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In dieser Arbeit werden das Wachstum und die Charakterisierung der Heterostruktur eines FeFET auf der Grundlage von BaSnO3, LaInO3 und (K,Na)NbO3 Schichten untersucht. Für jedes Material wurden die Wachstumsbedingungen bestimmt und im Hinblick auf die strukturellen und elektrischen Eigenschaften optimiert. Epitaktische BaSnO3 Filme, die auf SrTiO3 Substraten gewachsen sind, weisen eine hohe Dichte an Versetzungen auf, die ihre elektrischen Eigenschaften beeinträchtigen. Die Verwendung von NdScO3 Substraten und Einführung einer SrSnO3 Pufferschicht verbesserten die strukturellen und elektrischen Eigenschaften der BaSnO3 Schichten. Dies ermöglichte schließlich Untersuchungen an der LaInO3/BaSnO3 Grenzfläche. Schon eine geringe La-Dotierung der BaSnO3 Schicht von 0,3 % führte zur Bildung eines 2DEG nach der Grenzflächenbildung und damit zum Einschluss von Elektronen an der Grenzfläche. Dies konnte durch C-V, Van-der-Pauw und Hall-Effekt-Messungen eindeutig nachgewiesen werden. Eine deutliche Verbesserung der strukturellen und elektrischen Eigenschaften der BaSnO3 Schichten wurde durch die Verwendung von LaInO3:Ba Substraten erreicht. Diese sind gitterangepasst an BaSnO3, sodass zum ersten Mal vollständig verspannte Schichten ohne Versetzungen gewachsen werden konnten. Strukturelle und elektrische Eigenschaften von (K,Na)NbO3 Schichten wurden auf SrRuO3/DyScO3 und SrTiO3:Nb-Substraten untersucht. Auf diese Weise wurden der Einfluss der Gitterdehnung auf die kritische Schichtdicke und die Prozesse der plastischen Relaxation des Gitters bestimmt. Die elektrische Charakterisierung ergab einen hohen Leckstrom, der durch strukturelle Defekte verursacht wird. Die gesamte FeFET Heterostruktur wurde auf LaInO3:Ba Substraten gewachsen und untersucht. BaSnO3 und LaInO3 Schichten wuchsen kohärent, während (K,Na)NbO3 Schichten eine plastische Gitterrelaxation aufwiesen. Das führte zur Bildung von Strukturdefekten und zu einer Verschlechterung der ferroelektrischen Eigenschaften. / In this thesis, the design, growth and characterisation of the heterostructure of a FeFET based on BaSnO3, LaInO3 and (K,Na)NbO3 thin films are investigated. For each material, the growth conditions were determined and optimised with respect to their structural and electrical properties. Epitaxial BaSnO3 thin films grown on SrTiO3 substrates exhibit a high density of threading dislocations, which degrade their electrical properties. The use of NdScO3 substrates and the introduction of a SrSnO3 buffer layer improved the structural and electrical properties of the BaSnO3 thin films. This finally allowed investigations on the LaInO3/BaSnO3 heterointerface. Even a low La doping of the BaSnO3 layer of 0.3 % led to the formation of a 2DEG after interface formation and thus to the confinement of electrons at the interface. This could be clearly demonstrated by C-V, Van-der-Pauw and Hall effect measurements. A significant improvement of the structural and electrical properties of the BaSnO3 thin films was achieved by using LaInO3:Ba substrates. These are lattice-matched to BaSnO3 so that, for the first time, fully strained thin films could be grown without dislocations. Structural and electrical properties of (K,Na)NbO3 thin films were investigated on SrRuO3/DyScO3 and SrTiO3:Nb substrates. In this way, the influence of lattice strain on the critical film thickness and plastic lattice relaxation were determined. Their electrical characterisation revealed a high leakage current caused by structural defects. Therefore, the entire FeFET heterostructure was grown and investigated on LaInO3:Ba substrates. The BaSnO3 and LaInO3 thin films were grown coherently, while the (K,Na)NbO3 thin films exhibited plastic lattice relaxation. This led to the formation of structural defects and consequently to a deterioration of their ferroelectric properties.

Made available in DSpace on 2015-05-14T13:21:43Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 4670279 bytes, checksum: 8fd1c311257009cec5cc8ce7df6f03a6 (MD5) Previous issue date: 2014-07-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Barium stannate (BaSnO3) and strontium stannate (SrSnO3) are perovskites type oxyde that have cubic (Pm3m) and orthorhombic (Pbnm) structures, respectively. These materials have received much attention due to their interesting physical and chemical characteristics, leading to a variety of technological applications. In this sense, these two materials were combined to each other in order to obtain powders and thin films of a solid solution, Sr1-xBaxSnO3, with (x = 0, 0.25, 0.50. 0.75 e 1). The solid solution in the of powder presented successive phase transitions ranging from orthorhombic and tetragonal structures to a cubic one with increasing of Ba2+ amount in the composition. These transitions were observed by X-ray diffraction and Rietveld refinement, and confirmed by raman vibrational spectroscopy. Moreover, the crystal structures were also characterized by infrared vibrational spectroscopy (FT-IR), scanning electron microscopy (SEM) and, vibrational spectroscopy. The different types of crystalline structures compositions of the solid solution had different percentage values against the photodiscoloration of the azo dye Remazol yellow gold -RNL. The results indicated that the direct mechanism is probably the most suitable for the cubic structure (BaSnO3), while the indirect gift for this orthorhombic structure (SrSnO3). Moreover, the thin films obtained from cubic system (BaSnO3) showed different growth associated with crystal structure of the substrate, the film composition and the deposition method used (deposition method by a pulsed laser ablation - PLD). The films deposited on amorphous silica and R-sapphire (Al2O3-012) showed polycrystalline growth while the films deposited on LAO (LaAlO3-100) showed an epitaxial growth (h00). In addition, morphological and photoluminescent properties also had suffered strong influence of the above parameters. Regarding the photoluminescent properties, these seem to be specifically related to the type of growth of the films, ie films deposited on LAO showed photoluminescent emission in the visible region a unlike the films occur due to deposited on silica and sapphire-R where a structural short-range order in the film / substrate interface has not led to photoluminescent emissions. Regarding the photocatalytic properties, the films obtained by PLD and with richer compositions Ba2+ were the most active in discoloration yellow gold remazol dye, reaching a maximum photocatalytic efficiency with polycrystalline film BaSnO3 deposited on R-sapphire 84.4 %. The polycrystalline films Sr1-xBaxSnO3 deposited on substrates amorphous silica and LAO also showed strong activity in discoloration of the dye, being more efficient than the polycrystalline epitaxial films. Keywords: Barium stannate, strontium stannate, PLD, photocatalysis, photoluminescence, remazol yellow gold, thin films, descoloration. / O estanato de bário (BaSnO3) e o estanato de estrôncio (SrSnO3) são óxidos do tipo perovskita que apresentam estrutura cúbica (mPm3) e ortorrômbica (Pbnm), respectivamente. Estes materiais possuem propriedades químicas bastante interessantes que levam a diversos tipos de aplicações no ramo tecnológico. Portanto, estes dois materiais combinados foram sintetizados tanto na forma de pó quanto de filmes finos com o objetivo de se obter a solução sólida, Sr1-xBaxSnO3, com (x = 0; 0,25; 0,50; 0,75 e 1). A solução sólida na forma de pó apresentou sucessivas transições de fases com o aumento da quantidade do cátion Ba2+ presente no sistema, passando da estrutura ortorrômbica à tetragonal chegando à cúbica. Estas transições foram observadas pelos difratogramas de raios-X e refinamento Rietveld, sendo confirmada por espectroscopia vibracional raman. Ademais, as estruturas cristalinas também foram caracterizadas por espectroscopia vibracional na região do infravermelho (IV), microscopia eletrônica de varredura (MEV) e espectroscopia vibracional de UV-visível. Os diferentes tipos de estruturas cristalinas das composições da solução sólida apresentaram diferentes valores percentuais frente à fotodescoloração do azo-corante remazol amarelo ouro RNL. Os resultados mostraram que o mecanismo direto provavelmente é o mais indicado para a estrutura cúbica do BaSnO3, enquanto que, o indireto está presente para estrutura ortorrômbica do SrSnO3. Os filmes finos obtidos do sistema cúbico (BaSnO3) apresentaram diferentes tipos de crescimentos associados às estruturas cristalinas dos substratos, composição do filme e com o método de deposição utilizado (método de deposição por ablação a laser pulsado PLD). Os filmes depositados sobre sílica amorfa e safira-R (Al2O3-012) apresentaram crescimento policristalino, enquanto os filmes depositados sobre LAO (LaAlO3-100) apresentaram um crescimento epitaxial (h00). Além disto, as características morfológicas e fotoluminescentes também foram influenciadas pelos parâmetros acima citados. Em relação às propriedades fotoluminescentes, estas especificamente parecem estar relacionadas com o tipo de crescimento dos filmes, ou seja, os filmes depositados sobre LAO apresentaram emissão fotoluminescente na região do visível devido ocorrer uma desordem a curto alcance na interface filme/substrato diferentemente dos filmes depositados sobre sílica e safira-R, onde uma ordem estrutural a curto alcance na interface filme/substrato não conduziu a emissões fotoluminescentes. Em relação às propriedades fotocatalíticas, os filmes obtidos por PLD e os filmes com composições mais ricas em Ba2+ foram os mais ativos na descoloração do corante remazol amarelo ouro, chegando a uma eficiência fotocatalítica máxima com o filme policristalino de BaSnO3 depositado sobre safira-R de 84,4 %. Os filmes policristalinos de Sr1-xBaxSnO3 depositados sobre os substratos de sílica amorfa e LAO também mostrou uma forte atividade na fotodescoloração do corante, sendo os filmes policristalinos mais eficientes que os epitaxiais.

Die vorliegende Arbeit beschäftigt sich mit dem Wachstum von BaSnO3/LaInO3 (BSO/LIO) Schichten mittels Plasma-unterstützter Molekularstrahlepitaxie (PAMBE). Für die Realisierung der BSO/LIO Heterostruktur müssen zuvor Wege für ein stabiles Herstellungsverfahren sowohl der BSO als auch der LIO Schichten gefunden werden. Aus diesem Grund beschäftigt sich der erste Teil dieser Arbeit mit den Herausforderungen der Suboxidbildung und Suboxidquellen. Das Wissen um Suboxide ist alt, aber es wurde bisher nicht stark in der Anwendung der Oxid-MBE berücksichtig oder benutzt. Engagierte Studien werden in dieser Arbeit durchgeführt, die zeigen, dass bei Suboxidquellen wie z.B. der Mischung aus SnO2 und Sn sich die Einbaukinetik gegenüber einer elementaren Quelle (z.B. Zinn) vereinfacht. Die in dieser Arbeit herausgearbeitete Effizienz der Mischquellen hat bereits dazu geführt, dass weitere Oxide wie Ga2O3 und SnO mit Hilfe von Suboxid-MBE gewachsen wurden. Im zweiten Teil dieser Arbeit werden die entwickelten Quellen genutzt und die BSO und LIO Wachstumsparameter bestimmt, sowie deren Abhängigkeit im Kontext von thermodynamischen Ellinghamdiagrammen diskutiert. Die Besonderheit beim BSO Wachstum liegt dabei auf der Verwendung einer Mischquelle bestehend aus SnO2 + Sn wodurch SnO Suboxid gebildet wird, welches zum Wachstum beiträgt. Ein zwei-dimensionalen Elektronengas an der Grenzfläche der BSO/LIO Heterostruktur wird realisiert durch gezielte Grenzflächenterminierung mit Hilfe einer Zellverschlusssequenz. Durch die Kontrolle der Grenzflächenterminierung im Monolagenbereich können Ladungsträgerkonzentrationen im Bereich um 3 - 5 × 1013 cm−2 und Beweglichkeiten μ > 100 cm2/Vs zuverlässig und reproduzierbar realisiert werden. / The present work investigates the growth of BaSnO3/LaInO3 (BSO/LIO) heterostructures using plasma-assisted molecular beam epitaxy (PA-MBE). Prior to the realization of the BSO/LIO heterostructure, ways for stable and reliable growth of both BSO and LIO layers have to be developed. Therefore, the first part of this thesis addresses the challenges of suboxide formation and suboxide sources. The knowledge about suboxides is rather old, however, so far it is barely considered or used in oxide MBE. Dedicated studies performed in this thesis show that for suboxide sources such as a mixture of SnO2 and Sn the growth kinetics simplify compared to an elemental source (e.g., Sn). The efficiency of mixed sources, that is worked out in this thesis, already led to the growth of other oxides such as Ga2O3 or SnO using suboxide MBE. In the second part of this thesis growth parameters for BSO and LIO, using the developed sources, are determined and their dependence in the context of thermodynamic Ellingham diagrams is discussed. The growth of BSO is realized by the use of a mixed source consisting of SnO2 + Sn, which forms SnO suboxide that is contributed to the growth. A two-dimensional electron gas at the interface of the BSO/LIO heterostructure is realized by engineering the interface termination using a controlled cell shutter sequence. By controlling the interface termination down to mono layer precision, charge carrier densities in the range of 3 - 5 × 1013 cm−2 and mobilities μ > 100 cm2/Vs can be achieved reliably and reproducibly.