@phdthesis{FelixDuarte2016, author = {Felix Duarte, Roberto}, title = {Analysis and optimization of interfaces in "wide-gap" chalcopyrite-based thin film solar cell devices}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-37402}, school = {BTU Cottbus - Senftenberg}, year = {2016}, abstract = {The chemical and electronic structure of chalcopyrite absorbers with different bulk band gap energies, Egbulk, [i.e., low-gap Cu(In,Ga)Se2 (CIGSe, Egbulk ~ 1.2 eV) and wide-gap CuInS2 (CIS, Egbulk ~ 1.5 eV)] and of buffer/absorber heterointerfaces based on these materials are studied with soft and hard x-ray spectroscopy techniques. Mechanisms that benefit (limit) the performance of low(wide)-gap chalcopyrite-based solar cells are identified. This knowledge is used to develop surface tailoring treatments to optimize buffer/absorber heterointerfaces based on wide-gap chalcopyrites and improve the performance of their solar cells. Photoemission spectroscopy (PES) characterization of the two absorbers (i.e., CIGSe and CIS) reveal compositional-depth profiles. The changes detected in CIGSe include: a near surface Ga-depletion, a strongly Cu-poor surface and a strong presence of surface Na that (likely) occupies Cu vacancies. A similar Cu-deficiency is found in CIS. The depth-composition changes result in significant widening of the band gap at the surface, Egsurf, (i.e., CIGSe, Egsurf: 1.70 ± 0.2 eV and CIS, Egsurf: 1.88 ± 0.2 eV) as evident by ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) measurements. Differences in the interaction of the CIGSe and CIS surfaces with deposited buffer materials are identified. PES and modified Auger parameter studies reveal strong intermixing at the CdS/CIGSe and ZnS/CIGSe heterointerfaces. S L2,3 x-ray emission spectroscopy (XES) measurements of CIGSe substrates submitted to CdS chemical bath deposition (CBD-CdS) treatments show the formation of In2S3 and defect-rich/nanostructured CdS at the interface, compounds with higher band gap values than the measured Egsurf for CIGSe. S L2,3 XES spectra of CIGSe substrates submitted to CBD-ZnS treatments reveal the formation of (Zn,In)(S,Se)2 chemical analogs at the interface. PES and XES measurement series show that the CdS/CIS heterointerface is more abrupt, with no detected interface chemical species. Direct measurement of the band alignment of these heterointerfaces reveals: an ideal conduction band offset (CBO) configuration for CdS/CIGSe (i.e., CBO: +0.11 ± 0.25 eV), a spike CBO configuration for ZnS/CIGSe (i.e., CBO: +1.06 ± 0.4 eV), and a highly unfavorable cliff CBO configuration for CdS/CIS (i.e., CBO: -0.42 ± 0.25 eV). The performance of solar cell devices based on these heterointerfaces is correlated to their CBO configuration. Two surface tailoring approaches intended to correct the CBO configuration of the CdS/CIS heterointerface are presented. One method is based on rapid thermal processing (RTP) selenization treatments of CIS absorbers, aiming to exchange Se for S in treated samples. The idea behind this approach is to modify the surface of a wide-gap chalcopyrite so that it forms a more favorable heterointerface with CdS, such as heterointerfaces within low-gap chalcopyrite devices. X-ray fluorescence analysis and PES measurements of RTP-treated CIS samples show a greater treatment effect at the surface of the sample compared to the bulk (i.e., surface [Se]/[S+Se] range: 0.23 ± 0.05 to 0.83 ± 0.05, compared to bulk [Se]/[S+Se] range: 0.01 ± 0.03 to 0.24 ± 0.03). Tuning of the Cu:In:(S+Se) surface composition from a Cu-poor 1:3:5 to a 1:1:2 stoichiometry is observed in RTP-treated CIS samples with lower to higher surface Se contents, respectively. UPS measurements show a shift in valence band maximum toward the Fermi level in samples with higher surface Se content (i.e., -0.88 ± 0.1 to -0.51 ± 0.1 eV), as expected for a reduction in Egsurf due to exchange of Se for S. Ultraviolet-visible spectrophotometry reveals a reduction in the optical band gap of samples with greater Se incorporation (i.e., from 1.47 ± 0.05 to 1.08 ± 0.05 eV), allowing for a working window for optimization purposes. The second tailoring method involves surface functionalization of CIS absorbers with dipole-charge-inducing self-assembled monolayers (SAM) of benzoic acid derivatives and thiol molecules. The introduction of dipole charges between a heterointerface can tune the relative alignment of the electronic bands composing its electronic structure; thus, use of a suitable dipole-inducing SAM could correct the CBO misalignment in the CdS/CIS heterointerface. UPS measurements of the secondary electron cut-off region of CIS samples treated with a selected set of SAMs show a work function modulation of CIS (i.e., 4.4 ± 0.2 eV - 5.2 ± 0.2 eV). Small gains in solar cell parameters of solar cells based on SAM-modified heterointerfaces are measured. An overview of the performance of chalcopyrite(kesterite)-based solar cells in relation to the electronic properties of their corresponding buffer/absorber heterointerface suggests that optimization approaches extending beyond the buffer/absorber heterointerface may be needed for further performance gains in wide-gap chalcopyrite-based solar cell devices.}, subject = {Photovoltaics; Thin Film Solar Cells; Chalcopyrite absorbers; Solid-state Physics; Photovoltaik; R{\"o}ntgenspektroskopie; D{\"u}nnschichtsolarzelle; Chalkopyrit-Absorbermaterialien; Festk{\"o}rperphysik; X-ray spectroscopy; Kupferkies; D{\"u}nnschichtsolarzelle; Festk{\"o}rperphysik; Fotovoltaik}, language = {en} } @phdthesis{Tavakoli2006, author = {Tavakoli, Mohammad Hossein}, title = {Numerical analysis of seeding process during Czochralski growth of oxide single crystals}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-145}, school = {BTU Cottbus - Senftenberg}, year = {2006}, abstract = {A series of two-dimensional and three-dimensional quasi-steady state numerical simulations have been performed for the initial stages (seeding process) of the Czochralski (CZ) growth of oxide crystals using the finite element method (FEM). We have considered different cases and configurations with respect to real systems in the CZ-dielectrics laboratory of the Institute for Crystal Growth (IKZ). Using induction heating in metallic parts as heat source the fluid flow and temperature field were determined in the whole CZ system. The aim of these calculations was to investigate and reveal the effect of several parameters such as the geometry and location of an active afterheater with respect to the crucible, arrangement and design of thermal insulation, crucible bottom shape, and seed rotation rate on the flow and temperature field of the system and the seed-melt interface shape. The results demonstrate that the temperature and fluid flow in the gas domain is strongly affected by an active afterheater and its insulation as well as their geometry and position. The results also show the important role played by the seed rotation rate for influencing the shape of the seed-melt interface.}, subject = {Kristallz{\"u}chtung; Czochralski-Verfahren; Czochralski-Verfahren; Ankeimprozess; Temperaturverteilung; Kristallz{\"u}chtung; Czochralski method; Seeding process; Heat transfer; Induction heating}, language = {en} } @phdthesis{Handick2016, author = {Handick, Evelyn}, title = {Surface and interface characterization by X-ray and electron spectroscopies - revealing the peculiarities of Cu(In,Ga)Se₂ chalcopyrite and CH₃NH₃PbI(₃-ᵪ)Clᵪ perovskite-based thin film solar cell structures}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-42431}, school = {BTU Cottbus - Senftenberg}, year = {2016}, abstract = {This thesis focuses on the investigation and characterization of the surfaces and interfaces of chalcopyrite-based Cu(In,Ga)Se₂ (CIGSe) and organo-metal mixed halide perovskites, specifically CH₃NH₃PbI(₃-ᵪ)Clᵪ thin film solar cell absorbers using various x-ray and electron spectroscopies. In particular, the impact of alkali treatments on the chemical and electronic surface and near-surface structure of CIGSe absorbers is studied. For CH₃NH₃PbI(₃-ᵪ)Clᵪ the compound formation is monitored and the peculiarities of the interface formation of CH₃NH₃PbI(₃-ᵪ)Clᵪ on compact and mesoporous TiO₂ are examined. Laboratory and synchrotron-based photoelectron spectroscopy are used to gain a depth-dependent picture of the chemical and electronic structure in the surface and near-surface region of CIGSe absorbers, focusing on the influence of NaF and NaF/KF post-deposition treatments (PDT) when compared to alkali-free CIGSe absorbers. The alkali-free and NaF-PDT absorbers show similar chemical properties, having a Cu and Ga poor surface region compared to the nominal bulk and the same chemical environment for indium and selenium. For the NaF/KF-PDT samples a K-In-Se compound is present on top of a Cu-In-Ga-Se compound, with a nanopatterned surface that is almost devoid of Cu and Ga. Further, for the NaF-PDT sample a near-surface electronic band gap of 1.61[+0.14/-0.51] eV is derived. In contrast, a large and more gradual change towards the surface is obtained for the NaF/KF-PDT absorber exhibiting a significant band gap widening of the surface, which is in agreement with a Cu- and Ga-devoid surface region and the formation of a K-In-Se surface compound. To in-situ monitor the compound formation of CH₃NH₃PbI(₃-ᵪ)Clᵪ on compact TiO₂ (c-TiO₂) hard x-ray photoelectron spectroscopy is used. During in-situ annealing a drop-casted layer of precursor solution on c-TiO₂ shifts in the perovskite related core levels can be observed upon reach the "transition temperature" of 80-100°C. Further the Cl signal decrease at the onset of annealing and shows a depletion in the surface region for annealing temperatures above 50°C. In addition, the chemical and electronic structure of the interface between perovskite and mesoporous TiO₂ (mp-TiO₂) or c-TiO₂ using different perovskite layer thicknesses are studied.}, subject = {Chalcopyrit; Perovskite; Photoelectron spectroscopy; Thin film solar cell; Chalkopyrite; Perowskite; Photoelektronenspektroskopie; D{\"u}nnschichtsolarzelle; Kupferkies; Perowskit; Photoelektronenspektroskopie; D{\"u}nnschichtsolarzelle}, language = {en} } @phdthesis{Dudek2011, author = {Dudek, Piotr}, title = {Atomic scale engineering of HfO2-based dielectrics for future DRAM applications}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-22775}, school = {BTU Cottbus - Senftenberg}, year = {2011}, abstract = {Modern dielectrics in combination with appropriate metal electrodes have a great potential to solve many difficulties associated with continuing miniaturization process in the microelectronic industry. One significant branch of microelectronics incorporates dynamic random access memory (DRAM) market. The DRAM devices scaled for over 35 years starting from 4 kb density to several Gb nowadays. The scaling process led to the dielectric material thickness reduction, resulting in higher leakage current density, and as a consequence higher power consumption. As a possible solution for this problem, alternative dielectric materials with improved electrical and material science parameters were intensively studied by many research groups. The higher dielectric constant allows the use of physically thicker layers with high capacitance but strongly reduced leakage current density. This work focused on deposition and characterization of thin insulating layers. The material engineering process was based on Si cleanroom compatible HfO2 thin films deposited on TiN metal electrodes. A combined materials science and dielectric characterization study showed that Ba added HfO2 (BaHfO3) films and Ti added BaHfO3 (BaHf0.5Ti0.5O3) layers are promising candidates for future generation of state of the art DRAMs. In especial a strong increase of the dielectric permittivity k was achieved for thin films of cubic BaHfO3 (k~38) and BaHf0.5Ti0.5O3 (k~90) with respect to monoclinic HfO2 (k~19). Meanwhile the CET values scaled down to 1 nm for BaHfO3 and ~0.8 nm for BaHf0.5Ti0.5O3 with respect to HfO2 (CET=1.5 nm). The Hf4+ ions substitution in BaHfO3 by Ti4+ ions led to a significant decrease of thermal budget from 900°C for BaHfO3 to 700°C for BaHf0.5Ti0.5O3. Future studies need to focus on the use of appropriate metal electrodes (high work function) and on film deposition process (homogeneity) for better current leakage control.}, subject = {Mikroelektronik; Miniaturisierung; Dielektrikum; Elektrode; Metall; Dielektrika; Hoch-k Materialien; Untersuchung auf atomarer Skala; Dielectrics; High-k materials; Atomic Scale Engineering; HfO2-based materials; XPS}, language = {en} } @phdthesis{Michling2013, author = {Michling, Marcel Frank}, title = {Spektroskopische Untersuchungen an organischen Materialien und Metalloxiden}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-29014}, school = {BTU Cottbus - Senftenberg}, year = {2013}, abstract = {Im Rahmen der vorliegenden Arbeit wurde mit Synchrotron-basierenden, optischen und Elektronen-basierenden Methoden die elektronischen Eigenschaften zweier unterschiedlicher Materialklassen untersucht. Der Fokus lag dabei im besonderen auf der Bestimmung der Größe der Bandl{\"u}cke/HOMO-LUMO-L{\"u}cke und ihre Abhängigkeit der verwendeten Methode. Die zwei unterschiedliche Materialklassen, welche untersucht wurden sind folgende: Erstens die organischen Systeme Cobalt-Phthalocyanin und Fulleren. An Ihnen wird der Einfluss der verwendeten Messmethoden aufgezeigt und die sich draus ergebenen HOMO- LUMO-L{\"u}cken (elektronisch, Volumen, Oberfläche, optisch) diskutiert. Es zeigt sich, dass die optische Methode (Ellipsometrie) generell den kleinsten Wert und die elektronischen Methoden (XPS, XAS) den größten Wert ergeben. Die Gr{\"u}nde daf{\"u}r werden ausf{\"u}hrlich diskutiert. Durch die Kombination von XPS- , XAS- und Ellipsometrie-Messungen war es möglich die Orientierung der aufgedampften CoPc-Molek{\"u}le auf den SiO2-Substrat zu bestimmen. Zweitens wurden die Metalloxide HfO2, Al2O3, In2O3 und Ga2O3 aufgrund ihrer großen technologischen Bedeutung untersucht. Mit Hilfe von ALD Zyklus-f{\"u}r-Zyklus Experimenten konnten die elektronischen Eigenschaften von HfO2 in Abhängigkeit der ALD- Zyklenzahl und das Wachstum von HfO2 in den ersten Zyklen studiert werden. Auf Basis der XPS- und EELS-Ergebnisse wurde ein Wachstumsmodell entwickelt. Es wird ebenfalls der Einfluss einer Dipolschicht an der Grenzfläche HfO2/SiO2 auf die Größe der Bandl{\"u}cke in den EELS-Messungen diskutiert. Mittels resonanten Photoemission wurde ein neuer Auger-Mechanismus (3-Loch-Auger-Prozess) in den Oxiden gefunden. Dieser hat seine Ursache in Defekten. Defekte f{\"u}hren auch zu einer Fano-Anti-Resonanz, welche an der O1s-Absorptions-Kante beobachtet und diskutiert wird.}, subject = {Spektroskopie; Metalloxide; Spektroskopie; Organik; Metalloxide; Bandl{\"u}cke; 3h-Auger; Spectroscopy; Organics; Metal oxides; Band gap; 3h-Auger}, language = {de} } @phdthesis{Calvet2002, author = {Calvet, Wolfram}, title = {Pr{\"a}paration und in-situ Charakterisierung MBE-gewachsener Kupferindiumdisulfid-Schichten}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-000000242}, school = {BTU Cottbus - Senftenberg}, year = {2002}, abstract = {Die vorliegende Arbeit behandelt CuInS2-Filme, die mittels Molekularstrahlepitaxie auf einkristallinen Si- und GaAs-Substraten unterschiedlicher Orientierung abgeschieden wurden. In-situ kamen dabei photoelektronenspektroskopische Analysemethoden und die Beugung niederenergetischer Elektronen zum Einsatz. Ex-situ wurden die Filme mittels R{\"o}ntgenstrukturanalyse, Ionenr{\"u}ckstreuung und Photolumineszenz untersucht. Zun{\"a}chst wurde die Bandanpassung des Si(111)/CuInS2(112)-Hetero{\"u}bergangs bestimmt, wobei die Grenzfl{\"a}che durch das Auftreten von Fremdphasen und durch Interdiffusion nicht ideal und stark gest{\"o}rt erscheint. Es wurde ein Grenzfl{\"a}chendipol von etwa 1 eV ermittelt. Der Vergleich der chemischen Zusammensetzung an der Filmoberfl{\"a}che und im Filmvolumen deutet auf einen Konzentrationsgradienten in der Schicht hin. Unabh{\"a}ngig vom Cu/In-Verh{\"a}ltnis wurde eine schwefelarme Oberfl{\"a}che gefunden. Zudem zeigen Cu-reiche CuInS2-Filme unabh{\"a}ngig von der Substratorientierung ein [112]-orientiertes Wachstum, wogegen im In-reichen Pr{\"a}parationsregime die Kristallorientierung des Substrates {\"u}bernommen wird.}, subject = {Kupferindiumsulfid; D{\"u}nne Schicht; Molekularstrahlepitaxie}, language = {de} } @phdthesis{Meier2004, author = {Meier, Ulrich}, title = {Grenzfl{\"a}chenverhalten und Morphologie des ZnO/Si-Heterokontaktes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-000000551}, school = {BTU Cottbus - Senftenberg}, year = {2004}, abstract = {Als Modellsystem f{\"u}r gleichrichtende Heterokontakte von D{\"u}nnschichtsolarzellen wurden polykristalline ZnO-Filme auf Si mittels Magnetron-Sputtern und metallorganischer Gasstrahldeposition (MOCBD) abgeschieden. Mit Photoelektronenspektroskopie wurden bis zu 3 chemische Grenzfl{\"a}chenkomponenten gefunden: SiOx, eine Willemit-artige Mischphase und reduziertes Zn0. Letzteres kann {\"u}ber die Sputterparameter Bias-Potenzial und O2-Partialdruck kontrolliert werden. Mit MOCBD wurden auf Si(111):H abrupte Heterokontakte pr{\"a}pariert. Ferner tritt an Korngrenzen und der Oberfl{\"a}che Hydroxid auf. Dies kann durch Heizen entfernt werden. W{\"a}hrend der Messungen traten energetische Verschiebungen der Spektren auf, die die Auswertung der Grenzfl{\"a}chenenergetik st{\"o}ren. Zur Erkl{\"a}rung wurde folgendes Modell entwickelt: In einem schnellen Oberfl{\"a}chenprozess findet Photolyse von Hydroxid statt, wodurch H2O oder mobile OH-Gruppen gebildet werden, die Sauerstoffvakanzen ausheilen und so die n-Dotierung vermindern. In einem langsameren Volumenprozess wird durch Photolyse von ZnO die n-Dotierung erh{\"o}ht.}, subject = {Silicium; Zinkoxid; Magnetronsputtern; MOCVD-Verfahren; Photoelektronenspektroskopie; ZnO; Si; Interface reaction; XPS; PES}, language = {de} } @phdthesis{Lupina2006, author = {Lupina, Grzegorz}, title = {Praseodymium Silicate high-k dielectrics on Si(001)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-421}, school = {BTU Cottbus - Senftenberg}, year = {2006}, abstract = {Aggressive scaling of the complementary metal-oxide-semiconductor (CMOS) transistors resulted in the silicon dioxide (SiO2) gate dielectrics being as thin as 1.2 nm in the state-of-the-art high performance transistors. In consequence, the leakage current due to direct tunneling of electrons through the gate oxide increased significantly resulting in an unacceptably high level of power dissipation. For this reason, it is very desirable to replace the SiO2 gate dielectric with an insulator of a higher dielectric constant (high-k). The higher dielectric constant allows for the use of physically thicker dielectric layers with high capacitance densities but strongly reduced tunneling currents. This work focuses on the preparation and characterization of Praseodymium silicate high-k dielectric layers on Si(001) and evaluates the potential of this material to replace SiO2 as a gate dielectric in the state-of-the-art and future CMOS technology generations.}, subject = {High-k dielectrics; Praseodymium silicate; XPS}, language = {en} } @phdthesis{Meyer2007, author = {Meyer, Moritz Andreas}, title = {Effects of advanced process approaches on electromigration degradation of Cu on-chip interconnects}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-3509}, school = {BTU Cottbus - Senftenberg}, year = {2007}, abstract = {This thesis provides a methodology for the investigation of electromigration (EM) in Cu-based interconnects. An experimental framework based on in-situ scanning electron microscopy (SEM) investigations was developed for that purpose. It is capable to visualize the EM-induced void formation and evolution in multi-level test structures in real time. Different types of interconnects were investigated. Furthermore, stressed and unstressed samples were studied applying advanced physical analysis techniques in order to obtain additional information about the microstructure of the interconnects as well as interfaces and grain boundaries. These data were correlated to the observed degradation phenomena. Correlations of the experimental results to recently established theoretical models were highlighted. Three types of Cu-based interconnects were studied. Pure Cu interconnects were compared to Al-alloyed (CuAl) and CoWP-coated interconnects. The latter two represent potential approaches that address EM-related reliability concerns. It was found that in such interconnects the dominant diffusion path is no longer the Cu/capping layer interface for interconnects as in pure Cu interconnects. Instead, void nucleation occurs at the bottom Cu/barrier interface with significant effects from grain boundaries. Moreover, the in-situ investigations revealed that the initial void nucleation does not occur at the cathode end of the lines but several micrometers away from it. The mean times-to-failure of CuAl and CoWP-coated interconnects were increased by at least one order of magnitude compared to Cu interconnects. The improvements were attributed to the presence of foreign metal atoms at the Cu/capping layer interface. Post-mortem EBSD investigations were used to reveal the microstructure of the tested samples. The data were correlated to the in-situ observations.}, subject = {Elektromigration; Elektromigration; Kupfer; Leiterbahn; In-situ; Gef{\"u}ge; Electromigration; Cu interconnects; In-situ; Cu microstructure}, language = {en} } @phdthesis{Lehmann2007, author = {Lehmann, Carsten}, title = {Elektronische Struktur d{\"u}nner Halbleiterfilme (Chalkopyrite) als Absorbermaterialien f{\"u}r D{\"u}nnschichtsolarzellen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-4319}, school = {BTU Cottbus - Senftenberg}, year = {2007}, abstract = {Ziel der Arbeit war es, erstmalig die Bandstruktur des in D{\"u}nnschichtsolarzellen verwendeten Absorbermaterials CuInS2 zu bestimmen. Zu diesem Zweck konnte ein neues GSMBE-Verfahren mit TBDS als Schwefel-Precursor etabliert werden, um die Verwendung von elementarem Schwefel in einem UHV-System zu ersetzen. Zus{\"a}tzlich zu den abgeschiedenen Schichten wurde eine Spaltfl{\"a}che pr{\"a}pariert. Die Charakterisierung der Proben erfolgte in situ mittels XPS/UPS und LEED. F{\"u}r weitere ex situ Untersuchungen standen XRD und SEM zur Verf{\"u}gung. Die ARUPS-Untersuchungen zur Bestimmung der Bandstruktur fanden unter Verwendung von Synchrotronstrahlung statt. Die aufgenommenen Bandstrukturen wurden mit Bandstrukturberechnungen Eyerts und Zungers verglichen. Dabei gestattete eine Zusammenarbeit mit Eyert eine exakte Verifizierung jenseits hochsymmetrischer Verl{\"a}ufe. CuInS2(001) und CuInS2(112) wurden auf Si und GaAs abgeschieden und zeigte Wachstumsraten, die im Vergleich mit MBE-Verfahren {\"a}lterer Arbeiten um bis zu 85 \% geringer waren. Dies f{\"u}hrte auf Si zur Ausbildung von CuSi-Phasen, so dass sich Si als Substrat in diesem Verfahren als ungeeignet erwies. Die CuInS2-Abscheidung auf GaAs zeigte eine starke Abh{\"a}ngigkeit von der vorhandenen Oberfl{\"a}chenrekonstruktion. Eine 2x1-Rekonstruktion auf GaAs(100) f{\"u}hrte zu einer terrassierten CuInS2-Schicht. Eine Abscheidung auf der 2x2-rekonstruierten GaAs(111)A-Oberfl{\"a}che hatte eine facettierte CuInS2-Oberfl{\"a}che zur Folge. Auf schwefelpassiviertem, rekonstruktionsfreien GaAs(111)B zeigte sich dagegen facettenfreies CuInS2(112)-Wachstum in vorherrschender Chalkopyrit-Struktur. An den Oberfl{\"a}chen von Cu-reichen CuInS2-Schichten bildeten sich CuS-Kristallite. Diese polykristallinen Ablagerungen f{\"u}hrten bei ARUPS-Untersuchungen zu nicht-dispergierenden Zust{\"a}nden, die die Bandstrukturen der CuInS2-Schichten {\"u}berlagerten. Bei k-senkrecht-Messungen zeigte sich ein Zustand, dessen Dispersion stark von Berechnungen Eyerts abweicht. Sein Ursprung konnte nicht eindeutig abgeleitet werden konnte, da der Beobachtungsraum aufgrund von Endzustandseffekten und Satellitenst{\"o}rungen stark eingeschr{\"a}nkt war. Generell zeigt ein Vergleich der Berechnungen nach Eyert bzw. Zunger mit entsprechenden Messungen, dass beide Modellrechnungen zu Bindungsenergien f{\"u}hren, die gegen{\"u}ber den Messwerten zu niedrig sind. Die energetische Ausdehnung der charakteristischen Bereiche und deren Lage zueinander wird jedoch zutreffend beschrieben. Konsistent mit Beobachtungen in anderen Arbeiten an analogen Systemen erweist sich dabei die theoretische Behandlung der d-Zust{\"a}nde bei der Modellierung als kritisch. Die Bandl{\"u}cke zwischen d-Charakter-dominierten und p-Charakter-dominierten Bereich wird von Eyert {\"u}bersch{\"a}tzt, von Zunger dagegen untersch{\"a}tzt. Dies l{\"a}sst sich auf die verwendeten N{\"a}herungen (LDA (Zunger), GGA (Eyert)) des Austauschkorrelationspotentials zur{\"u}ckf{\"u}hren. Bei einer Anpassung der von Eyert berechneten Bandstrukturen durch einen geeigneten Energieoffset zeigten sich im Vergleich mit k-parallel-Messungen im Allgemeinen gute, nahezu perfekte {\"U}bereinstimmungen von beobachteten Dispersionsverl{\"a}ufen. Es konnten die effektiven Massen der L{\"o}cher f{\"u}r die k-parallel-Messungen bestimmt werden. Die Werte liegen in der Gr{\"o}ßenordnung des Literaturwertes, jedoch im Mittel bei doppelt so hohen Werten. Ein signifikanter, richtungsabh{\"a}ngiger Trend l{\"a}sst sich aufgrund der starken Streuung nicht feststellen. Im Rahmen der vorliegenden Arbeit konnte ausserdem gezeigt werden, dass die Verwendung eines (111)-Substrates zu einer Dom{\"a}nenbildung aufwachsender CuInS2(112)-Schichten f{\"u}hrt. ARUPS-Messungen an derartigen Schichten bestehen daher aus einer {\"U}berlagerung von Bandstrukturen entlang unterschiedlicher Richtungen. F{\"u}r zuk{\"u}nftige Arbeiten bietet es sich daher an, die (111)-substratinduzierte Fehlorientierung von (112)-Schichten durch ein Step-Flow-Wachstum auf Substraten mit Miscut zu unterbinden.}, subject = {Photovoltaik; D{\"u}nnschichtsolarzelle; Bandstruktur; Chalkopyrit; ARUPS; CIS; DFT; Band structure; Chalcopyrite; ARUPS; CIS; DFT}, language = {de} } @phdthesis{Sohal2006, author = {Sohal, Rakesh}, title = {CVD growth of (001) and (111) 3C-SiC epilayers and their interface reactivity with praseodymium oxide dielectric layers}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-121}, school = {BTU Cottbus - Senftenberg}, year = {2006}, abstract = {In this work, growth and characterisation of 3C-SiC thin films, investigation of oxidation of thus prepared layers and Pr-silicate and AlON based interface with SiC have been studied. Chemical vapor deposition of 3C-SiC thin films on Si(001) and Si(111) substrates has been investigated. Prior to the actual SiC growth, preparation of initial buffer layers of SiC was done. Using such a buffer layer, epitaxial growth of 3C-SiC has been achieved on Si(111) and Si(001) substrates. The temperature of 1100°C and 1150°C has been determined to be the optimal temperature for 3C-SiC growth on Si (111) and Si(001) substrates respectively. The oxidation studies on SiC revealed that a slow oxidation process at moderate temperatures in steps was useful in reducing and suppressing the g-C at the SiO2/SiC interface. Clean, graphitefree SiO2 has been successfully grown on 3C-SiC by silicon evaporation and UHV anneal. For the application of high-k Pr2O3 on silicon carbide, plausible interlayer, Pr-Silicate and AlON, have been investigated. Praseodymium silicate has been prepared successfully completely consuming the SiO2 and simultaneously suppressing the graphitic carbon formation. A comparatively more stable interlayer using AlON has been achieved. This interlayer mainly consists of stable phases of AlN along with some amount of Pr-aluminates and CN. Such layers act as a reaction barrier between Pr2O3 and SiC, and simultaneously provide higher band offsets.}, subject = {Siliciumcarbid; Kristallfl{\"a}che; Dielektrische Schicht; CVD-Verfahren; Oxidation; Oxidation}, language = {en} } @phdthesis{KlocekJolanta2011, author = {Klocek Jolanta,}, title = {Processing and investigation of thin films with incorporated carbon species for possible application as low-k materials}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-24358}, school = {BTU Cottbus - Senftenberg}, year = {2011}, abstract = {In this thesis the detailed investigations concerning processing and stability of thin films including carbon species and their possible application as materials of a low dielectric constant (low k) are presented. In order to gather a complex information regarding the chemical, morphological and dielectric properties of the produced layer a combination of the spectroscopy: X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and Fourier transform infrared spectroscopy (FTIR), microscopy: atomic force microscopy (AFM) and electrical characterization: capacitance-voltage technique (CV) have been applied. The films deposited by means of variety of techniques have been described, ranging from evaporation, through spraying and dropping to spin-coating. Regarding the possible low-k application, a considerable attention has been paid to the hybrid organic-inorganic 3-aminopropyl-trimethoxysilane (APTMS) based composite materials enriched with carbon species coming from the following dopants: C60 fullerenes, [6,6]-phenyl-C61-butyric acid (PCBM), copper phthalocyanine (CuPc), and tris(dimethylvinylsilyloxy)-POSS (POSS). In the following thesis progressive steps leading to gradual decreasing of the resulting permittivity of the hybrid material is presented. As revealed by the performed investigations, the replacement of C60 within the APTMS based matrix by its better soluble derivative PCBM allows the increase of the concentration of the carbon species within the composite films. The introduction of POSS as an additional dopant gave the opportunity of increasing the resistance of the produced material against the ambient influence. With the excess of the POSS concentration an original fractal-shaped cluster formation has been observed. Finally, the dispersion of the properly chosen low concentration of CuPc and POSS molecules within the APTMS based matrix led to the fabrication of homogenous layer with an ultra-low dielectric constant of 1.8.}, subject = {R{\"o}ntgen-Photoelektronenspektroskopie; Rasterkraftmikroskopie; R{\"o}ntgen-Photoelektronenspektroskopie; Kapazit{\"a}t-Spannungs-Charakteristik; 3-Aminopropyltrimethoxysilan; Low-k-Materialien; Rasterkraftmikroskopie; X-ray photoelectron spectroscopy; Capacitance-voltage characterization; 3-Aminopropyltrimethoxysilane; Low-k materials; Atomic force microscopy}, language = {en} } @phdthesis{Hartmann2018, author = {Hartmann, Claudia}, title = {Surface and interface characterization of CH₃NH₃PbI₍₃₋ₓ₎Clₓ and CsSnBr₃ perovskite based thin-film solar cell structures}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-46358}, school = {BTU Cottbus - Senftenberg}, year = {2018}, abstract = {The chemical and electronic structure of hybrid organometallic (CH₃NH₃PbI₍₃₋ₓ₎Clₓ) and inorganic (CsSnBr₃) perovskite materials on compact TiO₂ (c-TiO₂) is studied using x-ray and electron based spectroscopic techniques. The morphology and local elemental composition of CH₃NH₃PbI₍₃₋ₓ₎Clₓ, used as absorbers in PV devices, defining the film quality and influencing the performance of respective solar cells is studied in detail by using photoemission electron microscopy (PEEM). An incomplete coverage, with holes reaching down to the c-TiO₂ was revealed; three different topological regions with different degrees of coverage and chemical composition were identified. Depending on the degree of coverage a variation in I oxidation and the formation of Pb⁰ in the vicinity of the c-TiO₂ is found. The valence band maxima (VBM) derived from experimental data for the perovskite and c-TiO₂, combined with information from literature on spiro-MeOTAD suggests an energy level alignment resulting in an excellent charge selectivity at the absorber/spiro-MeOTAD and absorber/c-TiO₂ interfaces respectively. Further, the derived energy level alignment indicates a large recombination barrier (~2 eV), preventing shunts due to direct contact between c-TiO₂ and spiro-MeOTAD in the pin-holes. In-situ ambient pressure hard x-ray photoelectron spectroscopy (AP-HAXPES) studies of 60 and 300 nm CH₃NH₃PbI₍₃₋ₓ₎Clₓ have been performed under varies conditions (i.e. vacuum/water and dark/UV light) to gain insight into the degradation mechanism responsible for the short lifetime of the absorber. The 60 nm perovskite forms Pb⁰ in water vapor (non-defined illumination) in presence of x-rays. The 300 nm perovskite sample shows a complex behavior under illumination/dark. In water vapor/dark the perovskite dissolves into its organic (MAI) and inorganic (PbI₂) components. Under illumination PbI₂ further decomposes to Pb⁰ induced by UV light and x-rays. For alternative inorganic CsSnBr₃ perovskites, the impact of SnF₂ on the chemical and electronic structure is studied to identify its role for the improved performance of the solar cell. HAXPES and lab-XPS measurements performed on CsSnBr₃ with and without SnF₂ indicate two Sn, Cs, and Br species in all samples, where the second Sn species is attributed to oxidized Sn (Sn⁴⁺). When adding SnF₂ to the precursor solution, the coverage is improved and less Sn⁴⁺ and Cs and Br secondary species can be observed, revealing an oxidation inhibiting effect of SnF₂. Additionally, SnF₂ impacts the electronic structure, enhancing the density of states close to the VBM.}, subject = {Perovskite; Photoelectron spectroscopy; Thin-film solar cell; Solid-state physics; Photovoltaics; Photovoltaik; Festk{\"o}rperphysik; D{\"u}nnschichtsolarzelle; Photoelektronenspektroskopie; Perowskite; Fotovoltaik; Halbleiter; D{\"u}nnschichtsolarzelle; Perowskit; Photoelektronenspektroskopie}, language = {en} } @phdthesis{Mandal2008, author = {Mandal, Dipankar}, title = {Ultra-thin films of a ferroelectric copolymer: P(VDF-TrFE)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-5628}, school = {BTU Cottbus - Senftenberg}, year = {2008}, abstract = {Spin-cast films of the ferroelectric copolymer P(VDF-TrFE) are attractive for various applications. For such films the question arises whether there exists a depending on film thickness of ferroelectric functionality. In this work, ultra-thin films of P(VDF-TrFE) up to 0.35nm of thickness have been successfully spin coated, which is quite promising in respect of low cost approach in the electronic industry. This thesis focuses on the preparation of the ultra-thin P(VDF-TrFE) copolymer film and its characterizations to find out a scientific guideline for the suitable application as a non-volatile memory element. Therefore, the ultra-thin film preparations have been investigated initially. Optimization of annealing parameters has been done to get the ferroelectric beta phase and thickness determination is also done carefully. The copolymer layer thickness could be determined down to about 0.35 nm. Photoelectron spectroscopy is used extensively for the characterization of the thin film. Eventually, longer time X-ray irradiation of the P(VDF-TrFE) sample may cause a phase change from ferroelectric to paraelectric. Therefore the X-ray irradiation time was also optimized. With photoelectron spectroscopy, the interface chemistry of the P(VDF-TrFE) copolymer and different electrode materials was studied. The interfaces aluminum/P(VDF-TrFE) and PEDOT:PSS/P(VDF-TrFE) are compared. PEDOT:PSS is a conducting polymer, Poly(3,4-ethylenedioxidethiophene): poly(styrenesulfonate). This data suggested that an interface layer is formed for electrodes, made of aluminum. An interface reaction occurs in both cases: for aluminum as top and as bottom electrode. In contract, the organic PEDOT:PSS electrode shows no chemical interaction with the P(VDF-TrFE) copolymer. The much lower reactivity of organic electrode, compare to aluminum, gives a direct hint to improved functional properties of thin organic ferroelectric films. In terms of a low cost approach for electronics, based on organic devices, the introduction of organic non volatile memories is of great importance. P(VDF-TrFE) copolymer is the material with a very hopeful perspective. In next part electrical measurements with P(VDF-TrFE) have been done. By capacitance voltage measurements, the ferroelectric behavior of the polymer by measurements at elevated temperatures (Curie-Point) is confirmed, a threshold for remanent poalrization for films below 100 nm is found, if aluminum electrodes are used, but with inert electrodes, a downscaling of a low coercitive field was possible down to ten nm. This is very important, because due to the high coercitive field of the copolymer (>50 MV/m), ultrathin films for low operation voltages are needed. A prerequisite for memory applications is a high retention time, this was also confirmed. By the help of Near edge X-ray Absorption Spectroscopy (NEXAFS) the possible ferroelectric dipole orientation have been also investigated. The average dipole orientation (perpendicular to the substrate) is observed up to 0.35 nm P(VDF-TrFE) copolymer films when PEDOT:PSS/Si substrate is used. The ferroelectric properties of ultrathin films down to a layer thickness of 10nm were characterized using spectroscopic (F1s NEXAFS) and electrical methods (Capacitance voltage). The results indicates an extrinsic switching mechanism with a much lower opera-tion voltage than for a collective intrinsic switching. Both independent methods agree that there is no critical thickness for spincoated copolymer films down to 10 nm, if an adapted system of electrodes is used.}, subject = {Grenzfl{\"a}chenchemie; Photoelektronenspektroskopie; Polymerfilm; Ultrad{\"u}nne Filme; Dipolorientierung; Nichtfl{\"u}chtige Speicher; P(VDF/TrFE) Copolymer; Ultra-thin film; Dipole orientation; Non volatile memory application; P(VDF/TrFE) copolymer}, language = {en} } @phdthesis{Schweizer2004, author = {Schweizer, Stefan}, title = {Dynamisches Verhalten von Silizium-Elektroden in Fluor-haltigen Elektrolyten}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-000000526}, school = {BTU Cottbus - Senftenberg}, year = {2004}, abstract = {Einige Effekte von Silizium sind bis heute ungekl{\"a}rt. Dazu z{\"a}hlt Oxidation von hoch-dotiertem n-Si in Fluor-haltigen S{\"a}uren im Dunkeln. Diese Oxidation wurde erstmals systematisch untersucht und zur Grundlage eines Modells f{\"u}r Elektroneninjektion gemacht. Die angenommenen Oberfl{\"a}chenkomplexen erkl{\"a}ren den Einsatz der Kennlinien. Weitere Untersuchungen zur Identifizierung des Komplexes sowie seiner energetischen Position bieten sich an. Mit zyklischen Voltammogrammen wurde gezeigt, dass die Vorschubgeschwindigkeit des Potentials entscheidend f{\"u}r die Gestalt der Kennlinien ist. Schon 20mV/s ist f{\"u}r das untersuchte System zu schnell, um einen Gleichgewichtszustand zu erreichen. Dies wird durch die Ausbildung von Hysteresen klar erkennbar. Der initielle Strompuls zeigt eine vielfache Stromdichte gegen{\"u}ber den bekannten Werten der nachfolgenden Oszillationspulse. Die Wasserstoff-terminierte Grenzfl{\"a}che wird innerhalb weniger Zehntelsekunden oxidiert und passiviert. Alle nachfolgenden Strompulse k{\"o}nnen als weniger gut synchronisierte Oxidationen verstanden werden.}, subject = {Silicium; Elektrochemische Oxidation; Cyclovoltammetrie; Silizium; Oxidation; Voltammogramm; Injektion ; AFM}, language = {de} } @phdthesis{Goryachko2002, author = {Goryachko, Andriy}, title = {Investigations of perspective materials for aggressively scaled gate stacks and contact structures of MOS devices}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-000000342}, school = {BTU Cottbus - Senftenberg}, year = {2002}, abstract = {The thesis discusses a fundamental question of reconstruction on the Si(100) surface as well as three material combinations, which are important for perspective microelectronics technologies: Si/Pr2O3/Si(100), W/WNx/poly-Si/SiO2/Si(100), and CoSix/Si(100). A refined mixed ad-dimer model is developed for the Si(100)-c(4´4) reconstruction on the basis of scanning tunnelling microscopy investigations. A thermal stability of Pr2O3/Si(100) and Si/Pr2O3/Si(100) structures is studied with ion sputtering assisted Auger electron spectroscopy. The latter technique is also applied for precise determination of O and N content in the new W/WNx/poly-Si/SiO2/Si(100) structure, and to study the preferential sputtering of Si in CoSi2, CoSi, and Co2Si phases on Si(100) surface. The WSix/poly-Si/SiO2/Si(100) system, which was previously used in microelectronics, is studied for comparison. The preferential sputtering of Si in WSix is shown to be qualitatively similar as in the CoSix case.}, subject = {Silicium; Kristallfl{\"a}che; Praseodymoxide; MOS Wolframnitride; D{\"u}nne Schicht; Silicon; Praseodymium oxide; Tungsten nitride; Tungsten silicide; Cobalt silicide}, language = {en} } @phdthesis{Schulz2001, author = {Schulz, Detlev}, title = {Wachstumsph{\"a}nomene und Stickstoffdotierung bei der Sublimationsz{\"u}chtung von 6H-Siliciumcarbid}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-000000044}, school = {BTU Cottbus - Senftenberg}, year = {2001}, abstract = {Die Keimoberfl{\"a}che ist durch das Vorhandensein einer St{\"o}rschicht charakterisiert, die durch die mechanische Kristallbearbeitung hervorgerufen wird. Diese Schicht kann die Ursache f{\"u}r zus{\"a}tzliche Defekte sein. Die Untersuchungen der Oberfl{\"a}chenmorphologie zeigen, daß ein {\"U}berschuß an Silicium im Quellmaterial notwendig ist, um ein defektfreies Wachstum in den ersten Stadien zu erm{\"o}glichen. Sowohl ein Oxidationsschritt vor dem Wachstum als auch die Anwendung von fehlorientierten Keimen f{\"u}hrten nicht zum gew{\"u}nschten Stufenfluß. Im Konzentrationsbereich von 1x10^18 <= c_N (cm^-3) <= 3x10^19 wurden 6H-SiC-Einkristalle gez{\"u}chtet, sowohl auf (0001)- als auch (000-1)-Keimen. Der Einbau von Stickstoff bewirkt das Absinken der Wachstumsgeschwindigkeit, was mit dem ''site-competition''-Modell erkl{\"a}rt werden kann. Die S{\"a}ttigung der Stickstoffkonzentration im Kristall in Abh{\"a}ngigkeit vom N_2/Ar-Verh{\"a}ltnis konnte durch eine Langmuir-Isotherme beschrieben werden. Die Polarit{\"a}t der Keimoberfl{\"a}che beeinflußt den Stickstoffeinbau. Die Stickstoffkonzentration im gewachsenen Kristall ist auf der C-terminierten Fl{\"a}che ca. doppelt so hoch wie auf der Si-terminierten. Es wurde gezeigt, daß die Oberfl{\"a}chenmorphologie zus{\"a}tzlich zur Keimpolarit{\"a}t den Stickstoffeinbau beeinflußt.}, subject = {Siliciumcarbid; Polytypie; Kristallz{\"u}chtung; Stickstoff; Dotierung; Siliciumcarbid; 6H-Polytyp; Einkristallz{\"u}chtung; Stickstoffeinbau; Oberfl{\"a}chenmorphologie}, language = {de} } @phdthesis{Das2015, author = {Das, Chittaranjan}, title = {Spectroscopic and electrochemical study of TiO₂/Si photocathode}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-36924}, school = {BTU Cottbus - Senftenberg}, year = {2015}, abstract = {Diese Dissertationsschrift besch{\"a}ftigt sich mit der Atomlagenabscheidung (ALD) d{\"u}nner TiO₂-Schichten auf p-Typ Silizium, untersucht die elektronischen Eigenschaften der abgeschiedenen Schichten und beschreibt die elektrochemische Charakterisierung von TiO₂/Si-Photoelektroden. Die Abscheidungsparameter, die elektronischen Eigenschaften und die Stabilit{\"a}t der TiO₂/Si-Proben werden miteinander korreliert. Mittels der ALD-Technik wurden TiO₂-Schichten mit zwei verschiedenen Prekursoren (Titan- Isopropoxid und Titan-Methoxid) auf Si-Substraten abgeschieden. Labor- und Synchrotron basierte R{\"o}ntgen-Spektroskopietechniken wurden benutzt, um die abgeschiedenen Schichten zu charakterisieren. Die Qualit{\"a}t der Schichten wurde dabei mittels R{\"o}ntgen-Photoelektronenspektroskopie (XPS) beurteilt, wobei die St{\"o}chiometrie, das Ti³⁺/Ti⁴⁺-Verh{\"a}ltnis sowie Defektzust{\"a}nde in den TiO₂-Filmen Kriterien darstellten. Um verschiedene Polymorphe von TiO₂ zu erhalten, wurde die Heizmethode der Schichten innerhalb der ALD-Prozedur variiert. Die elektronischen Eigenschaften amorpher und Anatas-TiO₂-Schichten wurden mittels Synchrotronstrahlung bestimmt und mit denen eines TiO₂-Rutil-Einkristalls verglichen. R{\"o}ntgen- Absorptionsspektroskopie (XAS) und resonante Photoelektronenspektroskopie (res-PES) wurden mit Synchrotronstrahlung durchgef{\"u}hrt. Dabei diente die XAS der Bestimmung der Art des Polymorphen und der elektronischen Struktur der TiO₂-Schichten. Res-PES-Messungen wurden an den O1s- und Ti2p- Kanten durchgef{\"u}hrt, um Auger-Prozesse mit multiplen Loch-Endzust{\"a}nden sowie polaronische und Ladungstransferzust{\"a}nde zu untersuchen und um die elektronische Bandl{\"u}cke der TiO₂-Schichten zu bestimmen. Eines der Hauptergebnisse dieser Arbeit stellt die Bestimmung der partiellen Zustandsdichten (pDOS) von Sauerstoff und Titan im Valenz- und Leitungsband dar. In der Analyse der res-PES-Daten wurde die pDOS mit den entsprechenden Bandkantenpositionen kombiniert, um die energetische Lage der Ladungsneutralit{\"a}tsniveaus (‚Charge neutrality levels') der verschiedenen TiO₂-Polymorphe zu ermitteln. Photoelektrochemische Messungen wurden an unbeschichteten und TiO₂-beschichteten Si- Photoelektroden durchgef{\"u}hrt. Dabei wurde die elektrochemische Performance der Photoelektroden in verschiedenen Elektrolytmedien mit pH-Werten zwischen 1 und 13 untersucht. Die Beschichtung der Si- Oberfl{\"a}che mit einer d{\"u}nnen TiO₂-Schicht verbesserte die Performance der Si-Photoelektrode, wobei die Stabilit{\"a}t der Elektrode in allen untersuchten Elektrolytmedien w{\"a}hrend der gesamten Messdauer von 12 Stunden erh{\"o}ht wurde. Außerdem wurde festgestellt, dass die TiO₂/Si-Photoelektrode weniger empfindlich auf {\"A}nderungen des pH-Wertes reagiert. Die elektrochemischen Ergebnisse werden auf Basis der elektronischen Eigenschaften der TiO₂-Schichten diskutiert. Die durch die spektroskopischen Messungen bestimmte elektronische Bandl{\"u}cke sowie die photoelektrochemischen Charakterisierungen werden zur Erkl{\"a}rung der Performance und Stabilit{\"a}t der TiO₂/Si-Photoelektroden herangezogen. Die Arbeit adressiert außerdem die Stabilit{\"a}t von mikrostrukturierten Photoelektroden (SiMP), die elektrochemisch pr{\"a}pariert wurden. Zun{\"a}chst verschlechterte sich die Stabilit{\"a}t der SiMP schneller als bei der planaren Si-Photoelektrode. Jedoch f{\"u}hrte die Nutzung einer TiO₂-ALD-Schutzschicht auf der SiMP zu einer besseren Gesamtperformance der SiMP auch im Vergleich zum System TiO₂/ planares Si.}, subject = {ALD; TiO2; Photocathodes; XPS; XAS; Atomlagenabscheidung; Photokathode; R{\"o}ntgenphotoelektronenspektroskopie; R{\"o}ntgenabsorptionsspektroskopie; Atomlagenabscheidung; Photokathode; R{\"o}ntgenabsorptionsspektroskopie; R{\"o}ntgen-Photoelektronenspektroskopie}, language = {en} } @phdthesis{Kutukova2023, author = {Kutukova, Kristina}, title = {In-situ study of crack propagation in patterned structures of microchips using X-ray microscopy}, doi = {10.26127/BTUOpen-6256}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-62567}, school = {BTU Cottbus - Senftenberg}, year = {2023}, abstract = {The motivation of this thesis was to control crack steering into regions of engineered 3D-nanopatterned structures with high fracture toughness and to determine the local critical energy release rate for crack propagation in 3D-nanopatterned systems. On-chip copper interconnect structures of advanced microchips, insulated by organosilicate glasses, were chosen as an example system to study fracture on small scale, since this is a well-defined 3D- nanopatterned system and since a high mechanical robustness is requested for microchips. An experiment for in-situ high-resolution 3D imaging of the fracture behavior of 3D-nanopatterned structures and of the kinetics of microcrack propagation in solids was designed and applied, combining a miniaturized micromechanical test and high-resolution X-ray imaging. Particularly, a miniaturized piezo-driven double cantilever beam test set-up (micro- DCB) was integrated in a laboratory X-ray microscope, and nano X-ray computed tomography was applied for high-resolution 3D imaging of the microcrack evolution in the on-chip interconnect stack of microchips manufactured in the 14 nm technology node. The measured geometry of the microcrack at several loading steps during the micro-DCB test and the subsequent data analysis based on linear elastic fracture mechanics and the Euler-Bernoulli beam model were the basis for the development and application of a new methodology to determine the critical energy release rate for crack propagation in sub- 100 nm regions of a processed wafer quantitatively. It was experimentally proven that specially designed metallic guard ring structures at the rim of the microchips dissipate energy in such a way that the microcrack propagation is efficiently slowed down and eventually stopped, i.e. they are effective to prevent mechanical damage of microchips. It was demonstrated that it is possible to steer the microcrack in a controlled way by tuning the fracture mode mixity locally at the crack tip. The established concept for a controlled crack propagation provides the basis for further fundamental studies of the fracture behavior of nanoscale materials and structures. The results have significant effects for the understanding of fracture mechanics at small scales, e.g. in microchips, but also in other nanopatterned materials, e.g. in bio-inspired, hierarchically structured engineered materials. The experimental results gathered at realistic microelectronic products provide valuable information to control the crack path in on-chip interconnect stacks for design-for-reliability in semiconductor industry and to manufacture mechanically robust microchips in leading-edge technology nodes. The experimental study of controlled microcrack steering into regions with high fracture toughness provides knowledge for the design of guard ring structures in microchips to stop the propagation of microcracks, e.g. generated during the wafer dicing process.}, subject = {R{\"o}ntgenmikroskopie; In-situ-Rissausbreitung; On-Chip-Interconnect-Stacks; Bruchmechanik; Schutzringstrukturen; X-ray microscopy; In-situ crack propagation; On-chip interconnect stacks; Fracture mechanics; Guard ring structures; Rissausbreitung; Mikroriss; Bruchverhalten; Bruchmechanik; Nanostrukturiertes Material; Chip; R{\"o}ntgenmikroskopie}, language = {en} } @phdthesis{Mueller2010, author = {M{\"u}ller, Sebastian}, title = {Synchrotron radiation spectroscopy studies of the initial interaction of Chromium and Cobalt with the surface of Titanium Dioxide}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-18914}, school = {BTU Cottbus - Senftenberg}, year = {2010}, abstract = {In the framework of this thesis, synchrotron radiation based spectroscopy methods are applied to study the electronic structures of stoichiometric Rutile single crystals and TiO2 thin films, and the initial stage of chromium and cobalt growth on TiO2 thin films. Resonance photoemission spectroscopy of clean TiO2 at the Ti L2,3 edges led to Auger-like features, with kinetic energies corresponding to the Ti L2,3M4,5M4,5 Auger decay channels. The presence of these features is assigned to origin from a d2L2 charge transfer state. The resonance of the Ti L3M2,3V Auger channel at the Ti L2 edge is assigned to the L2L3V Coster-Kronig Auger, followed by the normal L3M2,3V Auger decay. The deposition of chromium on the TiO2 film causes a strong interaction at the interface, in which TiO(2-x) is formed together with chromium in the Cr 3+ state. Besides the oxidized component, contribution of metallic chromium is found as well. In the ultra-low coverage regime, post-deposition oxidation is observed, in which metallic chromium is oxidized to Cr2O3, accompanied by re-oxidation of the substrate to TiO2. The interface reaction is also reflected by the appearance of two defect states in the band gap. Resonant photo-emission at the Cr 2p and Ti 2p edges shows well distinguishable Cr 3d respectively Ti 3d character of the respective states. Indications for self-cleaning properties are found by removal of surface carbon during storage in UHV, but the influence of chromium on these properties is not studied in detail. The interaction between cobalt and TiO2 is weaker than that of chromium and TiO2. Nevertheless, an interface reaction is found, in which some of the deposited cobalt is oxidized, while the oxide support is partly reduced. The particular oxidation state of Cobalt is identified by means of multiplet calculation including charge transfer and crystal field effects. The calculated XAS and XPS spectra indicate Co 2+ in a tetrahedral coordination with four oxygen atoms. The metallic component of cobalt gives rise to a broad resonance in the valence band down to -20 eV, with a pronounced satellite feature that reflects the oxidized component.}, subject = {Spektroskopie; Titandioxid; Atomare Multiplett-Rechnung; Resonante Photoemission; Metall-Metalloxid-Wechselwirkung; Titanium dioxide; Metal/metal-oxide interaction; Multiplet-calculation; Resonant photoemission}, language = {en} } @phdthesis{Gerlich2012, author = {Gerlich, Lukas}, title = {In situ ARXPS Charakterisierung von tantalbasierten Barriereschichten}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-28485}, school = {BTU Cottbus - Senftenberg}, year = {2012}, abstract = {Als eine Folge der Miniaturisierung aller integrierten elektrischen Bauteile wird der spezifische Widerstand der TaN/Ta Doppelsperrschichten ein zunehmend wichtiger Parameter f{\"u}r die Schaltgeschwindigkeit beim 32 nm Technologieknoten. In Rahmen dieser Arbeit wird die Optimierung der Abscheidung von TaN/Ta Stapeln durchgef{\"u}hrt, mit dem Ziel die Tantalnitridschichtdicke zu minimieren und das Tantal in der leitf{\"a}higeren alpha-Phase wachsen zu lassen. Im ersten Teil der Studie wurde in situ ARXPS verwendet, um das Wachstum von verschiedenen Tantalnitridschichten auf SiO2 und SiCOH in Abh{\"a}ngigkeit der Abscheidezeit, des Stickstoffflusses und der Abscheideleistung zu untersuchen. Im zweiten Teil wurde die kristalline Phase 20 nm dicken Tantal Schichten abgeschieden auf verschiedenen Tantalnitridschichten, die in der Wachstumsstudie vorgestellt worden sind, untersucht. Die wichtigsten Erkenntnisse sind das Auftreten von Tantalkarbid und Tantalsilizid als Zwischenschichtverbindungen bei der Abscheidung auf SiCOH und nur Tantalsilizid f{\"u}r die Abscheidung auf SiO2. Demzufolge w{\"a}chst alpha-Tantal vorzugsweise auf Tantalkarbid und stickstoffreichen Zwischenschichten, w{\"a}hrend Silizid an der Schnittstelle das Wachstum von beta-Tantal f{\"o}rdert. Um die Ergebnisse zu {\"u}berpr{\"u}fen, wurden zwei weitere Modifikationen des Interfaces untersucht. So wurde eine kleinere Bias-Leistung f{\"u}r eine Abscheidung von Tantalnitrid auf SiO2 benutzt, um die Rolle des Tantalsilizids zu best{\"a}tigen. Außerdem wurde eine thermische Behandlung einer d{\"u}nnen Tantalschicht auf SiCOH durchgef{\"u}hrt, um die Rolle des Tantalkarbids zu best{\"a}tigen. Schließlich ergab die Kontaktwiderstandsmessung in Viaketten auf strukturierten Wafern f{\"u}r vier ausgew{\"a}hlte Prozesse tendenziell den gleichen Verlauf wie die Schichtwiderstandsergebnisse der entsprechenden Barrierenaufbauten der Experimente auf blanken Testwafern.}, subject = {Photoelektronenspektroskopie; Tantal; ARXPS; Barriere; Interface; Tantalum; ARXPS; Barrier; Interface}, language = {de} }