Dissertations / Theses on the topic 'Surface passivation'
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Osorio, Ruy Sebastian Bonilla. "Surface passivation for silicon solar cells." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:46ebd390-8c47-4e4b-8c26-e843e8c12cc4.
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Passivation of silicon surfaces remains a critical factor in achieving high conversion efficiency in solar cells, particularly in future generations of rear contact cells -the best performing cell geometry to date. In this thesis, passivation is characterised as either intrinsic or extrinsic, depending on the origin of the chemical and field effect passivation components in dielectric layers. Extrinsic passivation, obtained after film deposition or growth, has been shown to improve significantly the passivation quality of dielectric films. Record passivation has been achieved leading to surface recombination velocities below 1.5 cm/s for 1 Ωcm n-type silicon covered with thermal oxide, and 0.15 cm/s in the same material covered with a thermal SiO2/PECVD SiNx double layer. Extrinsic field effect passivation, achieved by means of corona charge and/or ionic species, has been shown to decrease by 3 to 10 times the amount of carrier recombination at a silicon surface. A new parametrisation of interface charge, and electron and hole recombination velocities in a Shockley-Read-Hall extended formalism has been used to model accurately silicon surface recombination without the need to incorporate a term relating to space-charge or surface damage recombination. Such a term is unrealistic in the case of an oxide/silicon interface. A new method to produce extrinsic field effect passivation has been developed in which charge is introduced into dielectric films at high temperature and then permanently quenched in place by cooling to room temperature. This approach was investigated using charge due to one or more of the following species: ions produced by corona discharge, Na+, K+, Cs+, Mg2+ and Ca2+. It was implemented on both single SiO2 and double SiO2/SiNx dielectric layers which were then measured for periods of up to two years. The decay of the passivation was very slow and time constants of the order of 10,000 days were inferred for two systems: 1) corona-charge-embedded into oxide grown on textured FZ-Si, and 2) potassium ions driven into an oxide on planar FZ-Si. The extrinsic field effect passivation methods developed in this work allow more flexibility in the combined optimisation of the optical properties and the chemical passivation properties of dielectric films on semiconductors. Increases in cell Voc, Jsc and η parameters have been observed in simulations and obtained experimentally when extrinsic field effect passivation is applied to the front surface of silicon solar cells. The extrinsic passivation reported here thus represents a major advancement in controlled and stable passivation of silicon surfaces, and shows great potential as a scalable and cost effective passivation technology for solar cells.
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Chang, Wai-Kit. "Porous silicon surface passivation and optical properties." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41426.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996."June 1996."
Includes bibliographical references (leaves 84-85).
by Wai-Kit Chang.
S.M.
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Sun, Shiyu. "Germanium surface cleaning, passivation, and initial oxidation /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Michalak, David Jason Gray Harry B. "Physics and chemistry of silicon surface passivation /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-05082006-074414.
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Antu, Antara Debnath. "Morphology and Surface Passivation of Colloidal PbS Nanoribbons." Bowling Green State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1499383746861722.
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Benrabah, Sabria. "Passivation des matériaux III-N de type GaN." Thesis, Lyon, 2021. http://www.theses.fr/2021LYSE1310.
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Pour répondre aux demandes de développement de nouveaux produits dans les domaines des convertisseurs électroniques de puissance pour les voitures électriques, des panneaux solaires, des éoliennes et des nouvelles technologies d'éclairage à base de LED ou de composants RF, la recherche s'est concentrée sur les matériaux à large bande interdite directe, dont le nitrure de gallium (GaN). Le GaN a suscité un grand intérêt en raison de ses propriétés exceptionnelles pour les dispositifs électroniques de puissance de la prochaine génération. Avec une vitesse de saturation élevée et une tension de fonctionnement élevée, les dispositifs à base de GaN peuvent fonctionner à haute fréquence et avec un excellent rendement, ce qui fait du GaN un matériau de choix dans les applications de puissance. Cependant, le développement des matériaux III-N est encore immature, notamment en ce qui concerne le contrôle de la qualité des différentes interfaces au sein des dispositifs. La présence d'une forte densité d'états d'interfaces peut être à l'origine de dysfonctionnements du dispositif. Par conséquent, la compréhension et le contrôle de la surface du GaN constituent un défi pour une éventuelle intégration industrielle future. Aujourd'hui, il n'existe pas de préparation de surface standard appropriée et efficace pour le GaN. Afin d'étudier ce problème, ce projet de thèse a été réalisé dans le cadre d'une collaboration entre le CEA-LETI (Grenoble), le LTM (Grenoble) et les laboratoires CP2M (Catalyse, Polymérisation, Procédés et Matériaux, Lyon). Les principaux objectifs de ce projet sont, d'une part, de comprendre la chimie de surface suite à différentes préparations de surface, et d'autre part, de mettre en place la configuration des liaisons de surface. Ce projet de thèse s'est donc concentré sur la préparation et la caractérisation de l'extrême surface de GaN après divers traitements chimiques et physiquesTo meet demands for the development of new products in the fields of power electronic convertors for electric cars, solar panels, wind turbines, and new LED-based lightening technologies or RF components, research has focused on direct wide bandgap materials, including Gallium Nitride (GaN). GaN has attracted significant interest due to its exceptional properties for next-generation power electronic devices. With a high saturation velocity and a high operating voltage, GaN-based devices can operate at high frequency and with excellent efficiency, making GaN a material of choice in power applications. However, the development of III-N materials is still immature, especially in terms of quality control of the various interfaces within the devices. The presence of high density of interfaces states can be the cause of device malfunctions. Therefore, understanding and controlling the surface of GaN is a challenge for possible future industrial integration. Today, there is no suitable and effective standard surface preparation of GaN. In order to investigate this problem, this PhD project was carried out in a collaboration between CEA-LETI (Grenoble), LTM (Grenoble) and CP2M laboratories (Catalysis, Polymerisation, Process and Materials, Lyon). The main objectives of this project are, first, to understand the surface chemistry following various surface preparations, and second, to set up the configuration of surface bonds. Therefore, this PhD project focused on the preparation and characterisation of the extreme surface of GaN after various chemical and physical treatments
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Flynn, Christopher Richard ARC Centre of Excellence in Advanced Silicon Photovoltaics & Photonics Faculty of Engineering UNSW. "Sputtering for silicon photovoltaics: from nanocrystals to surface passivation." Awarded by:University of New South Wales. ARC Centre of Excellence in Advanced Silicon Photovoltaics & Photonics, 2009. http://handle.unsw.edu.au/1959.4/44686.
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Deposition of thin material films by sputtering is an increasingly common process in the field of silicon (Si)-based photovoltaics. One of the recently developed sputter-deposited materials applicable to Si photovoltaics comprises Si nanocrystals (NCs) embedded in a Si-based dielectric. The particular case of Si nanocrystals in a Silicon Dioxide (SiO2) matrix was studied by fabricating metal-insulator-semiconductor (MIS) devices, in which the insulating layer consists of a single layer of Si NCs in SiO2 deposited by sputtering (Si:NC-MIS devices). These test structures were subjected to impedance measurements. The presence of Si NCs was found to result in two distinct capacitance peaks. The first of these peaks is attributable to the small signal response of states at the insulator/substrate interface, enhanced by the presence of fixed charge associated with the NC layer. The second peak, which occurs without precedent, is due to external inversion layer coupling, in conjunction with a transition between tunnel-limited and semiconductor-limited electron current. Si:NC-MIS devices are also potential test structures for energy-selective contacts, based on SiO2/Si NC/SiO2 double barrier structures fabricated by sputtering. Using a one-dimensional model, current-voltage (I-V) curve simulations were performed for similar structures, in which the Si NCs are replaced by a Si quantum well (QW). The simulations showed that for non-degenerately doped Si substrates, the density of defects in the SiO2 layers can strongly influence the position of I-V curve structure induced by QW quasi-bound states. Passivation of crystalline Si (c-Si) surfaces by sputter-deposited dielectric films is another major application of sputtering for Si photovoltaics. This application was explored for the cases of sputtered SiO2 and hydrogenated Silicon Oxy-Carbide (SiOC:H). For the case of sputtered SiO2, an effective surface recombination velocity of 146 cm/s was achieved for an injection level of 1E15 cm???3. The investigated SiOC:H films were found to be unsuitable for surface passivation of Si, however their passivation performance could be slightly improved by first coating the Si surface with a chemically-grown or sputtered SiO2 layer. The investigations performed into specific aspects of sputter-deposited SiO2, Si NCs, and SiOC:H have highlighted important properties of these films, and confirmed the effectiveness of sputtering as a deposition technology for Si photovoltaics.
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Pereau, Alban Jean-Joel. "Rear surface passivation for high efficiency silicon solar cells." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2828.
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In order to adapt laser grooved buried contact (LGBC) solar cells to a thinner silicon substrate than usually used, we have investigated the reduction of charge carrier loss at the rear surface of p-type silicon wafers by plasma-enhanced chemical vapour deposition (PECVD) of a-Si:H and SiNx films. The efficiency of these passivating films has been measured via the surface recombination velocity (SRV) which is wanted as low as possible. The SRV values of our samples have been compared with the expected theoretical values given by the Shockley-Read Hall (SRH) recombination model. SRH theory is a description of the electron-hole recombination via defects inducing energy levels in the forbidden bandgap. This way of recombination is the predominant mode for semiconductors with indirect bandgaps like silicon. Two influential factors in regard to SRV can be understood from this theory. These two factors are the electron to hole capture cross section ratio and the fixed charge density Qf at the silicon substrate/film interface. These two factors induce an asymmetry between the electron and the hole recombination and are responsible for the excess charge carrier concentration dependence of the SRV. In other words, the SRV depends on the illumination intensity. In this work, the SRV has been measured for an excess charge carrier injection level in the 1.1013-1.1016 cm-3 range and then it has been compared with the theoretical value given by the SRH theory in order to determine the fixed charge density and have an estimation of the defect characteristics including its density. Simulations of LGBC cells under one sun illumination have then been performed using the PC1D5 software. The measured SRV value corresponding to one sun has been integrated in the simulation and the expected efficiency has been extracted as a function of the wafer thickness. It results from this study that 150μm LGBC solar cells can theoretically have an efficiency of 19% by the integration of passivating SiNx films. A second aspect of this work is an effort to understand the relation between the passivating film quality, structure, and the PECVD parameters during deposition. The films have been characterized principally by ellipsometry and also by XPS. All of our SiNx films are located in the Si-rich region (x<1.1) and the passivating quality increases with x.
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Motahari, Sara. "Surface Passivation of CIGS Solar Cells by Atomic Layer Deposition." Thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127430.
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Thin film solar cells, such as Cu(In,Ga)Se2, have a large potential for cost reductions, due to their reduced material consumption. However, the lack in commercial success of thin film solar cells can be explained by lower efficiency compared to wafer-based solar cells. In this work, we have investigated the aluminum oxide as a passivation layer to reduce recombination losses in Cu(In,Ga)Se2 solar cells to increase their efficiency. Aluminum oxides have been deposited using spatial atomic layer deposition. Blistering caused by post-deposition annealing of thick enough alumina layer was suggested to make randomly arranged point contacts to provide an electrical conduction path through the device. Techniques such as current-voltage measurement, photoluminescence and external quantum efficiency were performed to measure the effectiveness of aluminum oxide as a passivation layer. Very high photoluminescence intensity was obtained for alumina layer between Cu(In,Ga)Se2/CdS hetero-junction after a heat treatment, which shows a reduction of defects at the absorber/buffer layers of the device.
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St-Arnaud, Ken. "Traitements de passivation des surfaces de l'arséniure de gallium et impact sur les propriétés électro-optiques de ce matériau." Mémoire, Université de Sherbrooke, 2015. http://hdl.handle.net/11143/7723.
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Ce projet de recherche vise à caractériser l'influence de divers traitements de passivation de surface de l'arséniure de gallium (GaAs) sur les propriétés électriques et optiques de ce matériau. Les procédés de passivation étudiés sont les traitements au soufre (NH[indice inférieur 4])[indice inférieur 2]S et les dépôts de nitrure de silicium SiN[indice inférieur x] et trois types de substrat ont été utilisés à titre comparatif, un type N (10[indice supérieur 16]), un type N+ (10[indice supérieur 18]) et un non dopé. Dans ce dernier cas, un système de déposition chimique en phase vapeur assistée par plasma (PECVD) a été utilisé et l'influence de la fréquence de la source d'alimentation AC du plasma a été étudiée. Des techniques de caractérisation électrique, optique et électro-optique ont été utilisées pour l'étude. Des structures métal-isolant-semiconducteur (MIS) ont été réalisées pour les mesures AC et DC de capacité à plusieurs fréquences. L'analyse des mesures électriques a permis de démontrer un plus grand détachement du niveau de Fermi pour les échantillons passivés avec un dépôt de nitrure de silicium SiN[indice inférieur x] à basse fréquence plutôt qu'à haute fréquence. Des mesures optiques en continu et résolue en temps ont été effectuées sur une série d'échantillons de GaAs présentant différents niveaux de dopage et différents traitements de surface. Les mesures de photoluminescence en continu et les mesures résolues en temps montrent que les propriétés optiques des dispositifs dépendent grandement du type de substrat utilisé. Plus d'information sur le champ surfacique des dispositifs est nécessaire pour conclure sur l'efficacité de la passivation. Pour obtenir cette information, des mesures de photoluminescence, continues et résolues en temps, ont aussi été effectuées sur les structures MIS en présence d'un champ électrique. Ces mesures n'ont pas permis de mettre en évidence l'influence de la modification du champ de surface sur l'intensité du signal de luminescence, et ce peu importe le procédé de traitement de surface utilisé. Finalement, des antennes THz ont été fabriquées sur un substrat de SI-GaAs passivé par le traitement PECVD à basse fréquence. Ces antennes émettent un champ THz plus intense et avec un plus grand contenu fréquentiel que celle fabriquée sans traitement de passivation.
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Dahal, Arjun. "Surface Science Studies of Graphene Interfaces." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5820.
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Interfaces between graphene and dissimilar materials are needed for making devices, but those interfaces also modify the graphene properties due to charge transfer and/or symmetry breaking. In this dissertation we investigate the technology of preparing graphene on different substrates and how the substrate influences the electronic properties of graphene.
Synthesizing large area graphene on late transition metals by chemical vapor deposition is a promising approach for many applications of graphene. Among the transition metals, nickel has advantages because the good lattice match and strong interaction between graphene/Ni(111) enables the synthesis of a single domain of graphene on Ni(111). However, the nickel substrate alters the electronic structure of graphene due to substrate induced symmetry breaking and chemical interaction of the metal d-band with graphene. Similar chemical interactions are observed for other transition metals with a d-band close to the Fermi-level. On the other hand, graphene mainly physisorbs on transition metals with a lower lying d-band center. In this thesis we investigate the growth of graphene on nickel by vacuum chemical vapor deposition (CVD). In particular, we present our studies of graphene synthesis on Ni(111) substrates. We demonstrate the self-limiting monolayer of single domain of graphene can be grown on single crystal Ni(111). Our studies also show that selective twisted bilayer graphene can be grown by carbon segregation on Ni(111)-films. To modify the interaction between graphene and the nickel substrate we investigated the intercalation of tin. In the case of graphene physisorbed on weakly interacting metals, some charge doping of graphene occurs due to work function differences between graphene and the metal. Using x-ray photoemission spectroscopy (XPS) we correlate the charge doping of graphene on different metals with the C-1s binding energy. This study demonstrate that XPS can be used to determine the Fermi-level in graphene. While metal intercalation can alter the interaction with the substrate it does not avoid overlap of electronics states at the Fermi-level. Therefore a band gap material should be inserted between the graphene and the metal growth substrate (in this case Pt(111)). This is accomplished by oxidation of intercalated iron at elevated oxygen pressure. We demonstrate that a 2D-FeO layer can be formed in between graphene and the Pt(111) surface. We discuss the role of the 2D-FeO moiré-structure on the nanoscale electronic properties of graphene.
To date good quality graphene can only be grown by CVD on late transition metals. To obtain graphene on other substrates the graphene can be transferred mechanically from a growth substrate to various other materials. We demonstrate that this transfer can also be achieved to tungsten, an early transition metal that easily forms a carbide. In our studies to avoid oxidation of the tungsten substrate and reaction of the graphene with the tungsten substrate under thermal treatment, protection of the W(110) surface with sulfur has been explored.
For the integration of graphene into device architectures, graphene has to be interfaced with high-κ dielectrics. However, because of the inert nature of graphene, most high-κ do not wet graphene and thus preventing formation of contiguous dielectric layers. Yttrium oxide (Y2O3) has been demonstrated to be an exception and we characterized the growth of Y2O3 on various metal supported graphene and graphene transferred to SiO2. We showed that such a Y2O3 layer can also act as seeding layer for the growth of alumina, which is the preferred dielectric material in many applications. Finally, we investigate the charge doping of graphene in a metal/graphene/dielectric stack and find that the charge doping of graphene is a function of both the work function of the metal as well as the covering dielectric. Thus the dielectric layer can modify the charge doping of graphene at a metal contact.
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Ek, Anton. "Silicon surface passivation via ultra-thin SiO2, TiO2, and Al2O3 layers." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75913.
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Energy traps at the silicon surface originating from discontinuities in the lattice is detrimental to the performance of solar cells. Acting as recombination centers, they offer a location where the charge carriers may easily return to their original energy band after excitation. Surface passivation is an effective method to combat this and can be done either by suppressing traps (lowering trap density) or by forming an electric field, preventing the carriers from reaching the defect states. Silicon oxide, SiO2, and aluminum oxide, Al2O3, are two materials which have previously been shown to provide good passivating qualities. In this thesis, SiO2 and Al2O3 have been used both as single layers and in a stack configuration to passivate the surface of crystalline silicon (c-Si). Using a response surface methodology approach, temperature optimization with respect to deposition and annealing temperature has been conducted for SiO2/Al2O3 stacks deposited with plasma-enhanced atomic layer deposition, PEALD. It was shown that the same deposition temperature (Tdeposition = 140 °C, Tanneal = 395 °C) could be used for both materials and provide good passivation with an effective surface recombination velocity, Seff, of 5.3 cm/s (1Ωcm n-type Si wafers). From FTIR measurements, an increase in hydroxyl groups was seen as the SiO2 deposition temperature increased while the opposite was observed for Al2O3 which also showed fewer carbon related impurities with increasing temperature. Increasing the SiO2 temperature strongly affected the fixed charge density, causing it to decrease and even switch polarity. The fixed charge density could also be controlled by varying the thickness of the intermediate SiO2 layer. At a thickness of 1-2 nm, a minimum in the effective lifetime was observed and was correlated to Si close to flat-band conditions. N-type wafers showed a larger negative fixed charge density than p-type wafers which results in stronger field-effect passivation. For phosphorous doped emitters (200 Ω/sq on 10 Ωcm p-type wafer), it was seen that SiO2/Al2O3 stacks with a SiNx anti-reflection coating performed better than SiO2 or Al2O3 single layers. By depositing SiO2 at 130 °C in SiO2/Al2O3 stacks and annealing at 450 °C, an implied open circuit voltage (iVoc) of 710 mV was measured (AM1.5G) together with an implied fill factor (iFF) of 84.1% and a recombination parameter (J0) of 19.2 fA/cm2. Al2O3 single layer showed an extremely low J0 of 10 fA/cm2 but suffered from a decreased iFF and strong injection dependent lifetimes which originates from an inversion layer. ALD ozone processes were successfully developed for SiO2 and Al2O3. The deposition rate per cycle for SiO2 was found to be only ~0.175 Ǻ/cycle (PEALD ~1.1 Ǻ/cycle), making it rather unpractical for use outside of research. Single layer SiO2 deposited with ozone showed, similarly to a plasma process, almost no surface passivation. Al2O3 however proved to be highly passivating on its own with a τeff = 3.8 ms, Seff = 1.2 cm/s (1 Ωcm n-type) after depositing at 250 °C. Studies on the effect of annealing showed that an annealing temperature of 450 °C is necessary to completely activate the passivation. The low Seff values were attributed to a very high negative fixed charge density ~1013 cm-2 together with strong chemical passivation.
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Qui, Jianhai. "A study by solution and surface analysis of passivation of stainless steel." Thesis, University of Surrey, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328789.
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Bastola, Ebin. "CdTe Back Contact Engineering via Nanomaterials, Chemical Etching, Doping, and Surface Passivation." University of Toledo / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596813646708798.
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Sorrenti, Estelle. "Étude de la passivation de la pyrite : chimie de surface et réactivité." Thesis, Vandoeuvre-les-Nancy, INPL, 2007. http://www.theses.fr/2007INPL054N/document.
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Afin de lutter contre les phénomènes de drainage minier acide DMA, nous avons étudié la possibilité de passivation/inertage de rejets miniers sulfurés. L'inhibition de l'oxydation superficielle de phases pyriteuses a été effectuée par adsorption de molécules: acide humique HA, thymol et silicate de sodium. L'étude fondamentale réalisée sur une pyrite pure (masse 1-5g) a ensuite été conduite à des rejets miniers (masse 2 kg). L’adsorption de molécules passivantes a été réalisée dans des conditions dynamiques (colonne chromatographique) et statiques (batch). L’ordre d’efficacité est: acide humique> thymol>silicate de sodium. Les essais dynamiques ont montré que l’adsorption d'HA sur la pyrite est irréversible. L’étude par voltamétrie cyclique a montré que de faibles concentrations en HA adsorbée (de 0,15 à 0,3mg/g–[thêta]<1) sont suffisantes pour bloquer plus de 90% de l’activité électrochimique initiale. L’analyse de la surface par la spectroscopie IR en mode réflexion diffuse a mis en évidence l’importance des phases oxydées superficielles dans le processus d’adsorption. La description des fronts chromatographiques a été possible à partir du modèle trimodal dynamique basé sur l’existence de trois sites d’adsorption dont la nature chimique, le nombre et l’accessibilité évoluent pendant l’adsorption. D'autres expériences conduites en cellules humides simulant le comportement d’un stérile minier d'Abitibi-Témiscamingue en conditions naturels de stockage, ont montré que le traitement à l’HA est efficace pendant plus de 30 équivalent-années. Aussi, un stérile traité avec HA ne génère plus de DMA alors que celui non traité est générateur d’acide pendant les 6 premières annéesTo fight against the phenomena of acid mine drainage DMA, we studied the possibility of passivation/inertage of sulphurized mining discharges. The inhibition of the superficial oxidation of pyriteuses phases was made by adsorption of molecules: acid humique HA, thymol and silicate of sodium. The fundamental study realized on a pure pyrite (mass 1-5g) was then driven to mining refusals (masse 2 kg). The adsorption of passivantes molecules was realized in dynamic conditions (chromatographic column) and statics (batch) . The order of efficiency is: acid humique > thymol > silicate of sodium. The dynamic experiments showed that the adsorption of HA on the pyrite is irreversible. The study by cyclic voltammetry showed that weak concentrations in adsorbed HA (of 0,15 in 0,3mg/g–[thêta]<1) are sufficient to block more than 90 % of the initial electrochemical activity. The analysis of the surface by the spectroscopy IR in mode diffuse reflection put in evidence the importance of the superficial oxidized phases in the process of adsorption. The description of chromatographic fronts was possible from the model dynamic trimodal based on the existence of three sites of adsorption among which the chemical nature, the number and the accessibility evolve during the adsorption. Other experiments led in wet cells feigning the behavior of sterile one mining of natural Abitibi-Témiscamingue in conditions of storage, showed that the treatment in the HA is effective counterpart more than 30 equivalents-years. So, sterile one treated with HA generate no more DMA while that untreated is generative of acid during the first 6 years
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Hofmann, Marc. "Rear surface conditioning and passivation for locally contacted crystalline silicon solar cells." München Verl. Dr. Hut, 2008. http://d-nb.info/992163250/04.
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Sorrenti, Estelle De Donato Philippe Gorner Tatiana. "Étude de la passivation de la pyrite chimie de surface et réactivité /." S. l. : INPL, 2007. http://www.scd.inpl-nancy.fr/theses/2007_SORRENTI_E.pdf.
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Brody, Jed. "Doping dependence of surface and bulk passivation of multicrystalline silicon solar cells." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180041/unrestricted/brody%5Fjed%5F200312%5Fphd.pdf.
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Lebreton, Fabien. "Silicon surface passivation properties of aluminum oxide grown by atomic layer deposition for low temperature solar cells processes." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX109/document.
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Cette thèse se focalise sur les propriétés passivantes octroyées par des couches minces d’Al2O3 déposées par Atomic Layer Deposition (ALD) à partir de TMA et H2O pour les cellules photovoltaïques en silicium ayant des températures de fabrication inférieures à 400 °C. La première partie de ce travail de doctorat vise à identifier les mécanismes de formation des charges électrostatiques négatives présentes dans l’oxyde d’aluminium. Pour ce faire, les effets de l’illumination post-dépôt (à savoir le flux et l’énergie des photons), ainsi que la température du substrat ont été étudiés. Il a été constaté qu’au moins 70 % de ce qu’on appelle généralement les « charges fixes » sont en fait des charges piégées résultant de l’injection d’électrons du substrat de silicium dans l’oxyde d’aluminium. Par la suite, nous avons étudié l’influence des paramètres de dépôt de l’Al2O3 ainsi que l’impact des traitements post-dépôt sur le piégeage des charges et donc sur les performances passivantes qui en résulte au sein d’un empilement Al2O3/a-SiNX:H déposé sur du silicium cristallin de type p. Les liens entre l’épaisseur de l’Al2O3, la qualité et la durabilité de la passivation ont pu être établis. Le meilleur compromis s’est avéré être aux alentours 60 cycles ALD (~ 6 nm), permettant une durée de vie des porteurs de charges minoritaires allant jusqu’à 4500 μs. La deuxième partie de ce travail doctoral porte sur les mécanismes de dégradation de la passivation. La formation de cloques à l’interface c-Si/Al2O3 est le premier mécanisme de dégradation étudié. Grâce à la microscopie acoustique colorée, la dégradation de l’interface Al2O3/c-Si lors de l’épaississement de l’Al2O3 a été confirmée, mais également lors la réduction de sa température de dépôt, c’est-à-dire en augmentant sa teneur en hydrogène. Une dérive thermique pendant l’ALD (TD-ALD) a été utilisée pour résoudre ce problème de cloquage. L’augmentation continue de la température du substrat pendant le dépôt favorise la libération de l’hydrogène à partir de l’interface c-Si/Al2O3. Pour 60 cycles ALD, le TD-ALD a permis d’augmenter la durée de vie des porteurs de charges jusqu’à 5500 μs. Enfin, l’affaiblissement de la passivation par effet de champ résultant des charges positives dans la couche de protection a-SiNX:H a été mis en évidence par simulation numérique. Les propriétés du a-SiNX:H ont été expérimentalement optimisée grâce à une approche par plan d’expérience. Une nouvelle couche mince d’a-SiNX: H contenant 50 % de charges fixes positives en moins a permis d’obtenir une durée de vie des porteurs de charges de 8800 μs pour 60 cycles de TD-ALD, c’est-à-dire une vitesse de recombinaison de surface exceptionnelle basse de 0,8 cm.s-1This thesis focuses on the passivation properties provided by thin Al2O3 films grown by atomic layer deposition (ALD) from TMA and H2O for silicon solar cells having process temperatures lower than 400 °C. The first part of this doctoral work aims at identifying the formation mechanisms of negative electrostatic charges in aluminium oxide. Thus, the effects of post-deposition illumination (namely photon flux and photon energy), as well as substrate temperature were investigated. It was found that at least 70 % of what are generally named “fixed charges” are in fact trapped charges resulting from the injection of carriers from the silicon substrate into the aluminium oxide. From this result, we studied the influence of Al2O3 deposition parameters and post-deposition treatments on charge trapping and resulting passivation performances within an Al2O3/a-SiNX:H stack on p-type c-Si. The dependence of passivation performance (and stability) on Al2O3 thickness has been highlighted. Best compromise has been found to be around 60 ALD cycles (~6 nm), providing a lifetime up to 4500 µs. The second part of this PhD deals with the degradation mechanisms of passivation. Blistering at the c-Si/Al2O3 interface is the first studied degradation mechanism. Thanks to coloured picosecond acoustic microscopy, the Al2O3/c-Si adhesion has been confirmed to be reduced by Al2O3 thickening but also by the reduction of its deposition temperature, i.e. an increase of hydrogen content. A thermal drift during ALD (TD-ALD) has been used to solve this blistering issue. Gradual increase of the substrate temperature during the growth favours the release of hydrogen from the wafer/Al2O3 interface. For 60 ALD cycles, TD-ALD increased the lifetime up 5500 µs. Finally, the weakening of the electrostatic passivation arising from the positive charges in a-SiNX:H capping layer has been underlined by finite element simulations. The a-SiNX:H properties have been experimentally tuned thanks to a design of experiment approach. New a-SiNX:H capping containing 50 % less positive fixed charges resulted in a lifetime of 8800 µs for 60 TD-ALD cycles, i.e. an outstanding surface recombination velocity of 0.8 cm.s-1
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Ferré, Tomàs Rafel. "Surface passivation of crystalline silicon by amorphous silicon carbide films for photovoltaic applications." Doctoral thesis, Universitat Politècnica de Catalunya, 2008. http://hdl.handle.net/10803/6350.
Full textAbstract:
En aquesta tesi s'estudia la passivació del silici cristal·lí per a la producció de cèl·lules solars d'alta eficiència (> 20%) a baix preu.Actualment la indústria fotovoltaica empra capes de nitrur de silici crescut mitjançant la tècnica PECVD. Com a alternativa, es presenta el carbur de silici amorf (a-SiC), també crescut mitjançant PECVD. Resultats anteriors mostren que la passivacio del silici a partir de carbur de silici amorf son excel·lents quan el material és ric en silici i dopat amb fòsfor. L'alt contingut en silici provoca absorció de la llum a la capa, que no es tradueix en corrent elèctric, fent d'aquesta manera que el material sigui només útil quan s'aplica a la cara no il·luminada de la cèl·lula.
L'objectiu d'aquesta tesi és millorar les propietats de passivació del carbur de silici afegint els requisits indispensables en cèl·lules solars: uniformitat, transparència i propietats antireflectants, estabilitat a llarg termini i enfront altes temperatures. A part de les aplicacions tecnològiques també es pretèn entendre millor les propietats fonamentals de passivació.
Els principals resultats són:
- La passivació millora a mesura que s'incrementa el gruix de la capa de a-SiC, fins arribar a una saturació a partir de 50 nm. El mecanisme responsable es una millor saturació dels defectes de la interficie amb hidrogen. Al contrari del que es pensava a priori, la càrrega el·lèctrica emmagatzemada a la capa es manté constant amb el gruix.
- Experiments amb "corona charge" indiquen que l'origen de la càrrega el·lèctrica que produeix la passivació per efecte de camp es troba en la densitat d'estats a la interfície.
- No ha estat possible trobar una capa tranparent (rica en carboni) amb bona passivació. La millor aproximació per combinar passivació més transparència és emprar dues capes, una molt prima rica en silici per passivar i l'altra rica en carboni per aconseguir les propietats antireflectants adequades. S'ha optimitzat el gruix de la capa rica en silici per aconseguir un compromís entre la pèrdua de corrent degut a l'absorció de la llum a la capa i les propietats de passivació. Aquesta combinació de doble capa s'ha fet servir per passivar bases tipus p i emissors tipus n amb resultats excel·lents. Finalment, amb la doble capa es va poder fabricar la primera cèl·lula passivada amb carbur de silici amb una eficiencia > 20%.
- S'ha desenvolupat un material nou: l'al·leació de silici, carboni i nitrogen dopada amb fòsfor. Aquest material ha donat els millors resultats de passició fins ara obtingut dins el nostre grup en bases tipus p i tipus n i en emissors tipus n. La composició òptima és rica en silici i la combinació de capes dobles amb diferents composicions, com en el cas anterior, torna a donar bons resultats de passivació i transparència.
- S'han desenvolupat experiments d'estrès tèrmic a alta temperatura. Les propietats de passivació es veuen fortament afectades desprès de l'estrès si les capes són riques en silici. D'altra banda, les dobles capes mostren una estabilitat molt més alta a l'estrès tèrmic.
The thesis focuses on the study of surface passivation of crystalline silicon to produce high efficiency solar cells (with conversion efficiencies > 20%) at reduced prices. The state of the art in surface passivation is done by thin films of amorphous silicon nitride grown by Plasma Enhanced Chemical Vapour Deposition (PECVD) and it is a very well established material in the photovoltaic field.
In this thesis we offer an alternative that is based on amorphous silicon carbide (a-SiC), also grown by PECVD. The passivation properties of silicon carbide have been already studied in our group finding that excellent results can be obtained when the films are rich in silicon, especially for those doped with phosphorus to make a n-type material. Because this feature leads to undesirable absorption of solar light within the films that does not contribute to the photocurrent, silicon carbide would then be relegated to passivate only the rear side of the solar cell.
The aim of this work is to improve surface passivation properties developed previously and add compulsory requisites for the application of crystalline solar cells. These requisites are: uniformity, transparency and antireflective properties, stability under long term operation and stability under high temperature steps (allowing screen printing processes). Also it is the willing to provide a better understanding of the fundamental properties.
The main results achieved are enumerated hereafter:
- Surface passivation improves with the film thickness and then saturates for films thicker than 50 nm. The mechanism responsible for this improvement is not an increase of the electric charge in the film, as in principle could be thought, but a better saturation of defects by the presence of hydrogen. The amount of charge density seems to be independent of the film.
- Experiments of corona charge reveal some treats about the nature of the charge density to provide the field effect passivation. The origin of the charge seems to be a continuous density of states at the interface, rather a fixed charge allocated in the film.
- None of the attempts using carbon rich films, which are transparent and with antireflective properties, resulted in excellent surface passivation. Such attempts included variation of the deposition parameters, use of remote plasma PECVD with high incorporation of hydrogen, and introduction of nitrogen of in the phosphorus doped a-SiC films. Therefore, up to now it becomes apparent that it is a fundamental property of silicon carbide films the necessity to be rich in silicon to perform surface passivation.
- The way to combine surface passivation and antireflective properties was applying stacks of different a-SiC layers: one silicon rich and one carbon rich. The thickness of the silicon rich layer was optimized to reach a trade-off between level of passivation and lost of photocurrent due to the absorption in the film. The stacks were used to passivate p-type bases, with reasonably good results, and n+- type emitters, with very good results. The stacks provided the the first silicon solar a-SiC rear side passivated with efficiency above 20%.
- A new material was tested: a ternary alloy of silicon, carbon and nitrogen doped with phosphorus. This material was applied to n- and p-type bases and n+-type emitters, presenting the best results in surface passivation achieved by our group, and comparable to surface passivation record achieved by amorphous silicon carbide. Best composition was rich in silicon, and again stacks of silicon rich and carbon rich films was combined successfully.
- Stability against thermal processes was tested on different passivation schemes. After the treatment, the passivation is strongly reduced for single silicon rich films, which were offering good initial results. On the other hand, the stacks with a second carbon rich film maintain reasonably well the surface passivation properties.
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Ohno, Yutaka, Takeshi Nakao, Shigeru Kishimoto, Koichi Maezawa, and Takashi Mizutani. "Effects of surface passivation on breakdown of AlGaN/GaN high-electron-mobility transistors." American Institute of Physics, 2004. http://hdl.handle.net/2237/7005.
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Liu, Jian. "Passivation effects of surface iodine layer on tantalum for the electroless copper deposition." Thesis, University of North Texas, 2004. https://digital.library.unt.edu/ark:/67531/metadc5546/.
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The ability to passivate metallic surfaces under non-UHV conditions is not only of fundamental interests, but also of growing practical importance in catalysis and microelectronics. In this work, the passivation effect of a surface iodine layer on air-exposed Ta for the copper electroless deposition was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Although the passivation effect was seriously weakened by the prolonged air exposure, iodine passivates the Ta substrate under brief air exposure conditions so that enhanced copper wetting and adhesion are observed on I-passivated Ta relative to the untreated surface.
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Joel, Jonathan. "Characterization of Al2O3 as CIGS surface passivation layer in high-efficiency CIGS solar cells." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-230228.
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In this thesis, a novel method of reducing the rear surface recombination in copper indium gallium (di) selenide (CIGS) thin film solar cells, using atomic layer deposited (ALD) Al2O3, has been evaluated via qualitative opto-electrical characterization. The idea stems from the silicon (Si) industry, where rear surface passivation layers are used to boost the open-circuit voltage and, hence, the cell efficiency. To enable a qualitative assessment of the passivation effect, Al/Al2O3/CIGS metal-oxide-semiconductor (MOS) devices with 3-50 nm oxide thickness, some post-deposition treated (i.e. annealed), have been fabricated. Room temperature capacitance-voltage (CV) measurements on the MOS devices indicated a negative fixed charge density (Qf) within the Al2O3 layer, resulting in a reduced CIGS surface recombination due to field effect passivation. After annealing the Al2O3 passivation layers, the field effect passivation appeared to increase due to a more negative Qf. After annealing have also indications of a lower density of interface traps been seen, possibly due to a stronger or activated chemical passivation. Additionally, the feasibility of using ALD Al2O3 to passivate the surface of CIGS absorber layers has also been demonstrated by room temperature photoluminescence (PL) measurements, where the PL intensity was about 20 times stronger for a structure passivated with 25 nm Al2O3 compared to an unpassivated structure. The strong PL intensity for all passivated devices suggests that both the chemical and field effect passivation were active, also for the passivated as-deposited CIGS absorbers.
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Chakroun, Ahmed. "Passivation de la surface du nitrure de gallium par dépôt PECVD d'oxyde de silicium." Thèse, Université de Sherbrooke, 2015. http://hdl.handle.net/11143/6735.
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Le nitrure de gallium (GaN) est un matériau semi-conducteur de la famille III-V à large bande interdite directe, ayant des propriétés électriques et thermiques intéressantes. Grâce à sa large bande interdite, son fort champ de claquage et sa forte vitesse de saturation, il est très convoité pour la réalisation de dispositifs électroniques de puissance et de hautes fréquences pouvant fonctionner à haute température. De plus, grâce au caractère direct de sa bande interdite et son pouvoir d’émission à faible longueur d’onde, il est aussi avantageux pour la réalisation de dispositifs optoélectroniques de hautes performances en émission ou en détection tels que les DELs, les lasers ou les photo-détecteurs.
Les difficultés de son élaboration, les problèmes d’inefficacités du dopage p et les densités élevées de défauts cristallins dans les couches épitaxiées ont constitué pendant longtemps des handicaps majeurs au développement des technologies GaN. Il a fallu attendre le début des années 1990 pour voir apparaître des couches épitaxiales de meilleures qualités et surtout pour obtenir un dopage p plus efficace [I. Akasaki, 2002]. Cet événement a été l’une des étapes clés qui a révolutionnée cette technologie et a permis d’amorcer son intégration dans le milieu industriel.
Malgré l’avancé rapide qu’a connu le GaN et son potentiel pour la réalisation de sources optoélectroniques de haute efficacité, certains aspects de ce matériau restent encore mal maîtrisés, tels que la réalisation de contacts ohmiques avec une faible résistivité, ou encore le contrôle des interfaces métal/GaN et isolant/GaN. Les hétérostructures isolant/GaN sont généralement caractérisées par la présence d’une forte densité d’états de surface (D[indice inférieur it]). Cette forte D[indice inférieur it], aussi rapportée sur GaAs et sur d’autres matériaux III-V, détériore considérablement les performances des dispositifs réalisés et peut induire l’ancrage (‘pinning’) du niveau de Fermi. Elle constitue l’un des freins majeurs au développement d’une technologie MIS-GaN fiable et performante.
Le but principal de ce projet de recherche est l’élaboration et l’optimisation d’un procédé de passivation du GaN afin de neutraliser ou minimiser l’effet de ses pièges. Les conditions de préparation de la surface du GaN avant le dépôt de la couche isolante (prétraitement chimique, gravure, prétraitement plasma etc.), les paramètres de dépôt de la couche diélectrique par PECVD (pression, température, flux de gaz, etc.) et le traitement post dépôt (tel que le recuit thermique) sont des étapes clés à investiguer pour la mise au point d’un procédé de passivation de surface efficace et pour la réalisation d’une interface isolant/GaN de bonne qualité (faible densité d’états de surface, faible densité de charges fixes, bonne modulation du potentiel de surface, etc.). Ceci permettra de lever l’un des verrous majeurs au développement de la technologie MIS-GaN et d’améliorer les performances des dispositifs micro- et optoélectroniques à base de ce matériau. Le but ultime de ce projet est la réalisation de transistors MISFETs ou MIS-HEMTs de hautes performances sur GaN.
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Mondal, D. "Role of surface passivation and doping on the development of quantum dot solar cells." Thesis(Ph.D.), CSIR-National Chemical Laboratory, 2021. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/5988.
Full textAbstract:
The work in this thesis is focused on the use of advanced nanotechnology for the development of next-generation solar cells. Noble processes are developed to harness the unique optoelectronic properties of quantum dots to improve the performance of solar cells. This thesis explores the use of lead sulfide (PbS) quantum dots (QDs) as the main light-absorbing material for the development of QD solar cells. Near-infrared active and earth-abundant PbS QDs have emerged as a viable alternative to conventional materials (like Si solar cell, CIZS solar cell, etc.) due to their many distinct advantages, like solution-phase facile processability, bandgap tenability, and low material cost. Despite significant breakthroughs over the years, low performance has remained the major roadblock for the commercialization of QD solar cells. It has been understood that the primary reasons for the underperformance of QD solar cells are originated from not so high carrier mobility, low open-circuit voltage, and high charge recombination rate in QDs based solar cells. We posited that most of these drawbacks could effectively be mitigated by a comprehensive surface passivation strategy which would prohibit trap state formation and allow fast transport of photo carriers through the QD solids.
In this thesis, by understanding the surface chemistry of PbS QDs in detail, we have strategically developed the surface passivation methods to improve the power conversion efficiency (PCE) of QD solar cells. A low-temperature processed TiO2 layer (acts as an electron extracting layer in solar cell device) has been demonstrated to make QD solar cells on flexible substrates. The solvent induced 2D matrix layer has been tracked on the surface of QD ink. The 2D matrix layer thickness on the QD surface has been engineered to improve the PCE of QD solar cell. A two-step hybrid (organic and inorganic) ligand passivation strategy has been developed for the first time to make high quality QDs ink. Further, the one-step hybrid passivation method has been realized to develop QD solar cells. Through these strategic developments, in this thesis work, the PCE of PbS QD solar cell has been improved from 3.7% to 10.6%.
Lastly, based on the findings in this thesis work, possible future directions that could further improve the efficiency of QD solar cells are discussed.CSIR-National ChemicalLaboratory,Dr.HomiBhabhaRoad,Pune411008,India
AcSIR
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Arnoult, Daniel. "Caractérisation in situ par ellipsométrie et photoluminescence de l'interaction de plasmas multipolaires d’hydrogène et d'azote avec la surface (100) de GaAS." Lyon, INSA, 1986. http://www.theses.fr/1986ISAL0032.
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Le dépôt d'une couche de diélectrique sur GaAs entraîne généralement une forte densité d'états d'interface. Ceci exclue par conséquent toute technologie M. I. S. (Métal-Isolant-Semiconducteur) et peut conduire à des effets parasites dans les M. E. S. F. E. T. (Transistors à effet de champ barriére Shottkyy) tels que des courants de fuite. L ' origine de ces états n'est pas clairement connue mais les défauts de stœchiométrie (antisites,Arsenic libre) jouent très certainement un rôle important. Pour remédier à ces problèmes nous avons utilisé un schéma de passivation faisant appel à des traitements par plasmas multipolaires détériorant le moins possible la surface: -désoxydation par plasma d ' hydrogène ; -passivation par plasma d ' azote ; -dépôt diélectrique protecteur (Si3N4). Le travail effectué a d ' abord consisté en la conception et la mise au po1nt d'un dispositif expérimental (sas d’introduction- chambre nettoyage/ passivation-chambre dépôt diélectrique> en technologie ultravide. Le suivi et le contrôle des divers traitements a été rendu possible grâce aux mesures d'éllipsométrie et de photoluminescence in situ. Nous sommes ainsi parvenu : - d'une part à désoxyder complètement une surface de GaAs par un plasma d'hydrogène à 200"C, - d'autre part à améliorer les conditions de passivation lors des plasmas d'azote.
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Crowe, Loretta L. "Reversible Attachment of Organic Dyes to Silica Surface Through Meijer-Type Hydrogen Bonding." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14058.
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In an approach to creating molecular-scale structures on glass surfaces via self assembly, a strongly-dimerizing ureido-[2-(4-pyrimidone)] (UPy) quadruple hydrogen-bonding array was chemically immobilized on silica surfaces by way of a triethoxysilane functionality. The unreacted surface silanols were then thoroughly passivated with a monofunctional organosilane, resulting in isolated UPy binding sites on the glass surface. These binding sites were found to selectively bind the strongly fluorescent perylenediimide (PDI) functionalized UPy molecules from solution, thus non-covalently linking the fluorophore to the surface. The association between the self-complementary molecules was exceptionally strong, both in solution and at the surface, such that effective hydrogen-bonding was retained after most solvent treatments. The binding was also reversible, however, so that washes with polar protic and dipolar aprotic solvents with high hydrogen-bonding capabilities, such as water, alcohols, and DMSO, resulted in the removal of the non-covalently bound fluorophore-tagged UPy.
The UPy:UPy dimer system was also investigated in solution, using pyrene intramolecular excimer formation as a monitor of the dissociation of the pyrene heterodimers into homodimers incapable of forming excimers at micromolar concentrations. In addition, the energy transfer process in solution between pyrene and perylenediimide fluorophores linked through UPy dimerization was studied, with the intention using FRET-based measurements on the surface at single-molecule levels in order to determine the distances between UPy binding sites. Energy transfer was found to occur, but the observed photophysical behavior was complicated by possible secondary processes, which steady-state fluorescence measurements were unable to elucidate.
The benefit of using this UPy system for attaching molecules to a surface lies in its reversibility of binding and versatility in manner of molecules which van be retained on the modified surface with a strong association. In this way molecular-scale features could conceivably be constructed on a surface by self-assembly, with the option of further chemical reactions to lock them in place, thus creating structures beyond the accessibility range of the conventional lithographic methods.
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Hwang, Gyuweon. "Surface trap passivation and characterization of lead sulfide quantum dots for optical and electrical applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98741.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-119).
Quantum dots (QDs) are semiconductor nanocrystals having a size comparable to or smaller than its exciton Bohr radius. The small size of QDs leads to the quantum confinement effects in their electronic structures. Their unique optical properties, including a tunable emission from UV to IR, make QDs attractive in optoelectronic applications. However, further improvements in device performance are required to make them competitive. One well-known factor that presently limits the performance of QD thin film devices is sub-band-gap states, also referred to as trap states. For instance, trap states impair optical properties and device performance by providing alternative pathways for exciton quenching and carrier recombination. Chemical modification of QDs has been commonly used for passivating trap states and thereby improving QD devices. However, the influence of chemical modifications of ligands, QD surfaces, or synthetic routes on electrical properties of QD thin films is not sufficiently characterized. Suppressing the trap states in QD thin films is a key to improve the performance of QDbased optoelectronics. This requires fundamental understanding of trap state source, which is lacking in these materials. In this thesis, I pursue to find a systematic method to control density of trap states by exploring different characterization techniques to investigate trap states in QD thin films. These attempts provide insight to develop a rationale for fabricating better performing QD devices. This thesis focuses on the trap states in IR emitting lead sulfide (PbS) QD thin films, which have great potential for application in photovoltaics, light emitting diodes (LEDs), photodetectors, and bio-imaging. Previously, QD thin films are treated with different ligands to passivate trap states and thereby improve the device performance. Through my work, I pursued to unveil the electrical characteristics and chemical origin of trap states, and develop a strategy to suppress the trap states. First, I hypothesize that surface dangling bonds are a major source of trap states. An inorganic shell layer comprised of cadmium sulfide (CdS) is introduced to PbS QDs to passivate the surface states. Addition of CdS shell layers on PbS QDs yields an enhanced stability and quantum yield (QY), which indicates decreased trap-assisted exciton quenching. These PbS/CdS core/shell QDs have a potential for deep-tissue bio-imaging in shortwavelength IR windows of 1550-1900 nm. However, the shell layer acts as a transport barrier for carriers and results in a significant decrease in conductivity. This hinders the incorporation of the core/shell QDs in electrical applications. An improved reaction condition enables the synthesis of PbS/CdS QDs having a monolayer-thick CdS shell layer. These QDs exhibit QY and stability comparable to thick-shell PbS/CdS QDs. Incorporation of these thin-shell QDs improves external quantum efficiency of IR QD-LEDs by 80 times compared to PbS core-only QDs. In the second phase of my work, I explore capacitance-based measurement techniques for better understanding of the electrical properties of PbS QD thin films. For in-depth analysis, capacitance-based techniques are introduced, which give complementary information to current-based measurements that are widely used for the characterization of QD devices. Nyquist plots are used to determine the dielectric constant of QD films and impedance analyzing models to be used for further analysis. Mott-Schottky measurements are implemented to measure carrier concentration and mobility to compare PbS core-only and PbS/CdS core/shell QD thin films. Drive-level capacitance profiling is employed to characterize the density and energy level of trap states when QD films are oxidized. Lastly, I investigate the chemical origin of trap states and use this knowledge to suppress the trap states of PbS QD thin films. Photoluminescence spectroscopy and X-ray photoelectron spectroscopy show that standard ligand exchange procedures for device fabrication lead to the formation of sub-bandgap emission features and under-charged Pb atoms. Our experimental results are corroborated by density functional theory simulation, which shows that the presence of Pb atoms with a lower charge in QDs contributes to sub-bandgap states. The trap states generated after ligand exchange were significantly reduced by oxidation of under-charged Pb atoms using 1,4-benzoquinone. The density of trap states measured electrically with drive-level capacitance profiling shows that this reduces the electrical trap density by a factor of 40. In this thesis, I characterized trap states and showed that by suppressing the trap states we can modify the electrical properties of QD thin films, which influence the performance of QD devices directly. This work is a starting point to fully analyze the trap states in QD thin devices and thereby provides insight to design a rationale for fabricating better performing QD devices.
by Gyuweon Hwang.
Ph. D.
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DELIDAIS, ISABELLE. "Defauts de volume et de surface dans le silicium pour applications photovoltaiques : microanalyse, proprietes, passivation." Paris 11, 1991. http://www.theses.fr/1991PA112295.
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Ce travail porte sur les comportements physico-chimiques et electriques de l'oxygene, de l'hydrogene et des impuretes metalliques, dans du silicium de type p pour applications photovoltaiques. La premiere partie concerne le travail theorique effectue sur la modelisation de l'efficacite de collecte mesuree par ebic. Dans une seconde partie, les analyses sims et l'utilisation d'un traceur (#1#8o) nous ont permis d'acceder aux coefficients de diffusion de l'oxygene, a 1000 et 800c, dans du silicium fz, cz et polyx et de mettre en evidence la presence d'oxygene largement au-dela de sa limite de solubilite a 1000c. Cette sursaturation est due en partie a des precipites riches en oxygene, decores de deuterium apres traitement par plasma radiofrequence. La presence de ces precipites d'oxygene explique la faible efficacite de collecte de ces echantillons. Pour le polyx, plus les recuits (sous vide ou sous oxygene) sont realises a temperatures elevees, plus la longueur de diffusion des porteurs minoritaires est faible. Les analyses sims et xps indiquent que le cuivre vient se pieger sur les precipites d'oxygene. Cet effet gettering est plus efficace pendant l'oxydation. Par ailleurs, la couche d'oxyde constitue une barriere pour la diffusion du deuterium. L'analyse des resultats c(v) indique que l'hydrogene interagit avec le dopant et le passive. Dans ce cas, il n'est pas possible d'utiliser notre modele ebic. Nous avons pu egalement observer que le plasma d'hydrogene degrade les proprietes electroniques de la surface alors qu'il passive les defauts de volume electriquement actifs pour le polyx
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Narasimha, Shreesh. "Understanding and application of screen-printed metallization, aluminum back surface fields, and dielectric surface passivation for high-efficiency silicon solar cells." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/16453.
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Benhachoum, Mohamed. "Interaction d'ions multichargés avec des surfaces de diamant, de graphite et de silicium." Paris 6, 2004. http://www.theses.fr/2004PA066407.
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Lapeyrade, Mickael. "Utilisation des plasmas micro-ondes RCE pour préparer des films minces de nitrure de silicium : Application à la passivation des matériaux GaInAs et AlInAs." Ecully, Ecole centrale de Lyon, 1999. http://bibli.ec-lyon.fr/exl-doc/TH_T1801_mlapeyrade.pdf.
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Cette étude démontre la possibilité de déposer, à basse température (200-300°C) et avec une puissance micro-onde limitée (220 W), des films de nitrure de silicium de qualité électronique (résistivité de 1015 Q. Cm) avec des propriétés physico-chimiques proches du nitrure de silicium stœchiométrique élaboré à haute température, et qui soit compatible avec une technologie de passivation de matériaux III-V. Des mesures par sonde de Langmuir ont permis de caractériser le plasma d'azote dans les conditions expérimentales utilisées. Une étude approfondie des propriétés électriques, structurales et physico-chimiques des films montre que les propriétés des films sont très dépendantes des paramètres de la source RCE et de la nature du substrat initial. Un procédé de passivation a été défini. Les traitements de surface combinent désoxydation chimique en voie humide et nitruration en voie sèche. Le dépôt de nitrure de silicium peut être réalisé depuis la température ambiante jusqu'à 300°C. Une étude des propriétés physico-chimiques et électriques des interfaces Si3N4/AlInAs et Si3N4/GaInAs a été réalisée. La préparation de surfaces idéales à partir de surfaces "technologiquement contaminées" et d'interfaces Si3N4/AlInAs et Si3N4/GaInAs de qualité à partir de surfaces vierges ou de surfaces technologiques, est délicate à optimiser, notamment en raison de la présence d'arsenic élémentaire, source d'états d'interfaces. Ce procédé de passivation a été appliqué avec succès sur des transistors HEMT et des photodiodes de la filière InGaAlAs/InP. Il est actuellement utilisé de façon courante au laboratoire pour passiver les composants optoélectroniques de type photodiodesIn this work, we present the possibilities of a low power (< 250W) compact ECR (Electron Cyclotron Resonance) source to produce, at low deposition temperature (< 300°C), high quality SiNx films compatible with III-V semiconductor devices. Nitrogen plasma and pure silane have been used as gas precursors. We have studied the effect of varying the main process parameters on the composition and properties of the films. The deposited films have been characterized in-situ by X-ray Photoelectron Spectroscopy (XPS) and Spectroellipsometry and ex-situ by FTIR, Nuclear Reaction Analysis (NRA) and Energy Recoil Detection Analysis (ERDA), and finally I-V and C-V measurements. Each parameter has an optimal range of values or a threshold value necessary to obtain films with high dielectric quality. For a deposition temperature of 300°C, the best films exhibit a resistivity of 1015 Q. Cm and a breakdown voltage of 3 MV. Cm-1. The physicochemical properties of the films are close to those of stoichiometric silicon nitride. Strong correlations have been observed between the physicochemical and the electrical properties of the films, over the entire range of process parameters. A passivation process, based on surface treatments, oxide removal in solution, plasma nitridation and SiNx ECR plasma deposition, has been developed. The chemical and electrical properties of SiNx/AlInAs, SiNx/GaInAs and SiNx/InP interfaces have been investigated. Clean optimized surfaces appeared critical to achieve, mainly due to the existence of residual oxides and elemental arsenic at the interface, which is known to generate interface states. We have investigated the nitridation of non contaminated surfaces (i. E. Freshly grown by MBE without any contact with the atmosphere) and evaluated the materials and plasma process limitations. HEMT devices and InGaAlAs/InP based photodiodes have been successfully passivated using the previously defined passivation process
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Chave, Jacques. "Passivation de la surface de l'InP par des éléments de la colonne V pour structures MIS." Ecully, Ecole centrale de Lyon, 1987. http://www.theses.fr/1987ECDL0001.
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Burrows, Michael Z. "Role of silicon hydride bonding environment in alpha-silicon hydrogen films for c-silicon surface passivation /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 152 p, 2008. http://proquest.umi.com/pqdweb?did=1654501711&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Chave, Jacques. "Passivation de la surface de l'InP par des éléments de la colonne V pour structures MIS." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37603864j.
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Michalak, David Jason. "Physics and Chemistry of Silicon Surface Passivation." Thesis, 2006. https://thesis.library.caltech.edu/1679/1/ThesisMasterFinal.pdf.
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Low interfacial electron-hole recombination rates are essential for low-noise electronic devices and high-efficiency solar energy converters. This recombination rate is dependent on both the surface electrical trap state density, NT,s, and the surface concentrations of electrons, ns, and holes, ps. A reduction in NT,s is often accomplished through surface chemistry, and lower recombination rates, through lower NT,s values, have been demonstrated in this work for surfaces chemically treated to produce methoxylated, Si-O-CH3, overlayers. The H-Si(111) surfaces can react with methanol quickly in the presence of an oxidant or slowly in neat anhydrous methanol. Mechanisms have been proposed for both reactions.
Low recombination rates can also be achieved through control of the surface physics; a large ns or ps can lower recombination rates. To date, low recombination rates have often been attributed only to a reduction in NT,s, without a direct measurement of ns and ps, partly because the importance of ns and ps has not been fully recognized and partly because an accurate evaluation of ns and ps can be very difficult. Surface recombination rates of silicon immersed in liquids containing various redox species (e.g., Fc+/0, I2, Me10Fc+/0, or CoCp2+/0) were studied using an rf photoconductivity decay apparatus and compared with ns and ps values obtained from Mott-Schottky and other analysis techniques. The results demonstrate that the observed recombination rates can only be correlated with NT,s values when ns [approx.] ps. In all other cases, the recombination rate was low due to a large ns or ps even for surfaces with large NT,s values.
The full impact of this work was further realized through a study of the recombination rates of H-Si immersed in solutions of 48% HF, 40% NH4F, and buffered HF (BHF), because such measurements are often performed for in situ monitoring of the surface quality during wafer processing steps. Our results demonstrate that only HF contacts can be used for in situ monitoring because ns [approx.] ps. For NH4F or BHF contacts, low recombination rates were observed only because ns » ps, and NT,s cannot be inferred from these measurements.
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Chen, Chang Ming, and 陳昶名. "Silicon Surface Passivation with ALD Al2O3 Dielectric Film." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/82076286337608288790.
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碩士國立清華大學
材料科學工程學系
103
The surface to volume ratio is increasing due to the cost-driven reduction of the solar cell thickness thickness, which makes surface passivation a decisive factor for the final solar cell efficiency. Al2O3 have a high dielectric constant as a dielectric layer and have sufficient build-in nagative fixed oxide charge which generates an electric field. This field effect prevent the chances of minority carrier recombine at the surface which can greatly enhance the surface passivation. Meanwhile Atomic Layer Deposition (ALD) coating technology is developing rapidly in recent years, a film thickness can precisely control by number of cycles. Its good uniformity characteristics and an excellent aspect ratio so that today many companies used in the film manufacturing process. In this study, different thickness of ALD Al2O3 under different annealing conditions and PECVD SiNx are plated on n type Si wafers to examine the passivation effect. After that the samples are made into MOS structure to get the high-frequency capacitance-voltage data. The calculation of the doping concentration of the silicon substrate, the depletion zone width, the flat band voltage and fixed oxide charge will be found. The results show that annealing treatment and high temperature PECVD lead Al2O3 fixed oxide charge change from positive into negative, then the field effect passivation has improved significantly which is also reflected in the PCD effective carrier lifetime measurement of results and for covering the SiNx. The trend of lifetime and fixed oxide charge density versus different thickness of ALD Al2O3 are the same. This explains the good passivation effect is due to more fixed oxide charge in oxide layer. In addition, we observe that there are blisters generated at film surface. With increasing film thickness and number of heat treatment density blister appeared also increases but no direct effect on the effective carrier lifetime results.
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Lin, Tzung-Han, and 林宗翰. "Silicon nanoelectronic sensors with SAMs selective surface passivation." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/01757342341900179060.
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碩士國立交通大學
材料科學與工程學系奈米科技碩博士班
101
In this study, selective ablation of self-assembly monolayer methoxy-poly (ethylene glycol) silane (MPEG-sil) and Octadecyltrichlorosilane (OTS) on silicon nanoelectronic devices by localize joule heating was demonstrated for biosensing application. Lightly doped region in a silicon nanoelectronic device is usually functioned as the active channel which is sensitive to the change of surface potential. And, the resistance of this region is higher compared to other regions in a device so that the electric power consumed. SAMs on lightly doped region were ablated during Joule heating leaving the rest area passivated. The subthreshold swing of nanoelectronic device almost kept unchanged after Joule heating. AFM was adopted to characterize the device surface before and after Joule heating and selective biomolecule modifications. Analysis of fluorescent results showed consistency with AFM results that selectivity in surface modofications was achieved. We found that SAM-ablated device possess potential in the increase of sensing response and in the increase of sensitivity for low concentration detection. In streptavidin detection, the device with selective modification exhibited a detection limits of 15 pM, while the device without selective modification showed an order of magnitude higer in its limit of detection.
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Tsai, Meng-Han, and 蔡孟翰. "Surface Passivation on N-type Silicon Solar Cells." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/41704707508113103834.
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碩士國立臺灣大學
電子工程學研究所
100
Wafer based solar cell accounts for the production of a large part in photovoltaic industry due to its stability and high efficiency. Although the technology of wafer based solar cell has been well-developed for conventional structure, there are still numerous new challenges existing for the high efficiency solar cell. In this thesis, the fabrication process of n-type crystalline silicon solar cell is demonstrated by using ion implantation to form the boron (p+) emitter and phosphorous (n+) back surface field. By means of appropriate annealing, the implanted dopants could be activated, and the damage caused by the implantation can be repaired. Moreover, surface passivation plays an important role in promoting the efficiency of cells due to its strong dependence of open circuit voltage (Voc). Therefore, the mechanism and characteristic of surface passivation were introduced in this work. Then, different passivation layers were designed and analyzed by quasi-steady-state photoconductance and photoluminescence (QSSPC) measurement. In this work, the SiNx/Al2O3 stack layers could provide the best passivation quality. And with the excellent passivation of SiNx/Al2O3 stack layers, efficiency more than 18% is shown in this work.
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Lin, Cheng-Yu, and 林政宇. "Study and Analysis of Passivation on GaSb Surface." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/q786sh.
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童韻樺. "Silicon Surface Passivation with ALCVD HfO2 Dielectric Thin Film." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/25921892868614694052.
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Mitchell, Jonathon Drew. "Application of amorphous silicon for photovoltaic silicon surface passivation." Phd thesis, 2011. http://hdl.handle.net/1885/151789.
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In recent years, the application of hydrogenated amorphous silicon (a-Si:H) to crystalline silicon (c-Si) solar cells for the purpose of surface passivation has begun to move rapidly forward following early innovations by Sanyo. The bulk of the research conducted throughout this thesis has been performed prior to this new drive in the development of a-Si:H/c-Si devices. Understanding the underlying principles and the essential physics concerning the interaction of these two materials has been often overlooked, making further improvements difficult, and limiting new technological developments therein. In this light, the strategies towards merging a-Si:H with c-Si to achieve high{u00AD} efficiency, low-cost photovoltaics are studied in this thesis, with a focus on the interface and lowering interface states.
Plasma-Enhanced chemical vapour deposition (PECVD) of a-Si:H has commonly been an effective method for achieving uniform coverage of the c-Si surface. However, many deposition parameters have been reported as optimal, stemming from the limited range of experimental conditions examined. In this study, a more complete range of deposition conditions are tested, with the nature of the a-Si:H across a broad array of parameters being investigated. Ideally, a-Si:H layers which are most likely to result in high quality surface passivation should be deposited using temperatures of 225{u00B0}C, applied rf-power at 4W (SlmW/cm{u00B2} ), and partial pressure of 650mT. Notably, the ranges for deposition that can be ideally utilised, are with temperatures between 200{u00B0}C and 250{u00B0}C, rf-power up to 8W (100mW/cm{u00B2}), and partial pressures between 400mT and 750mT. Although the ideal values are somewhat system specific, these broader ranges are common to many PECVD systems.
Previously overlooked in many studies on a-Si:H and indeed most hydrogenated materials is the influence of hydrides on the surface passivation. A widespread belief is that layers hydrogen{u00AD} rich in their bulk are best for passivation, due to a plentiful source of hydrogen. Analysis of hydride density by IR-spectroscopy has revealed several interesting results which identify some misconceptions concerning surface passivation and the influence of hydrides. In particular, this thesis clarifies the function of the composition and distribution of hydrides throughout the layer and their influence on the quality of the surface passivation; the existence of bulk and interface regions within the a-Si:H layer; and the influence of deposition conditions on the composition and density of hydrides. Ideally, a hydride-rich interface region is shown to yield the most reliable results.
The diffusion of hydrogen from within the a-Si:H bulk towards the interface with c-Si at an energy of l.SeV has been a widely accepted mechanism governing surface passivation. However, experimental evidence to support this preferential diffusion through a high-defect material such as a-Si:H has been somewhat absent. In this work, an Arrhenius relationship between temperature and surface passivation is revealed, providing evidence that disputes the a-Si:H bulk-diffusion hypothesis in favour of a surface-diffusion mechanism at the a-Si:H/c-Si interface. The thermally activated surface passivation is shown to have energy of 0.7 {u00B1} O.leV, below that required for bulk diffusion or spontaneous release of hydrogen. From this experimental study, new insight into a surface-related transport model governing the passivation of the c-Si surface by hydrogen already present at or near the interface is presented in this thesis. Determined in this physical model, is the relationship between the likelihood of hydrogen diffusion across a c-Si surface and temperature.
Following from early experimentation using post-deposition thermal annealing to improve surface passivation by a-Si:H, a new plasma-enhanced chemical vapour deposition (PECVD) technique was developed as part of this work. Multi-Layer-PECVD involves the deposition of sub{u00AD} layers of a-Si:H with thermal cycling, to build up a total layer thickness. This technique of sub-layer deposition is shown to improve the control of hydride density, composition, surface coverage and reduce the inherent thin-film stresses for very thin a-Si:H layers. Comparison of layers deposited by ML-PECVD in-place of standard PECVD showed improved reliability and stability thanks to this new approach to deposition of a-Si:H.
With a greater understanding for the properties of a-Si:H in passivating c-Si and improvements in deposition technique, stacked a-Si:H structures which combine n-type or p-type a{u00AD} Si:H with a thin intrinsic a-Si:H layer in a HiT-like design are investigated from the perspective of passivating c-Si. Results here show that high-quality surface passivation can be maintained, with recombination velocities and saturation current densities at the c-Si surface as low as 3cms{u207B}{u00B9} and averaged below 30fA/cm{u00B2} respectively, which are equivalent to those achieved with SiOx and SiN layers.
In a world first application, the a-Si:H(i) and stacked a-Si:H layer structure have been applied in this thesis to the mc-Si surface; whereby, excellent surface passivation results are achieved using both n- and p-type mc-Si. Recombination velocities below lOOcms{u207B}{u00B9} using only a-Si:H(i) were reduced further to approximately 40cms{u207B}{u00B9} with stacked a-Si:H(i/n) or a-Si:H(i/n) layers, without a diffused emitter. In addition, low current saturation densities of 4.5 x 10{u207B}{u00B9}{u2074}Acm{u207B}{u00B2} and implied open{u00AD}circuit voltages of 670mV were achieved. In the case of 100{u03BC}m mc-Si, further reductions are shown to be possible, opening the doorway for simple, high-efficiency mc-Si based photovoltaic designs at low-cost.
The work in this thesis has yielded an improved understanding relating to a-Si:H/c-Si devices. Fundamental misconceptions concerning the hydrogen passivation mechanism, hydride content and configuration have been identified and a more accurate understanding has been proposed. Although many of the principles in the Sanyo HIT design have recently been reproduced by other groups, the implications of this research remain applicable. Importantly, the research regarding the optimisation of a-Si:H, development of ML-PECVD and many of the preliminary findings of this research are focused on high-efficiency, low-cost next generation photovoltaic designs yet to be developed.
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Tsu, Tsung Andrew Li. "Surface Passivation of Crystalline Silicon by Sputtered Aluminium Oxide." Phd thesis, 2010. http://hdl.handle.net/1885/7369.
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Efficient and inexpensive solar cells are necessary for photovoltaics to be widely adopted for mainstream electricity generation. For this to occur, the recombination losses of charge carriers (i.e. electrons or holes) must be minimised using a surface passivation technique suitable for manufacturing. In the literature, it has been shown that the aluminium oxide films are negatively charged dielectrics that provide excellent surface passivation of silicon solar cells. Meanwhile, sputtering has been shown to be an inexpensive thin film deposition method that is suitable for manufacturing. This thesis work aims to combine the excellent passivation properties of aluminium oxide with the manufacturing advantages offered by sputtering.
We show - for the first time - that sputtering is capable of depositing negatively charged aluminium oxide films that provide very good surface passivation of crystalline silicon. Effective surface recombination velocities of 24.6 cm/s and 9 cm/s are achieved on 0.8 Ohm.cm p-type crystalline silicon and 1 Ohm.cm n-type crystalline silicon respectively, with charges in the range of -1E11 to -1E13 per square centimetre. We specify the sputtering requirements and processing conditions required for achieving these results, showing the effect of the various deposition and annealing parameters. After investigating the physical characteristics of the sputtered aluminium oxide films using thin film measurement techniques such as Rutherford Backscattering Spectrometry and Secondary Ion Mass Spectroscopy, we conclude that the current levels of surface passivation attained using aluminium oxide films appear to be closely related to the interfacial layer and the presence of hydrogen. In some cases the level of surface passivation is most likely limited by the incorporation of unwanted impurities. We determine the composition and bonding of aluminium oxide films, discussing their significance to the various hypotheses concerning the origin of the negative charge. Finally, we demonstrate that sputtered aluminium oxide can be applied to solar cells by fabricating passivated emitter and rear cells with efficiencies as high as 20%. The results of this thesis provide the foundation for the sputtered aluminium oxide technology and its application to industrial solar cells.
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Lunt, Sharon Ruth. "Electrochemical, photoluminescence, and surface studies of the passivation of surface recombination processes on chemically treated gallium arsenide surfaces." Thesis, 1992. https://thesis.library.caltech.edu/6643/1/Lunt_sr_1992.pdf.
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This thesis describes work that has been done to study the chemical properties of GaAs surfaces relating to recombination processes. A variety of electrochemical, photoluminescence, and surface techniques have been used to study the mechanism an chemistry of the reduction of surface recombination in GaAs exposed to transition metal ions and complexes, and GaAs exposed to sulfur-containing molecules.
Electrochemical studies done on polycrystalline n-GaAs/liquid junctions treated with a variety of transition metal ions to study the mechanism of the observed improvement in I-V properties of GaAs(M3^(+))/Se^(-/2-)-KOH photoelectrochemical cells showed that the primary route is electrocatalysis. X-ray photoelectron spectroscopy (XPS) and extended x-ray adsorption fine structure (EXAFS) studies were performed on single crystal GaAs with Co, Ru and Cr ammines in order to determine the surface binding chemistry of the transition metals.
Steady state and time resolved and photoluminescence studies were done on GaAs surfaces exposed to sodium sulfide and a variety of organic thiols, alcohols and ammines. Unlike the transition metal ions, these types of complexes are shown to affect the cross section of surface recombination sites as determined by photoluminescence experiments. XPS studies were also done to correlate the observed changes in photoluminescence yield and lifetime with changes in surface chemistry.
Finally, some work has been done on an entirely different semiconductor system in order to explore the surface reactivity of a semiconductor surface at a more fundamental level. Several different types of metal dichalcogenides were exposed to strong Lewis acid complexes, and the surface chemistry was followed by XPS. These studies showed that there is a marked difference in the reactivity of metal dichalcogenide surfaces, which can be predicted from the known electronic structure of the conduction bands.
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Salivati, Navneethakrishnan. "Influence of surface passivation on the photoluminescence from silicon nanocrystals." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-08-1533.
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Although silicon (Si) nanostructures exhibit size dependent light emission, which can be attributed to quantum confinement, the role of surface passivation is not yet fully understood. This understanding is central to the development of nanocrystal-based detectors. This study investigated the growth, surface chemistry, passivation with deuterium (D2), ammonia (ND3) and diborane (B2D6) and the resulting optical properties of Si nanostructures.
Si nanocrystals less than 6 nm in diameter are grown on SiO2 surfaces in an ultra high vacuum chamber using hot-wire chemical vapor deposition and the as grown surfaces are exposed to atomic deuterium. Temperature programmed desorption (TPD) spectra show that that the nanocrystals surfaces are covered by a mix of monodeuteride, dideuteride and trideuteride species. The manner of filling of the deuteride states on nanocrystals differs from that for extended surfaces as the formation of the dideuteride and trideuteride species is facilitated by the curvature of the nanocrystal. No photoluminescence (PL) is observed from the as grown unpassivated nanocrystals. As the deuterium dose is increased, the PL intensity also begins to increase. This can be associated with increasing amounts of mono-, di- and trideuteride species on the nanocrystal surface, which results in better passivation of the dangling bonds and relaxing of the reconstructed surface. At high deuterium doses, the surface structure breaks down and amorphization of the top layer of the nanocrystal takes place. Amorphization reduces the PL intensity. Finally, as the nanocrystal size is varied, the PL peak shifts, which is characteristic of quantum confinement.
The dangling bonds and the reconstructed bonds at the NC surface are also passivated and transformed with D and NDx by using deuterated ammonia (ND3), which is predissociated over a hot tungsten filament prior to adsorption. At low hot wire ND3 doses PL emission is observed at 1000 nm corresponding to reconstructed surface bonds capped by predominantly monodeuteride and Si-ND2 species. As the hot wire ND3 dose is increased, di- and trideuteride species form and intense PL is observed around 800 nm that does not shift with NC size and is associated with defect levels resulting from NDx insertion into the strained Si-Si bonds forming Si2=ND. The PL intensity at 800 nm increases as the ND3 dose is increased and the intensity increase is correlated to increasing concentrations of deuterides. At extremely high ND3 doses PL intensity decreases due to amorphization of the NC surface. In separate experiments, Si NCs were subjected to dissociative (thermal) exposures of ammonia followed by exposures to atomic deuterium. These NCs exhibited size dependent PL and this can be attributed to the prevention of the formation of Si2=ND species.
Finally, deuterium-passivated Si NCs are exposed to BDx radicals formed by dissociating deuterated diborane (B2D6) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of low temperature peaks, which can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination.text
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Wang, Chun-Miin, and 王純敏. "Research on surface passivation and surfurization of CuInSe2 thin films." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/36706426821116079044.
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碩士國立中山大學
材料科學研究所
90
For improving the energy conversion efficiency of solar cells, it is essential to reduce the surface recombination velocity of CuInSe2 absorber layer. The use of quaternary alloys with an increasing band gap gradient was also demonstrated to be effectively increased the open-circuit voltage of the cells. The experiments using different concentration ammonium sulfur solutions to proceed surface passivation and sulfurization of CuInSe2 and CuInSe2：Sb films have been conducted to evaluate their influences on the band gap and other related properties. The band gaps of Cu-rich and In-rich CuInSe2 films did not change after ammonium sulfur treatment. For CuInSe2：Sb films after immersing (NH4)2Sx solution, the PL spectra gave an evidence of the formation of the quaternary CuInSxSe2-x alloys. The metal contacts to CuInSe2 films with the structures of Mo/P-type CuInSe2/Al and Mo/N-type CuInSe2/Au had been fabricated. Their I-V characteristics indicate that the Schottky Contacts had been successfully formed.
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Hsu, Chen-Wan, and 徐禎婉. "Surface Passivation of Silicon, Germanium, and Cu(In,Ga)Se2." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/86166572182604351320.
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碩士國立臺灣大學
光電工程學研究所
98
In this thesis, surface passivation of silicon, photoluminescence of silicon and germanium with various passivation layers, and enhancement of photoluminescence from Cu(In,Ga)Se2 with Al2O3 passivation are discussed. The effective passivation needs low interface trap density at the interface between passivation layer and Si, and ionized charges for field effect passivation. The thermal oxide (SiO2) with low interface defect density seems most effective but requires high growth temperature (900 ℃). Al2O3 with trapped negative fixed charges can serve as the field effect passivation. Moreover, doped amorphous Si can also have the field effect passivation with the controlled ionized charge density. The effective lifetime is measured by quasi-steady-state photoconductance (QSSPC). Photoluminescence (PL) measurement is consistent with QSSPC. The dependence of PL intensity on surface recombination velocity is theoretically studied. The passivation of a-Si becomes less effective after crystallization at high temperature annealing, indicating the larger bandgap is necessary. The GeO2 passivation on Ge seems effective and relative light intensity with 457nm laser by pumping is a little stronger than 671nm. CIGS solar cells have attained efficiencies above 19% and can be made with a number of different manufacturing techniques. Photoluminescence (PL) spectroscopy is a useful technique to analyze defects in semiconductor. Photoluminescent properties of such films depend strongly on their stoichiometry. The PL emission is explained in terms of two type transitions: donor–acceptor-pair (DAP) recombination at low temperatures and moderate excitation powers, and the band-impurity (BI) recombination involves electrons in conduction band to acceptor levels at high temperatures or high excitation power. Through the simulation we can connect with the relationship of surface recombination velocity and carrier concentration. Al2O3 seems effective passivation reduces interface defect of CIGS. Therefore, light intensity is enhancement from PL measurement.
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Lan, Maw Shyan, and 藍茂賢. "Analysis of surface passivation with (NH4)2Sx treatment on In0.5Ga0.5P." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/28516837434204004624.
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Qiu, Xian-Cheng, and 邱顯丞. "The effect of microchannel surface passivation on polymerase chain reaction." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/92749640475149552504.
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碩士國立屏東科技大學
生物機電工程系所
102
The polymerase chain reaction (PCR) is a technique that can duplicate specific DNA fragments, however, conducting the technique requires the use of a very large-scale thermal cycler. In order to accommodate for this problem, this study has developed a continuous flow PCR chip. Initially, CFD-ACE+TM commercial simulation software is used to simulate the impact that the three temperature zones configured in this paper have on the chip. After confirming the temperature distribution, microfuidic channels can be added to the simulations in order to investigate the feasibility and related parameters of the apparatus. In the experimentation, initially, a microelectromechanical processing technique and polydimethylsiloxane (PDMS) formwork technique were used to create a chip with microfuidic channels. For the temperature, on the two sides of the bottom of the chip, two heating modules were configured with different temperatures and a cooling zone was set up in the center to allow the thermal energy to transfer to the heat dissipation zone and allow the temperature of the chip’s center to decrease. The temperature control was composed of an 8051 single chip and temperature measurement device, which, the actual detection of wafer temperature was found to have the chip temperature difference between the inside and outside within 7-8K, Thus the use of this result with infrared thermal imager, by using the abovementioned conditions, could create three stable temperature zones. After successfully establishing the environment necessary for the PCR, optimization was conducted on the surface of the chip’s microfluidic channels. This paper used three types of surface passivation reagents to conduct comparisons and discovered that when the polysorbate 20 (Tween 20) has a concentration of 20%, it can significantly reduce the methyl (CH3) spectroscopy on the PDMS surface, resulting in an average surface roughness which is approximately 61nm. This outcome was significantly more favorable than the other two types. Also, as all the reagents used are water soluble, deionized water was used to conduct observations, and it was discovered that the Tween 20 can cause the PDMS to become hydrophilic; thus it can be seen that the Tween 20 has the optimal passivation effect. Furthermore, when applied to actual biological experiments, the results indicated that the apparatus successfully duplicated the DNA fragments and that use of passivation treatment can effectively help the response of the DNA copies. The experimental time was 50 min.Then for the device to explore, discover traffic 1μl/min and the sample volume at the time of 10μl or more, although not comparable to commercially available PCR thermal cycler, but no matter the time or the experimental results, the best able to reach a balance. Keywords：Continuous fluid PCR、Microfluidic chip、Polymerase chain reaction、Passivation、PDMS
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Lee, Ken-Hsuan, and 李耿亘. "Surface Passivation of Germanium Wafers using Hydrogenated Amorphous Silicon Layers." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/66857266560171042056.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
102
In this paper, we studied several important issues concerning fabrication of crystalline germanium (Ge) hetero-junction using amorphous Si as the passivation layers. First of all, surface cleaning procedure of Ge wafers was established through a comparison with the conventional RCA cleaning procedure for Si wafers. An efficient way for surface cleaning of Ge included a series of organic solvents, HCl, and HF treatments with suitable concentrations. Then, a surface oxide layer was fabricated with intention through an immediate dipping in H2O2 solution after HF treatment. Finally a very clean Ge(100) was obtained, which was verified by RHEED, by removing the oxide layer using thermal annealing in a high vacuum chamber at temperatures ranging 450 ℃. After surface cleaning process, we use PECVD to grow 16 nm hydrogenated amorphous silicon (a-Si:H) for germanium surface passivation. The best minority carrier lifetime of the Ge wafer after a-Si:H double-side coated was 291.3 μs, which was further reduced to 112.7 μs after completion of n+ a-Si:H/i a-Si:H/c-Ge/i a-Si:H/p+ a-Si:H.