un des ces échelons est attribué à l’activation de la réponse de la charge dans le a-Si:H, alors que l’autre, présentant une énergie d'activation plus grande, est lié à la modulation de la concentration des trous dans la couche d’inversion forte, lorsque celle-ci existe. On présente ensuite une discussion de résultats expérimentaux. Le régime quasi-statique de la capacité fait ainsi l’objet d’une discussion. Nous mettons en relief le fait que l’approximation de la zone de déplétion ne permet pas de reproduire cette augmentation de la capacité en fonction de la température. Du fait de l’existence de la couche d’inversion forte, la chute de potentiel dans la zone de déplétion du c-Si est plus faible que la valeur déterminée par le calcul attribuant toute la chute de potentiel à la zone de déplétion. Par conséquent, cette approximation conduit à sous-estimer la capacité ainsi que son augmentation avec la température. Nous présentons alors un calcul analytique complet qui tient compte à la fois de la distribution particulière du potentiel dans le a-Si:H, et des trous dans le c-Si dont la contribution à la concentration totale de charges n'est pas négligeable dans la couche d’inversion forte. Le calcul analytique complet permet de bien reproduire les résultats expérimentaux de capacité en fonction de la température; ceci confirme la présence de la couche d’inversion forte dans les échantillons étudiés. / In this thesis, research on a-Si:H Schottky diodes and a-Si:H/c-Si heterojunctions is presented with the focus on the capacitance spectroscopy and information on electronic properties that can be derived from this technique. Last years a-Si:H/c-Si heterojunctions (HJ) have received growing attention as an approach which combines wafer and thin film technologies due to their low material consumption and low temperature processing. HJ solar cells benefit from lower fabrication temperatures thus reduced costs, possibilities of large-scale deposition, better temperature coefficient and lower silicon consumption. The most recent record efficiency belongs to Panasonic with 24.7% for a cell of 100 cm² was obtained. The aim of this thesis is to provide a critical study of the capacitance spectroscopy as a technique that can provide information on both subjects: DOS in a-Si:H and band offset values in a-Si:H/c-Si heterojunctions.The first part of the manuscript is devoted to capacitance spectroscopy in a-Si:H Schottky diodes. The interest is concentrated on the simplified treatment of the temperature and frequency dependence of the capacitance that allows one to extract the density of states at the Fermi level in a-Si:H. We focus on the study of the reliability and validity of this approach applied to a-Si:H Schottky barriers with various magnitudes and shapes of the DOS. Several structures representing n-type and undoped hydrogenated amorphous silicon Schottky diodes are modeled with the help of numerical simulation softwares. We show that the reliability of the studied treatment drastically depends on the approximations used to obtain the explicit analytical expression of the capacitance in such an amorphous semiconductor.In the second part of the chapter, we study the possibility of fitting experimental capacitance data by numerical calculations with the input a-Si:H parameters obtained from other experimental techniques. We conclude that the simplified treatment of the experimentally obtained capacitance data together with numerical modeling can be a valuable tool to assess some important parameters of the material if one considers the results of numerical modeling and performs some adjustments. The second part is dedicated to capacitance spectroscopy of a-Si:H/c-Si heterojunctions with special emphasis on the influence of a strong inversion layer in c-Si at the interface. Firstly, we focus on the study of the frequency dependent low temperature range of capacitance-temperature dependencies of a-Si:H/c-Si heterojunctions. The theoretical analysis of the capacitance steps in calculated capacitance-temperature dependencies is presented by means of numerical modeling. It is shown that two steps can occur in the low temperature range, one being attributed to the activation of the response of the gap states in a-Si:H to the small signal modulation, the other one being related to the response of holes in the strong inversion layer in c-Si at the interface. The experimental behavior of C-T curves is discussed. The quasi-static regime of the capacitance is studied as well. We show that the depletion approximation fails to reproduce the experimental data obtained for (p) a-Si:H/(n) c-Si heterojunctions. Due to the existence of the strong inversion layer, the depletion approximation overestimates the potential drop in the depleted region in crystalline silicon and thus underestimates the capacitance and its increase with temperature. A complete analytical calculation of the heterojunction capacitance taking into account the hole inversion layer is developed. It is shown that within the complete analytical approach the inversion layer brings significant changes to the capacitance for large values of the valence band offset. The experimentally obtained C-T curves show a good agreement with the complete analytical calculation and the presence of the inversion layer in the studied samples is thus confirmed.

In this thesis, research on a-Si:H Schottky diodes and a-Si:H/c-Si heterojunctions is presented with the focus on the capacitance spectroscopy and information on electronic properties that can be derived from this technique. Last years a-Si:H/c-Si heterojunctions (HJ) have received growing attention as an approach which combines wafer and thin film technologies due to their low material consumption and low temperature processing. HJ solar cells benefit from lower fabrication temperatures thus reduced costs, possibilities of large-scale deposition, better temperature coefficient and lower silicon consumption. The most recent record efficiency belongs to Panasonic with 24.7% for a cell of 100 cm² was obtained. The aim of this thesis is to provide a critical study of the capacitance spectroscopy as a technique that can provide information on both subjects: DOS in a-Si:H and band offset values in a-Si:H/c-Si heterojunctions.The first part of the manuscript is devoted to capacitance spectroscopy in a-Si:H Schottky diodes. The interest is concentrated on the simplified treatment of the temperature and frequency dependence of the capacitance that allows one to extract the density of states at the Fermi level in a-Si:H. We focus on the study of the reliability and validity of this approach applied to a-Si:H Schottky barriers with various magnitudes and shapes of the DOS. Several structures representing n-type and undoped hydrogenated amorphous silicon Schottky diodes are modeled with the help of numerical simulation softwares. We show that the reliability of the studied treatment drastically depends on the approximations used to obtain the explicit analytical expression of the capacitance in such an amorphous semiconductor.In the second part of the chapter, we study the possibility of fitting experimental capacitance data by numerical calculations with the input a-Si:H parameters obtained from other experimental techniques. We conclude that the simplified treatment of the experimentally obtained capacitance data together with numerical modeling can be a valuable tool to assess some important parameters of the material if one considers the results of numerical modeling and performs some adjustments. The second part is dedicated to capacitance spectroscopy of a-Si:H/c-Si heterojunctions with special emphasis on the influence of a strong inversion layer in c-Si at the interface. Firstly, we focus on the study of the frequency dependent low temperature range of capacitance-temperature dependencies of a-Si:H/c-Si heterojunctions. The theoretical analysis of the capacitance steps in calculated capacitance-temperature dependencies is presented by means of numerical modeling. It is shown that two steps can occur in the low temperature range, one being attributed to the activation of the response of the gap states in a-Si:H to the small signal modulation, the other one being related to the response of holes in the strong inversion layer in c-Si at the interface. The experimental behavior of C-T curves is discussed. The quasi-static regime of the capacitance is studied as well. We show that the depletion approximation fails to reproduce the experimental data obtained for (p) a-Si:H/(n) c-Si heterojunctions. Due to the existence of the strong inversion layer, the depletion approximation overestimates the potential drop in the depleted region in crystalline silicon and thus underestimates the capacitance and its increase with temperature. A complete analytical calculation of the heterojunction capacitance taking into account the hole inversion layer is developed. It is shown that within the complete analytical approach the inversion layer brings significant changes to the capacitance for large values of the valence band offset. The experimentally obtained C-T curves show a good agreement with the complete analytical calculation and the presence of the inversion layer in the studied samples is thus confirmed.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21579号 / 理博第4486号 / 新制||理||1644(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 橋口 浩之, 教授 塩谷 雅人, 教授 秋友 和典 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

En 2003 des mesures au spectromètre IR à Transformée de Fourier (FTIR) ont permis d'identifier et de mesurer les COV émis par la décharge à ciel ouvert de la Gabarre, principale de l'île Guadeloupe, située entre une zone urbaine et une mangrove. Ces COV ont été retrouvés (2004) la nuit dans les cités, justifiant les plaintes des riverains. Dans le cadre de cette thèse, des mesures au spectromètre de masse portatif MS 200 ont validé ces résultats du FTIR. De nouvelles mesures au MS 200 ont été menées dans toute la zone de la décharge. Les cités concernées étant à l'opposé du flux synoptique d'Alizés-Est, les facteurs météorologiques permettant la dispersion et le transport des COV de la décharge vers la zone urbaine ont été recherchés. La diminution nocturne de l'intensité des Alizés au dessus de l'ile peut laisser place à des phénomènes locaux tels les brises. L'idée d'une brise terre-mer a été éliminée. Un maillage autou~ de la décharge (cités et mangrove) avec 8 thermomètres a révélé un îlot de chaleur urbain nocturnegénérant une brise thermique d'environ Ims- I (mesurée et calculée). Avec les radiosondages Météo France et un SODAR installé dans la décharge, une très forte stabilité dans les basses couches atmosphériques de la couche limite nocturne avec une inversion de surface d'environ 120mvv apparait. Ces facteurs expliquent la pollution des cités par les COV de la décharge, Un modèlevGaussien en tenant compte a été validé par les mesures de COV.vCette étude peut être étendue à d'autres décharges à ciel ouvert et à d'autres types de traitement de polluants de décharge. / In 2003, the VOC emissions coming from "La Gabarre", the main open landfill in Guadeloupe, located in-between an urban area and a mangrove, were identified and quantified with a portable FTIR spectrometer. In 2004, COVs found at nighttime in the urban area nearby confirmed why residents complain about. As part of this thesis, portable mass spectrometer MS 200 measurements validated these FTIR figures. New systematic SM measurements have been carried on around the landfill. Since the polluted urban area stands on the opposite way of the East Trade winds synoptic flux, aIl the weather factors likely to scatter and transport the dump COVs were scrutinized. At night, the strength of the Trade winds decreases over Guadeloupe, which may give way to local phenomena such as breezes. The occurrence of land/sea breeze was eliminated. A close surveying surrounding the landfill with 8 thermometers both in the projects and in the mangrove revealed an urban heat island causing thermal breezes of about lms-l (measured and calculated). Using soundings from Meteo France, and a SODAR inside the dump, we found a great stability of the night boundary layer with a surface inversion near 120m. Pollution of the nearby urban area with landfill COVs is elucidatcd by the above factors. A transport Gaussian model is in agreement with COV measurements. This study can be extended to different open landfills and different types of polluting matters processes in dumps

Le rendement consommation/fréquence des futures générations de circuits intégrés sur silicium n’est pas satisfaisant à cause de la faible mobilité électronique de ce semi-conducteur et des relativement grandes tensions d’alimentation VDD requises. Ce travail se propose d’explorer numériquement les potentialités des transistors à effet de champ (FET) à base de matériaux III-V à faible bande interdite et à haute mobilité pour un fonctionnement en haute fréquence et une ultra basse consommation. Tout d’abord, l’étude consiste à analyser théoriquement le fonctionnement d’une capacité MOS III-V en résolvant de façon auto-cohérente les équations de Poisson et Schrödinger (PS). On peut ainsi comprendre comment et pourquoi les effets extrinsèques comme les états de pièges à l’interface high-k/III-V dégradent les caractéristiques intrinsèques. Pour une géométrie 2D, les performances des dispositifs sont estimées pour des applications logiques et analogiques à l’aide d’un modèle de transport quasi-balistique.Nous avons ensuite étudié plus en détails les performances des MOSFET III-V en régimes statiques et dynamiques sous faible VDD, à l’aide du simulateur particulaire MONACO de type Monte Carlo. Les caractéristiques de quatre topologies de MOSFET ont été quantitativement étudiées, en termes de transport quasi-balistique, de courants statiques aux états passants et bloqués, de rendement fréquence/consommation et de bruit. Nous en tirons des conclusions sur l’optimisation de ces dispositifs. Enfin, l'étude comparative avec un FET à base de Si démontre clairement le potentiel des MOSFET III-V pour les applications à haute fréquence, à faible puissance de consommation et à faible bruit. / The optimal frequency performance/power-consumption trade-off is very difficult to achieve using CMOS technology because of low Si carrier mobility and relatively large supply voltage (VDD) required for circuit operation. The main objective of this work is to theoretically explore, in terms of operation frequency and power consumption, the potentialities of nano-MOSFET based on III-V materials with low energy bandgap and high electron mobility.First, this work analyzes theoretically the operation of a III-V MOS capacitor using self-consistent solution of Poisson - Schrödinger system equation. We can thus understand how and why the interface trap state densities at high-k/III-V interfaces degrade the intrinsic characteristics. For a 2D geometry, the performance of devices is estimated for digital and analog applications using a model of quasi-ballistic transport.Then, we estimated the performance of III-V MOSFET in static and dynamic regimes under low VDD, using MONACO a Monte Carlo simulator. The characteristics of four designs of III-V MOSFET have been studied quantitatively in terms of quasi-ballistic transport, DC current in ON and OFF states, frequency/consumption efficiency and optimum matching conditions of noise. We provide the guideline on the design optimization of the devices.Finally, the comparative study with Si-based devices clearly demonstrates the potentiality of III-V nano-MOSFET architectures for high-frequency and low-noise application under low operating power and even for low voltage logic.