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

Electric force microscopy techniques on GaAs mesoscopic structures / Técnicas de microscopia de força elétrica em estruturas mesoscópicas de GaAs

Lanzoni, Evandro Martin 29 March 2018 (has links)
Submitted by Evandro Martin Lanzoni (evandrolanzoni@yahoo.com.br) on 2018-05-28T18:03:48Z No. of bitstreams: 1 dissertação mestrado evandro lanzoni_versão final.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) / Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2018-05-28T19:02:57Z (GMT) No. of bitstreams: 1 lanzoni_em_me_bauru.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) / Made available in DSpace on 2018-05-28T19:02:57Z (GMT). No. of bitstreams: 1 lanzoni_em_me_bauru.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) Previous issue date: 2018-03-29 / As técnicas de microscopia de sonda Kelvin (KPFM) e de microscopia de força eletrostática (EFM) são amplamente utilizadas para analisar a distribuição do potencial de superfície, porém com pouca aplicação em nanoestruturas semicondutoras auto-organizadas embutidas em um substrato. Neste trabalho, investigamos diretamente o acúmulo de carga dentro de estruturas mesoscópicas de GaAs (MGS) [1]. As estruturas são fabricadas através do crescimento sobreposto de um modelo de nano orifícios usando epitaxia de feixe molecular. Para tal, uma combinação de desoxidação assistida por Ga e ataque químico por gotículas localizadas foram utilizadas para criar orifícios iniciais com uma profundidade de ca. 10 a 15nm, que são posteriormente cobertos com 15nm de barreira AlxGax-1As e GaAs com 1nm, 2nm, 5nm, 10nm de espessura. Microscopia de força atômica e microscopia eletrônica de transmissão mostraram que a forma do orifício é preservada durante o crescimento de AlGaAs. Em seguida, esses orifícios são preenchidos com GaAs formando uma estrutura alongada sobre o buraco [1]. Investigamos o potencial de superfície local e a distribuição das cargas nestas estruturas com a técnica KPFM de passagem única. Portanto, uma voltagem AC de 5 V é aplicada a uma ponta metalizada e varremos a amostra no modo de contato intermitente. Observamos uma clara diferença de potencial na região central da estrutura, onde esperamos o furo preenchido. Então, um estudo sistemático com a técnica de KPFM mostrou a influência no acúmulo de carga quando a espessura de GaAs é alterada, bem como, quando modificamos a concentração de Al na barreira de AlGaAs. O cálculo simulando um poço de potencial com barreiras semi-finitas e finitas mostrou que não ocorre acúmulo de carga quando a espessura do GaAs é menor que 1,5 nm, corroborando com nossos resultados. Simulações do diagrama de banda e da densidade de elétron da estrutura permitem atribuir o acumulo de carga observado, aos diferentes níveis de energia da estrutura mesoscópica de GaAs em comparação com as camadas de GaAs circundantes. / Kelvin probe force microscopy and electric force microscopy techniques are widely used to analyze the distribution of the surface potential with little application to self-assembled semiconductor nanostructures embedded into a substrate. In this work, we directly investigate the charge accumulation inside mesoscopic GaAs structures [1]. The structures are fabricated by overgrowth of a nanohole template using molecular beam epitaxy. Therefore, a combination of Ga assisted deoxidation and local droplet etching is used to create initial holes with a depth of ca. 10 to 15nm, which are covered subsequently with 15nm of AlxGax-1As barrier and GaAs caps with 1nm, 2nm, 5nm, 10nm thicknesses. Atomic force microscopy and transmission electron microscopy results showed that the hole shape is preserved during the AlGaAs overgrowth. Then filled with GaAs forming an elongated mount over the hole [1]. We investigate the local potential and the charge distribution in these structures with a single pass Kelvin probe force microscopy technique. Therefore, an AC voltage of 5 V is applied to a metalized tip and scanned in tapping mode over the sample. We observed a clear potential difference in Kelvin probe force microscopy measurements in the middle of the structure, where we expect a filled hole. We systematically study by Kelvin probe force microscopy the influence on the charge accumulation when the GaAs thickness is changed, as well as the Al concentration in the AlGaAs barrier. Calculation of the particle in the box for semi-finite and finite barriers were done and show that no charge accumulation is observed for GaAs thickness lower than 1.5nm in the semi-finite barrier, corroborating with our results. Simulations of band gap and electron wavefunction of the structure allow us to ascribe the charge accumulation observed, to the different confinement of carriers inside of the unstrained mesoscopic GaAs structure compared to the surrounding GaAs layers.
2

Stínící efekt oxidové izolační vrstvy na povrchový potenciál měřený pomocí Kelvinovy sondové mikroskopie / Shielding Effect of Oxide Isolating Layer on Surface Potential Measured by Kelvin Probe Force Microscopy

Švarc, Vojtěch January 2015 (has links)
The diploma thesis deals with the experimental study of shielding effect of oxide isolating layer on surface potential measured by Kelvin Probe Force Microscopy. For the study of surface potential were created Au/SiO2 based nanostructures by Electron Beam Lithography, Atomic Layer Deposition and Multilayer Deposition. Surface potential was measured depending on the relative humidity and thickness of oxide isolating layer.
3

Time-Resolved Kelvin Probe Force Microscopy of Nanostructured Devices

Murawski, Jan 29 May 2017 (has links) (PDF)
Since its inception a quarter of a century ago, Kelvin probe force microscopy (KPFM) has enabled studying contact potential differences (CPDs) on the nanometre scale. However, current KPFM investigations are limited by the bandwidth of its constituent electronic loops to the millisecond regime. To overcome this limitation, pump-probe-driven Kelvin probe force microscopy (pp-KPFM) is introduced that exploits the non-linear electric interaction between tip and sample. The time resolution surpasses the electronic bandwidth and is limited by the length of the probe pulse. In this work, probe pulse lengths as small as 4.5 ns have been realized. These probe pulses can be synchronized to any kind of pump pulses. The first system investigated with pp-KPFM is an electrically-driven organic field-effect transistor (OFET). Here, charge carrier propagation in the OFET channel upon switching the drain-source voltage is directly observed and compared to simulations based on a transmission line model. Varying the charge carrier density reveals the impeding influence of Schottky barriers on the maximum switching frequency. The second system is an optically-modulated silicon homojunction. Here, the speed of surface photovoltage (SPV) build-up is accessed and compared to timeaveraged results. Due to slow trap states, the time-averaged method is found to lack comprehensiveness. In contrast, pp-KPFM exposes two intensity-dependent recombination times on the same timescale — high-level Shockley-Read-Hall recombination in the bulk and heat-dominated recombination in the surface layer — and a delay of the SPV decay with rising frequency, which is attributed to charge carrier retention at nanocrystals. The third system is a DCV5T-Me:C60 bulk heterojunction. The SPV dynamics is probed and compared to measurements via open-circuit corrected transient charge carrier extraction by linearly increasing voltage. Both methods reveal an exponential onset of the band bending reduction that is attributed to the charge carrier diffusion time in DCV5T-Me, and a double exponential decay, hinting at different recombination paths in the studied organic solar cell. The above-mentioned experiments demonstrate that pp-KPFM surpasses conventional KPFM when it comes to extracting dynamic device parameters such as charge carrier retention and recombination times, and prove that pp-KPFM is a versatile and reliable tool for studying electrodynamics on nanosurfaces.
4

Modeling and physical studies of kesterite solar cells

Cozza, Dario 28 January 2016 (has links)
Ce travail de thèse porte sur la modélisation et la simulation numérique de cellules solaires à base de kësterite (CZTSé, CZTS) dans le but d’étudier leurs mécanismes physiques et d’améliorer la conception de ces dispositifs. Les kësterites sont une classe de matériaux que l’on peut déposer en couches minces et qui sont constitués d’éléments abondants sur Terre et donc à faible coût. Deux modèles numériques pour les cellules solaires CZTSe et CZTS sont proposés. Des simulations 1D et 2D sont réalisées: le logiciel SCAPS est utilisé pour étudier l’impact des couches de molybdène et de MoSe2, présents au contact arrière des cellules solaires CZTSe. Nous étudions également les propriétés idéales de couches d’interface alternatives qui pourraient remplacer le MoSe2 pour améliorer les performances des cellules solaires. La méthode des matrices de transfert (TMM) et le logiciel SCAPS sont utilisés conjointement pour effectuer des simulations optoélectroniques dans le but d’optimiser l’épaisseur du buffer (CdS) et le TCO (Transparent Conductive Oxide) afin de maximiser le courant de court-circuit (JSC ) des cellules solaires. Enfin Silvaco est utilisé pour réaliser des simulations 2D des joints de grains (GBs) du CZTSe présents à l’intérieur des absorbeurs polycristallins de la kësterite. Pour ce faire, des caractérisations KPFM sont effectuées dans le but de trouver des corrélations possibles entre les pertes de rendement et l'activité électrique des GBs. / This thesis deals with modeling and simulations of kesterite solar cells with the aim of studying their physical mechanisms and improving the design of the devices. Synthetic kesterites are thin film materials made of cheap/earth-abundant elements. Two numerical models for a Cu2ZnSnSe4 (CZTSe) and a Cu2ZnSnS4 (CZTS) solar cell are proposed. The provided values of the material parameters, for all the layers of the solar cell, are obtained either from comparisons/analysis of data found in literature or, in some cases, from direct measurements. 1D and 2D simulations are performed: the software SCAPS is used to study the impact of the Molybdenum and the MoSe2 layers, present at the back contact of CZTSe solar cells. We investigate also the ideal properties of alternative interfacial layers that could replace the MoSe2 layer to improve the device performances. The transfer matrix method (TMM) and SCAPS are employed together to perform optoelectronic simulations with the aim of optimizing the thickness of the buffer (CdS) and the window (ITO) layers in order to maximize the short circuit current (JSC ) of the device. Finally Silvaco is used to perform 2D simulations of the CZTSe grain boundaries (GBs) present inside the polycrystalline kesterite absorbers. For the latter work, experimental Kelvin probe force microscopy (KPFM) characterizations are performed in order to find possible correlations between the performance losses and the electrical activity of the GBs.
5

Etude des processus physiques à l'interface isolant-polymère semiconducteur / Investigation of physical process at polymer insulation-conductive filler interface

Gullo, Francesco 25 April 2018 (has links)
Une des propriétés fondamentales des diélectriques est d'accumuler des charges sous l'effet d'un champ électrique. Si cet effet est exploité dans certaines applications telles que les mémoires il est la plupart du temps la cause de défaillance dans de nombreux systèmes tels que les câbles haute tension ou les microsystèmes. De nombreuses études ont démontré que l'interface entre le diélectrique et l'électrode jouait un rôle prédominant dans le fonctionnement du système complet et en particulier influençait le phénomène d'injection de charge à l'origine des défaillances. Au cours des dernières années le phénomène d'injection de charges à l'interface électrode/diélectrique a largement été étudié. Pour expliquer la différence entre les résultats expérimentaux et les modèles, l'hypothèse la plus plausible est la présence d'états d'interfaces entre l'électrode (métal ou semiconducteur) et le diélectrique. Cette hypothèse permet en particulier d'expliquer l'indépendance de la quantité de charge injectée vis-à-vis du métal servant d'électrode. Toutefois, les propriétés des interfaces restent mal connues en particulier car ces phénomènes nanométriques sont caractérisés à partir de mesures microscopique. L'objectif de cette thèse est de caractériser les propriétés chimiques et électriques de l'interface grâce à un contrôle rigoureux de son procédé de fabrication. L'apport majeur de ces travaux est lié à l'utilisation de la microscopie à force atomique pour déterminer les propriétés de l'interface à l'échelle nanométrique. Nous avons en particulier caractérisé morphologiquement (mesure de propriétés mécaniques par PFQNM - Peak Force Quantitative NanoMechanical) et électriquement (mesure de potentiel de surface par KPFM - Kelvin Probe Force Microscopy). Nous avons ainsi pu montrer que le procédé de fabrication influençait les propriétés chimiques (oxydation de surface...) de l'interface sans que cela ait de conséquences notables sur les propriétés électriques. En effet, la quantité de charges injectées reste du même ordre de grandeur quel que soit le procédé de fabrication. Les mesures AFM ont montré que l'interface morphologique était abrupte alors que l'interface électrique était progressive (plusieurs microns). Grâce à un modèle nous avons pu extraire des mesures de potentiel de surface KPFM la densité de charge d'interface. / One of the fundamental properties of dielectrics is to accumulate charges under an electric field. Even if this phenomena is exploited in some applications such as memories, it is the main cause of failure in a large amount of applications such as high voltage cables or microsystems. Numerous studies have demonstrated that dielectric/electrode interface has strong impact on complete system and particularly on charge injection phenomenon which induce failures. During the past decades, charge injection phenomena electrode / dielectric interface has been extensively studied. To explain the difference between experimental and modelling, the most plausible hypothesis is the presence of interface states between the electrode (metal or semiconductor) and the dielectric. This hypothesis explain the independence of injected charge density respect to the electrode meta (work function). However, interfaces properties remain poorly understood mainly because all nanometric phenomena accuring at its localization are characterized thanks to microscopic measurements. The aim of this PhD thesis is to characterize chemical and electrical properties of the interface through a rigorous control of its manufacturing process. The major contribution of this work is related to the use of Atomic Force Microscopy (AFM) to determine interface properties at nanoscale. In particular, interfaces are characterized morphologically (mechanical properties measurements by PFQNM - Peak Quantitative Quantum NanoMechanical) and electrically (surface potential measurements by KPFM - Kelvin Probe Force Microscopy). Thus, results demonstrate that the manufacturing process influenced the chemical properties (surface oxidation ...) of the interface without having any significant influence on the electrical properties. Indeed, the amount of injected charges remains quite the same regardless of the manufacturing process. AFM measurements showed that the morphological interface was abrupt whereas the electrical interface was progressive (several microns). A Matlab model permits us to extract interface charge density to KPFM surface potential measurements.
6

Etude des mécanismes d'injection et de stockage de charges électriques dans un film mince diélectrique par microscopie à sonde de Kelvin (KPFM) / Study of injection and trapping mechanisms of electrical charges in thin dielectric films by Kelvin probe force microscopy (KPFM)

Mortreuil, Florian 13 November 2015 (has links)
Une des propriétés intrinsèques des matériaux diélectriques est d'accumuler des charges électriques sous l'action de contraintes extérieures (température, champ électrique...). Ce phénomène utile dans certaines applications (mémoires non volatiles...), demeure en général une cause de défaillance (microsystèmes...). Il convient donc de disposer d'une méthode permettant de mesurer cette densité de charges aux échelles pertinentes pour le système. Du fait de la miniaturisation, les méthodes classiques de mesure de charge d'espace (PEA, FLIMM,...) ne sont plus adaptées, car leurs résolutions latérales de quelques micromètres est bien supérieure aux dimensions nanométriques des systèmes. Une nouvelle méthode de mesure de la charge d'espace basée sur la microscopie à champ proche, et plus particulièrement la mesure de potentiel de surface par microscopie à sonde de Kelvin (KPFM), permet d'obtenir des informations sur l'état de charge du matériau avec une résolution nanométrique. Notre objectif est d'étudier les phénomènes d'injection et de rétention de charges dans des diélectriques minces. Pour cela deux voies ont été explorées. La première consiste à injecter localement des charges à la surface d'une couche mince de SiOxNy d'épaisseur variable (entre 6nm et 130nm) et à mesurer les modifications du potentiel de surface induit par les charges. Les mesures de potentiel de surface (KPFM) et de courant (C-AFM) couplées à des simulations du champ électrique par éléments finis (COMSOL) ont mis en évidence que deux mécanismes sont en jeu lors de l'injection de charges : le piégeage dans la couche et la conduction au travers de la couche. Pour les épaisseurs les plus fines la conduction est le mécanisme majoritaire (ce qui limite la quantité de charges piégées) alors que pour les films plus épais le piégeage est majoritaire. Pour les films d'épaisseur intermédiaire les deux mécanismes sont en compétition. Une fois les charges injectées leur dissipation se fait majoritairement dans le volume selon une dynamique indépendante de l'épaisseur de la couche. La seconde voie consiste à étudier l'injection et le déplacement de charges entre deux électrodes latérales enfouies dans le diélectrique. Cette structure permet de s'affranchir du manque de sensibilité de la mesure KPFM à la profondeur des charges dans le volume et d'étudier les phénomènes d'injection aux interfaces et le transport de charges sous champ électrique. Le champ électrique induit entre les deux électrodes polarisées a été simulé par éléments finis sous COMSOL et comparé aux mesures de potentiel KPFM. Nous avons ainsi pu caractériser l'injection à l'interface métal/diélectrique et nous avons montré la faisabilité d'utiliser ce type de structure pour étudier la mobilité des charges au sein d'une couche diélectrique. / One of the intrinsic properties of dielectrics is to accumulate electrical charges when subjected to external stresses (temperature, electrical field ...). This property can be helpful for some applications (DRAM...), but leads generally to failure of the device (micro-system...). Thus, a charge density measurement technics is mandatory for the scale of relevance according to the observed system. However due to miniaturization, the measurement technics classically used are helpless to study tiny systems of a few tens nanometers thick, as their spatial resolution is of the order a few micrometers. A new measurement technics represented by KPFM (Kelvin Probe Microscopy) and based on near field microscopy technology, can measure charges on a material with nanoscale lateral resolution. Our purpose here is to characterize charges injection and decay mechanisms in thin SiOxNy and SiNx film deposited by plasma process, thanks to near field microscopy. To achieve this goal, two approaches have been explored. The first one consists in localized injection of electrical charges at the surface of a thin SiOxNy layer of variable thickness (between 6 nm and 130nm) and to measure surface potential modification induced by injected charges. Surface potential (KPFM) and current (C-AFM) measurements coupled to electric field simulation by finite element (COMSOL(r)) emphasizes that two mechanisms are involved during charges injection: trapping and conduction through the layer. For thinner layers, conduction mechanism is predominant (which limits trapped charges amount); while for thicker films trapping is the main mechanism. For intermediate thickness films both mechanisms are in competition. Once the charges injected, dissipation in volume appears to be the predominant mechanism for any thickness. The second approach is the study of charges injection and transport between two embedded lateral electrodes. This structure allows overcoming the lack of in-depth sensitivity of the KPFM measurement toward the position of charges in the volume, to study injection phenomena at interfaces and transport of charges within the volume under electrical field constraint. The electric field induced between the two polarized electrodes was simulated by finite element using COMSOL and compared to surface potential measured by KFM. Results emphasize technical issues related to charges injection/transport between lateral electrodes. According to this analysis an experimental set up and data post-treatment protocol is developed which permits to characterized charges injection at interface. Besides, feasibility of charges mobility investigation using this type of structure was demonstrated.
7

Développement d’une méthode de mesure du potentiel de surface par AFM pour composants électroniques en fonctionnement, application aux transistors organiques / Surface potential measurements of biased devices using Kelvin force probe microscopy applied to thin film organic transistors

De tournadre, Grégoire 28 June 2016 (has links)
Au cours de cette thèse, une technique de mesure du potentiel de surface par AFM (KPFM) a été développée et exploitée. Elle permet la caractérisation locale et quantitative de transistors organiques (OTFT) polarisés à plusieurs dizaines de volts, en condition ambiante. Cependant tout type de composants polarisés dont la surface est accessible peut être étudié. La méthode a été utilisée de façon complémentaire à l’étude conventionnelle des caractéristiques courant-tension des transistors et à la simulation, elle contribue ainsi à une meilleure compréhension des mécanismes de transport et d’injection des porteurs dans les OTFT. Nous avons étudié des transistors en structure empilée ou planaire et à base de semi-conducteurs variés (PTAA, DNTT, P3HT). Nous avons obtenu des caractéristiques courant-tension intrinsèques du contact de source, ohmique ou non-linéaire, suivant les cas. Les résultats sont 10 fois plus précis qu’avec la méthode dite « transmission line method (TLM) » et permettent d’étudier chaque transistor individuellement. La modélisation des contacts s’est appuyée sur l’implémentation du modèle d’injection d’Arkhipov dans un simulateur quasi-2D. Une nouvelle méthode de mesure de la mobilité et de la tension de seuil à partir des profils de potentiel a été introduite. Nous avons ainsi mesuré la mobilité du canal indépendamment des effets des contacts. Etonnamment la mobilité a été trouvée indépendante du champ électrique et de la densité de charges pour tous les OTFT étudiés. Enfin l’analyse des profils de potentiel dans le canal a mis en lumière des effets inattendus comme une diminution de la mobilité proche des contacts ou une évolution de la tension de seuil. / In this work, a surface potential measurement technique based on the Kelvin Force Probe Microscopy (KPFM), has been developed and applied to operating electronic devices. Potential profiles in the channel of organic transistors operated under high voltage (>10V) have been measured under ambient conditions. This original technique was used together with conventional current-voltage characterization and numerical simulation to gain a better understanding of carrier injection and transport properties in organic thin film transistors (TFTs). Various TFT structures and materials were studied (PTAA, DNTT, P3HT). The source intrinsic current-voltage characteristic was found either linear or non-linear depending on the device technology. Contact resistance measurements are 10 times more accurate than using the conventional « transmission line method» (TLM), and allow individual TFT characterization. Contact modeling was carried out using a quasi-2D numerical model, including an injection model from Arkhipov, and compared to measurements. New mobility and threshold voltage measurement methods, extracted from the KPFM potential profiles, are introduced. The KPFM measured channel mobility does not suffer from any contact influence. Surprisingly, the channel mobility was also found independent from the carrier concentration and from the electric field, on all the measured devices. Finally, unexpected effects could be evidenced from the potential profiles on some TFT structures: a reduction of the channel mobility occurs close to the contacts in some planar structures, and a shift of the threshold voltage was observed in staggered devices.
8

Time-Resolved Kelvin Probe Force Microscopy of Nanostructured Devices

Murawski, Jan 07 July 2016 (has links)
Since its inception a quarter of a century ago, Kelvin probe force microscopy (KPFM) has enabled studying contact potential differences (CPDs) on the nanometre scale. However, current KPFM investigations are limited by the bandwidth of its constituent electronic loops to the millisecond regime. To overcome this limitation, pump-probe-driven Kelvin probe force microscopy (pp-KPFM) is introduced that exploits the non-linear electric interaction between tip and sample. The time resolution surpasses the electronic bandwidth and is limited by the length of the probe pulse. In this work, probe pulse lengths as small as 4.5 ns have been realized. These probe pulses can be synchronized to any kind of pump pulses. The first system investigated with pp-KPFM is an electrically-driven organic field-effect transistor (OFET). Here, charge carrier propagation in the OFET channel upon switching the drain-source voltage is directly observed and compared to simulations based on a transmission line model. Varying the charge carrier density reveals the impeding influence of Schottky barriers on the maximum switching frequency. The second system is an optically-modulated silicon homojunction. Here, the speed of surface photovoltage (SPV) build-up is accessed and compared to timeaveraged results. Due to slow trap states, the time-averaged method is found to lack comprehensiveness. In contrast, pp-KPFM exposes two intensity-dependent recombination times on the same timescale — high-level Shockley-Read-Hall recombination in the bulk and heat-dominated recombination in the surface layer — and a delay of the SPV decay with rising frequency, which is attributed to charge carrier retention at nanocrystals. The third system is a DCV5T-Me:C60 bulk heterojunction. The SPV dynamics is probed and compared to measurements via open-circuit corrected transient charge carrier extraction by linearly increasing voltage. Both methods reveal an exponential onset of the band bending reduction that is attributed to the charge carrier diffusion time in DCV5T-Me, and a double exponential decay, hinting at different recombination paths in the studied organic solar cell. The above-mentioned experiments demonstrate that pp-KPFM surpasses conventional KPFM when it comes to extracting dynamic device parameters such as charge carrier retention and recombination times, and prove that pp-KPFM is a versatile and reliable tool for studying electrodynamics on nanosurfaces.
9

Quantitative dopant profiling in semiconductors: A new approach to Kelvin probe force microscopy

Baumgart, Christine 08 May 2013 (has links) (PDF)
Failure analysis and optimization of semiconducting devices request knowledge of their electrical properties. To meet the demands of today’s semiconductor industry, an electrical nanometrology technique is required which provides quantitative information about the doping profile and which enables scans with a lateral resolution in the sub-10 nm range. In the presented work it is shown that Kelvin probe force microscopy (KPFM) is a very promising electrical nanometrology technique to face this challenge. The technical and physical aspects of KPFM measurements on semiconductors required for the correct interpretation of the detected KPFM bias are discussed. A new KPFM model is developed which enables the quantitative correlation between the probed KPFM bias and the dopant concentration in the investigated semiconducting sample. Quantitative dopant profiling by means of the new KPFM model is demonstrated by the example of differently structured, n- and p-type doped silicon. Additionally, the transport of charge carriers during KPFM measurements, in particular in the presence of intrinsic electric fields due to vertical and horizontal pn junctions as well as due to surface space charge regions, is discussed. Detailed investigations show that transport of charge carriers in the semiconducting sample is a crucial aspect and has to be taken into account when aiming for a quantitative evaluation of the probed KPFM bias.
10

Modélisation des cellules solaires pérovskites, des dispositifs optoélectroniques III-V et de la microscopie à sonde de Kelvin / Modélisation des cellules solaires pérovskites, des dispositifs optoélectroniques III-V et de la microscopie à sonde de Kelvin

Huang, Yong 14 March 2018 (has links)
Ce travail de thèse se concentre sur l'étude des modèles de type drift-diffusion. Des approches sont développées pour la modélisation de la Microscopie à sonde de Kelvin, des cellules solaires à base de matériaux pérovskites (PSCs), des cellules solaires tandem de type pérovskite/silicium et des îlots quantiques lll-V/GaP. Tout d'abord, l'approche de la modélisation de la sonde de Kelvin est examinée pour la surface de TiOx et l'absorbeur pérovskite MAPbI3 Ensuite, des mesures avec sonde de Kelvin et des simulations sont proposées pour des jonctions diffuses à base de silicium et pour des PSCs à base de TiOx mésa poreux. Les variations du potentiel interne sont étudiées ouvrant la voie à une amélioration supplémentaire des dispositifs. L'influence de l'état de surface des couches wo. sur des mesures à sonde de Kelvin est étudiée théoriquement. Différents facteurs à l'origine des pertes de tension de circuit ouvert (Voc) des PSCs sont discutés. L'effet anormal d'hystérésis dans les PSCs est également simulé, en tenant compte des étals de pièges d'interface et des ions mobiles. En outre, le design de cellules solaires tandem 2T pérovskite/silicium est étudié en détails. Une jonction tunnel à base de silicium entre les deux sous-cellules supérieure et inférieure est proposée pour assurer le bon fonctionnement des cellules en série. L'influence du profil de dopage dans la jonction tunnel est discutée. Au final, le transport des porteurs dans les îlots quantiques III-V/GaP est étudié dans le cadre plus général de l'intégration d'émetteurs lll-V sur silicium. Les caractéristiques électroluminescentes et électriques de ces structures sont simulées dans une approximation cylindrique. / This PhD work focuses on optoelectronic device simulations based on drift-diffusion models. Approaches are developed for the modelling of Kelvin Probe Force Microscopy (KPFM), perovskite-based solar cells (PSCs), perovskite/silicon tandem solar cells and lll-V/GaP quantum dots (ODs). Firstly, a new approach for the modelling of KPFM is applied to TiOx slabs and to the MAPbI3 perovskite absorber. Secondly, KPFM measurements and simulations are proposed for silicon-based diffused junctions and mesoporous TiOx based PSCs. The built-in potential is investigated, and this study paves the way toward fu rther device improvements. In addition, the influence of the surface of WO. slabs on KPFM measurements is studied theoretically. Various facto rs influencing open circuit voltage (Voe) losses in PSCs are discussed. The abnormal hysteresis effect in the PSCs is simulated as well, considering interface trap states and mobile ions. The design of two-terminal perovskite/silicon tandem solar cells is studied in detail. A siliconbased tunnel junction between the top and the bottom subcells is proposed for serial current matching. The influence of the doping profile in the tunnel junction is discussed. At the end of the manuscript, the carrier transport in III-V/GaP QDs is investigated, for the integration of III-V emitters on silicon. The electroluminescence and electrical characteristics of these III -V light emitting devices are simulated by using a cylindrical approximation.

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