@phdthesis{Schlykow2019, author = {Schlykow, Viktoria Diana}, title = {Selective growth and characterization of GeSn nanostructures on patterned Si wafers}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-48860}, school = {BTU Cottbus - Senftenberg}, year = {2019}, abstract = {Over the past seven decades Si microelectronics have developed rapidly. The success of the growing microelectronic industry is also caused by the expansion of materials in addition to Si. Open challenges are the monolithic integration of group IV devices on Si photonics as well as overcoming the size mismatch between electronic parts in the nm range and photonic parts in the µm scale. In this thesis the future application of GeSn NIs on Si as a photodetector is evaluated. The key element required for high performance optoelectronic devices is the formation of high-quality GeSn nano-islands (NIs), i.e. overcoming growth challenges such as introduction of defects due to lattice and thermal mismatch between GeSn and Si substrate as well as suppression of Sn precipitation caused by the limited solid solubility of Sn in Ge. To achieve high-quality nanostructures, the selective growth of GeSn NIs on Si(001) seeds via molecular beam epitaxy is investigated, exploiting the advantages of nanoheteroepitaxy (NHE), i.e. growth on nano-patterned substrates. The best compromise between selective growth of GeSn on Si nano-pillars at significant higher growth temperature than the eutectic temperature of GeSn and the incorporation of Sn into the Ge lattice was achieved at 600°C. X-ray diffraction studies confirmed the substitutional incorporation of 1.4at.\% Sn into the NIs avoiding considerable Si interdiffusion from the substrate. Transmission electron microscopy images have shown that dislocations and stacking faults caused by plastic relaxation of the GeSn NIs are located near the NIs/substrate interface and thus, dislocation-free GeSn NIs can be formed, due to gliding out of the threading arms triggered by the NHE approach. The high crystal quality of the GeSn NIs, enables the investigation of the bandgap by μ-photoluminescence (PL) analyses, demonstrating the shrinkage of the direct bandgap with increasing Sn content in the quasi-direct semiconductor. All NIs however feature a β-Sn droplet on their nano-facets. To suppress the out-diffusion of Sn and hence increase the Sn concentration of the GeSn alloy, the GeSn NIs were overgrown with a thin Ge cap layer. The Ge cap successfully hinders the formation of Sn segregates on top of the NIs. Capping at 600 °C and 650°C results in an enrichment of Sn at the surface, forming a GeSn crust with 8±0.5at.\% Sn. This wetting layer both enhances the optoelectronic properties of the NI core and exhibits a relatively strong PL emission attributed to direct radiative recombination. Finally, a first demonstration of a GeSn NIs based photodetector was successful, due to the utilization of Al nano-antennas exhibiting an enhanced light coupling into the GeSn NIs at a wavelength of 700nm. The responsible mechanisms is the local plasmonic field enhancement of the incoming light. The manipulation of the resonance wavelength into the telecommunication regime, i.e. >1550nm, have to be investigated in future studies.}, subject = {Group IV; Nanoheteroepitaxy; Photoluminescence; Selective growth; Gruppe IV; Nanoheteroepitaxie; Photolumineszenz; Selektives Wachstum; Germanium; Zinn; Silicium; Heteroepitaxie; Photodetektor}, language = {en} } @phdthesis{MatbaechiEttehad2021, author = {Matbaechi Ettehad, Honeyeh}, title = {Dielectrophoretic manipulation of yeast cells using CMOS integrated microfluidic}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-55315}, school = {BTU Cottbus - Senftenberg}, year = {2021}, abstract = {The rapid detection of infectious diseases is still an unsolved problem since their identification must be carried out either by cultivation or DNA analysis in a laboratory. The development of point-of-care (PoC) is a current development trend that requires further technological impulses to produce reliable and cost-effective systems. By miniaturizing and integrating microfluidic and electronic components, the advantages of electronic methods can be transferred to the field of PoC testing. The combination of complementary metal-oxide-semiconductor (CMOS) technology with microfluidic platforms allowed the development of fully functional sample-to-result LoC setups, which served the portability of the device even out of the laboratory or hospitals. CMOS-based LoC device can control and manage the data from sensors, microfluidics, and actuators. Dielectrophoresis (DEP) is a non-destructive and non-invasive method promising to be used in PoC medical applications. Utilizing MEMS technology and fabrication of microelectrodes allow DEP to be applied in biomedical applications such as cell manipulation and separation with high speed, sensitivity and without any labeling. Cell detection and separation occupy an important place in diagnostics of viral and infectious diseases such as Influenza and COVID-19. Therefore, rapid, sensitive, and automated LoC devices are needed to detect such diseases. Starting from this point of view, manipulating the cells as a way to detect them using DEP was decided as the main objective of the thesis. This work aimed at developing a miniaturized CMOS integrated silicon microfluidic device, in line with a standard CMOS procedure, for characterization and manipulation of live and dead yeast cells using the DEP technique. Understanding the relationship between the microelectrode's geometry and the magnitude of DEP force, the microfluidic devices can be designed to produce the most effective DEP implication on biological samples. In this work, interdigitated electrode arrays (IDEs) were used to manipulate the cells. This microelectrode was primarily used to detect microorganisms in a solution, based on the measurement of the variation of the dielectric constant by the concentration of the microorganisms. Therefore, finite element simulations were performed to optimize this microelectrode and adapt it to our application. Thus, the IDEs were optimized as a function of finger width and spacing between adjacent fingers. One of the most serious matters related to DEP-based microfluidic devices is that the DEP spectra of the targeted cell should precisely be known. Therefore, the DEP spectrum analysis of various cell suspensions with different medium conductivities was studied comprehensively by finite element simulation and experimentally. This study presented an optimized trapping platform for both detection and separation applications in terms of electrode dimension and electrical parameters.}, subject = {Dielectrophoresis (DEP); Yeast cell; Cell manipulation; Interdigitated electrodes (IDEs); CMOS-integrated microfluidic Lab-on-a-chip; Dielektrophorese (DEP); Hefezelle; Zellmanipulation; Interdigitalelektroden (IDEs); CMOS-integriertes mikrofluidisches Lab-on-a-chip; CMOS; Lab on a Chip; Dielektrophorese; Saccharomyces cerevisiae; Mikrofluidik; Biomedizinische Technik}, language = {en} } @phdthesis{Reichmann2022, author = {Reichmann, Felix}, title = {Germanium, Zinn und (Zink-) Galliumoxid f{\"u}r fortschrittliche Mikro- und Optoelektronik : Einblicke in die elektronische Struktur der Oberfl{\"a}che mit Photoemissionstechniken}, doi = {10.26127/BTUOpen-6208}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-62080}, school = {BTU Cottbus - Senftenberg}, year = {2022}, abstract = {Historically, Ge is one of the oldest materials in the semiconductor industry and its (001) surface has been the subject of extensive investigations by photoelectron spectroscopy. I am going to challenge the predominant attribution of a semi-conducting nature of the Ge(001) surface in this thesis. My investigations reveal the presence of a Ge(001) surface state above the Fermi-level, occupied at room temperature. Employing time- and temperature-dependent angle-resolved photoelectron spectroscopy, I will demonstrate that the presence of this surface state is evidence for the conducting nature of the surface at room temperature. Sparked by the remarkable properties of the GeSn-alloy and a trend towards Ge-Sn-related multiquantum well fabrication, I investigate the surface electronic structure of Ge(001) after adsorption and incorporation of Sn. With an in-depth analysis of surface core-level shifts, I will extend the growth model of the Sn wetting layer formation by also detailing structural changes in the subsurface region. At the same time, the modifications of the electronic structure will be detailed, observing the removal of the Ge(001) surface states, the creation of a new, Sn-related surface state and the initial stages of the Schottky barrier formation. β-Ga₂O₃ a transparent semi-conducting oxide that has sparked a lot of interest over the last decade, because it offers an ultra-wide band gap and high break down voltage. However, due to its monoclinic crystal structure, device fabrication is rather challenging and researchers are already looking into alternative materials. One of these candidates is ϵ-Ga₂O₃ and this work presents a combined study by photoelectron spectroscopy and ab initio calculations of its electronic structure. (Hard) X-rays reveal the impact of photoelectron recoil and the absence of a band bending to the surface, while the dispersion of experimentally determined valence states compares favorably with the calculations based on hybrid density-functional theory. Another alternative to β-Ga₂O₃ be ZnGa₂O₄ and I will present an investigation on the electronic structure of its (100) surface. Due to the novelty of ZnGa₂O₄ single-crystals, I am first going to explore the preparation of a clean and well-ordered surface by standard in-situ sputtering and annealing. I will show that already low annealing temperatures induce Zn-deficiency, leading to non-stoichiometric surfaces, further exacerbated by sputtering. By changing the sputtering parameters and the annealing conditions, the preparation of a surface with sufficient quality for subsequent investigations will be demonstrated. The results by photoemission techniques compare favorably with the expectations from theory and allowing the first fundamental insights into the surface electronic structure.}, subject = {Angle-resolved photoemission spectroscopy; X-ray photoelectron spectroscopy; Germanium-tin; Zinc gallium oxide; Surface science; ARPES; Gallium-Zink-Oxid; XPS; Halbleiteroberfl{\"a}che; Bandstruktur; Elektronenstruktur; Germaniumverbindungen; Galliumverbindungen; ARPES; R{\"o}ntgen-Photoelektronenspektroskopie}, language = {en} } @phdthesis{Becker2023, author = {Becker, Lucas}, title = {The Influence of the early relaxation phase on the threading dislocation density in strain relaxed Si₁₋ₓGeₓ buffer layers on Si(001) substrates}, doi = {10.26127/BTUOpen-6743}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-67431}, school = {BTU Cottbus - Senftenberg}, year = {2023}, abstract = {The integration of germanium (Ge) on silicon (Si) for microelectronics applications requires strain-relaxed SiGe buffer layers (SRB) as virtual substrates. However, the presence of threading dislocations in these layers remains a challenge, as they can affect device performance. Existing methods achieve threading dislocation densities (TDD) around 1 x 10⁵ cm⁻², but a further reduction is desired for industrial applications. A SiGe backside deposition technique originally intended to compensate for wafer bowing surprisingly improves the TDD. The underlying physics remained poorly understood until now. In this work it is shown, that the SiGe backside deposition leads to a parasitic SiGe layer at the edge of the wafer. Partial relaxation of this layer generates dislocations, which fundamentally change the relaxation mechanism of subsequently deposited SiGe layers on the front side. These preexisting dislocations glide from the edge to the center of the wafer, preventing the formation of dislocation bundles and pile-ups. As a result, the TDD decreases significantly for layers with low Ge content. Adjusting the growth conditions and dislocation glide kinetics optimizes early relaxation, achieving a TDD reduction to 4x10⁴ cm⁻² for 25\% Ge buffer layers. Additionally, a novel ring deposition technique provides controlled preexisting dislocations at the wafer's edge, offering better control over the dislocation reservoir than uncontrolled parasitic deposition. Although initial results show promising results, further optimization is needed due to localized mechanical damage during processing. In summary, this research provides insights into strained SiGe layer relaxation, dislocation physics, and their impact on the TDD. By understanding these mechanisms, an enhancement of established buffer approach can be achieved and novel strategies for further TDD reduction can be developed.}, subject = {Silicon; Germanium; Epitaxy; Dislocation; Wafer; Silizium; Epitaxie; Versetzungen; Wafer; Wafer; Silicium; Epitaxie; Versetzung }, language = {en} }