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Dissertation
High-Speed Semiconductor Lasers based on Low-Dimensional Active Materials for Optical Telecommunication
(2012-07-10)
The scope of this work is the fundamental growth, tailoring and characterization of self-organized indium arsenide quantum dots (QDs) and their exploitation as active region for diode lasers emitting in the 1.55 µm range. This wavelength regime is especially interesting for long-haul telecommunications as optical fibers made from silica glass have the lowest optical absorption. Molecular Beam Epitaxy is utilized as fabrication technique for the quantum dots and laser structures. The results presented in this thesis ...
Dissertation
Development of directly modulated high speed telecommunication lasers based on surface defined feedback gratings
(2012-10-31)
High-speed semiconductor lasers are an integral part in the implemen- tation of high-bit-rate optical communications systems. They are com- pact, rugged, reliable, long-lived, and relatively inexpensive sources of coherent light. Due to the very low attenuation window that exists in the silica based optical fiber at 1.55 μm and the zero dispersion point at 1.3 μm, they have become the mainstay of optical fiber com- munication systems. For the fabrication of lasers with gratings such as, distributed bragg reflector ...
Dissertation
GaInAsP-basierende Resonatorstrukturen
(2006-10-27)
Physikalische Grundlagenforschung und anwendungsorientierte physikalische Forschung auf den Gebieten nanoskaliger kristalliner und amorpher fester Körper haben in vielfacher Weise eine große Bedeutung. Neben dem Verständnis für die Struktur der Materie und die Wechselwirkung von Objekten von der Größe einiger Atome ist die Erkenntnis über die physikalischen Eigenschaften nanostrukturierter Systeme von hohem Interesse. Diese Forschung eröffnet die Möglichkeit, die mit der Mikroelektronik begonnene Miniaturisierung ...
Dissertation
Herstellung von spannungsoptimierten Silizium-Membranen durch den elektrochemischen Ätzstopp an pn-Übergängen
(2004-12-15)
Vielen Sensoren in mikroelektromechanische Systemen (MEMS) liegen Siliziummembranen zu Grunde. Die Membranen werden mit unterschiedlichen Verfahren hergestellt. Zum Teil kann man Opferschichten benutzen. Will man jedoch Membranen aus kristallinem Silizium, so muß man auf Ätzstopptechniken zurückgreifen. Eine gängige Methode verwendet vergrabene p^(+)-Schichten. Die sehr hohe Dotierung des Siliziums führt jedoch zu unüberwindbaren Problemen bei der Schaltkreisintegration. Die Verwendung von pn-Übergängen beim ...
Dissertation
Spontane Strukturbildung in Mehrschichtsystemen unter Verwendung Molekularer Gläser
(2005-03-03)
Den Schwerpunkt dieser Dissertation bildet zum einen die Entwicklung eines theoretischen Modells zur Beschreibung des Strukturbildungsprozesses in organisch/anorganischen Doppelschichtsystemen und zum anderen die Untersuchung der Übertragbarkeit dieser theoretisch gewonnenen Ergebnisse auf reale Systeme. Hierzu dienen systematische experimentelle Untersuchungen dieses Phänomens an einem Testsystem. Der Bereich der selbstorganisierenden Systeme ist von hohem wissenschaftlichen Interesse, erlaubt er doch die Realisierung ...
Dissertation
Surface modifications of nanocrystalline diamond films and their functionalization with phthalocyanines
(2016-06-30)
Boron-doped diamond is a promising electrode material for a number of applications providing efficient carrier transport, a high stability of the electrolytic performance with time, a possibility for dye-sensitizing with photosensitive molecules, etc. It can be functionalized with electron donor molecules, like phthalocyanines or porphyrins, for the development of light energy conversion systems. For effective attachment of such molecules, the diamond surface has to be modified by plasma- or photo-chemical processes ...
Dissertation
1.55 µm High-Speed QDs Lasers for Optical Telecommunication Applications
(2014-12-19)
In this work investigation of the QDs formation and the fabrication of QD based semiconductor lasers for telecom applications are presented. InAs QDs grown on AlGaInAs lattice matched to InP substrates are used to fabricate lasers operating at 1.55 µm, which is the central wavelength for far distance data transmission. This wavelength is used due to its minimum attenuation in standard glass fibers.
The incorporation of QDs in this material system is more complicated in comparison to InAs QDs in the GaAs system. Due ...
Dissertation
Molecular Beam Epitaxial Growth of III-V Semiconductor Nanostructures on Silicon Substrates
(2013-07-24)
The main focus and concerns of this PhD thesis is the growth of III-V semiconductor nanostructures (Quantum dots (QDs) and quantum dashes) on silicon substrates using molecular beam epitaxy (MBE) technique. The investigation of influence of the major growth parameters on their basic properties (density, geometry, composition, size etc.) and the systematic haracterization of their structural and optical properties are the core of the research work. The monolithic integration of III-V optoelectronic devices with silicon ...
Dissertation
High temperature-stable InGaAs QDs for the monolithic integration in external-cavity surface-emitting lasers
(2021)
Optically pumped vertical external-cavity surface-emitting lasers (VECSELs), also called semiconductor disk lasers (SDLs), benefit from the flexibility and versatility of the semiconductor material. With a simple cavity layout, fundamental transverse mode operation with a circular output beam and high beam quality is possible. They have excellent heat-sink properties and only require inexpensive multimode diode lasers for pumping. The complete VECSEL structure is only a few micrometers thick which leads to a strong ...
Dissertation
Fabrication and Investigation of Diamond Membranes for Photonic Nanostructures
(2023)
Due to its exceptional physical and chemical characteristics, diamond in a form of thin membranes is a particularly promising material for the fabrication of high-quality photonic devices. Especially for envisioned applications in quantum information technologies and communication, diamond gained, as a host material, an ever-increasing scientific interest based on remarkable properties of different color centers in its crystal lattice, e.g. nitrogen-vacancy centers, serving as single-photon emitters. As a high index ...