Inst. Festkörperphysik

179 Items

Recent Submissions
Well-ordered iron oxide and sulfide thin films

Davis, Earl Matthew (2018)

In this thesis, the growth of iron oxide and iron sulfide thin films has been investigated. These are materials that are abundantly found in the earth's crust and have long been studied by humanity, having a wide range of properties that have seen their use in many applications. Among these applications, iron oxides have played an important role in catalytic processes such as the Haber-Bosch p...

Electronic and vibrational properties of diamondoid derivatives, graphite, and carbon nanotubes

Tyborski, Christoph (2018)

In this work, we present an analysis of vibrational and electronic properties of diamondoids, graphene, multilayer graphene, graphite, and carbon nanotubes. The realized studies are based on optical spectroscopy, such as Raman spectroscopy, photo luminescence, photo luminescence excitation, and absorption spectroscopy, but also on in-depth model calculations. Although the analyzed material syst...

Optical gain and modal loss in AlGaN based deep UV lasers

Martens, Martin Georg Rudolf (2018)

Because of its direct bandgap covering the ultraviolet (UV) spectral region from 360 nm to 200 nm, the AlGaN material system is a promising candidate for the realization of deep UV laser diodes emitting below 300 nm, being an alternative for bulky and energy consuming excimer or frequency multiplied lasers. Possible applications cover e.g. medical detection, gas sensing, material processing, ...

Phonons and excitons in colloidal CdSe/CdS quantum dots with wurtzite and zincblende crystal structure

Biermann, Amelie Laura (2018)

This thesis presents a thorough analysis of the optical and vibrational properties of colloidal II-VI-semiconductor quantum dots, focussing on the effects of crystal structure differences and the interplay within core-shell QDs on the lattice vibrations, temperature dependent lattice parameters the exciton-phonon coupling and the exciton ne structure. Here, spherical CdSe/CdS QDs of di erent s...

Coherent spectroscopy of InGaAs quantum dots

Strauß, Stefan Maximilian (2018)

Excitons in quantum dots represent a remarkably good two-level system with a large optical dipole transition moment. Although most research currently focuses on enhancing their already outstanding properties as single photon emitters they become also increasingly interesting for experimental fundamental research due to their large dipole transition moment. This thesis presents studies which exp...

Entwicklung einer autark operierenden Plug-and-Play-Einzelphotonenemittereinheit

Schlehahn, Alexander (2018)

Durch die stetige Entwicklung von Anwendungsmöglichkeiten der Quantentechnologie steigt auch die Nachfrage nach effizienten und qualitativ hochwertigen Quellen einzelner Photonen, welche den Grundstein vieler dieser praktischen Konzepte bilden. Daher wird im Rahmen dieser Arbeit die Entwicklung einer kältemittelunabhängigen, fasergekoppelten Einzelphotonenemittereinheit, basierend auf InGaAs-Qu...

Polarization multiplexed photonic integrated circuits for 100 Gbit/s and beyond

Baier, Moritz Friedrich (2018)

In this thesis, a fully integrated dual-polarization (DP) optical transmitter is proposed, developed and demonstrated. The transmitter proposed in this work consists of two key building blocks: a polarization rotator (PR) and two electro-absorption modulators (EAM), laid out in a serial configuration. Furthermore, a laser source is monolithically integrated. All devices are realized in the semi...

Entwicklung von optisch pumpbaren UVC-Lasern auf AlGaN-Basis

Jeschke, Jörg (2018)

In dieser Arbeit wurde der Einfluss verschiedener Aspekte des epitaktischen Wachstums und des Heterostrukturdesigns auf optisch gepumpte AlGaN-Laser mit Emissionswellenlängen im Bereich von 240 nm untersucht. Dabei wurden neue Erkenntnisse über elektrische und optische Verlustmechanismen gewonnen, die über den konkreten Anwendungsfall hinaus für AlGaN-Heterostrukturen relevant sind. Außerdem wu...

Scanning tunneling microscopy study of strong metal-support interaction in iron oxide based model catalysts

Zhang, Ke (2018)

The term “strong metal-support interaction” (SMSI) was introduced by S.J. Tauster in late 1970’s to describe drastic changes in the chemisorption properties of metal particles supported on reducible oxides. Although there may be different explanations for SMSI effect, in the great majority of cases, it manifests itself via encapsulation of the supported metal particles by a thin oxide layer ste...

Internal electric field manipulation in nanostructures

Schlichting, Sarah Kristina (2018)

Recently, an unconventional approach [the so-called Internal-Field-Guarded-Active-Region Design (IFGARD)] for the elimination of the crystal polarization field induced quantum confined Stark effect (QCSE) in polar semiconductor heterostructures was developed. This thesis demonstrates by means of micro-photoluminescence techniques the successful tuning as well as the elimination of the QCSE in s...

Growth and characterization of antimony-based quantum dots in GaP matrix for nanomemories

Sala, Elisa Maddalena (2018)

Self-assembled Quantum Dots (QDs) have recently attracted great attention for enabling a novel type of non-volatile electronic nanomemory, the QD-Flash. Such a memory architecture represents the ultimate memory cell, exhibiting endurance and fast access times (~ns). To ensure non-volatile operation, the storage time for carriers has to be of the order of 10 years (or longer) at room temperature...

Towards simultaneous improvements of storage and erase times in quantum dot-based memories

Arikan, Ismail Firat (2018)

This work attempts to improve memory devices based on self-organized semiconductor quantum dots (QDs) in two ways. The first aim is to increase the hole storage time at room temperature in such a memory (QD-Flash) to achieve non-volatility. Hence, the electronic properties of QDs, such as the localization energy and the capture cross section, are determined by static capacitance-voltage (C-V) s...

Multimode optical feedback dynamics of InAs/GaAs quantum-dot lasers emitting on different lasing states

Huang, H. ; Arsenijević, D. ; Schires, K. ; Sadeev, T. ; Bimberg, D. ; Grillot, F. (2016)

Quantum dot lasers are envisioned to be the next generation of optical transmitters used for short-reach communication links, owing to their low threshold current and high temperature operation. However, in a context of steady increase in both speed and reach, quantum dot lasers emitting on their upper energy levels have been recently of greater interest as they are touted for their faster modu...

Efficiency of four-wave mixing in injection-locked InAs/GaAs quantum-dot lasers

Huang, H. ; Arsenijević, D. ; Schires, K. ; Sadeev, T. ; Erasme, D. ; Bimberg, D. ; Grillot, F. (2016)

Frequency conversion using highly non-degenerate four-wave mixing is investigated in optically injection-locked InAs/GaAs quantum-dot Fabry-Perot lasers with different ridge waveguide dimensions. Conversion efficiencies up to -16 dB with a large optical signal-to-noise ratios of 36 dB are unveiled. The conversion bandwidth is extended to 4 THz with a quasi-symmetrical response between up- and d...

The fate of the 2√3 × 2√3R(30°) silicene phase on Ag(111)

Liu, Zhi-Long ; Wang, Mei-Xiao ; Liu, Canhua ; Jia, Jin-Feng ; Vogt, Patrick ; Quaresima, Claudio ; Ottaviani, Carlo ; Olivieri, Bruno ; Padova, Paola de ; Lay, Guy Le (2014)

Silicon atoms deposited on Ag(111) produce various single layer silicene sheets with different buckling patterns and periodicities. Low temperature scanning tunneling microscopy reveals that one of the silicene sheets, the hypothetical √7 × √7 silicene structure, on 2√3 × 2√3 Ag(111), is inherently highly defective and displays no long-range order. Moreover, Auger and photoelectron spectroscopy...

Epitaxial growth of GaN quantum dots on smooth AlN

Bellmann, Konrad (2018)

A fundamental limitation of current quantum dot based monolithic quantum-devices emitting single or entangled photons is the operation at cryogenic temperatures. A straightforward solution is the use of group-III nitrides. In particular, the large bandgap difference between the two binary compounds GaN and AlN of 2.6 eV can provide superior exciton confinement for an energy separation between d...

Nitrogen and vacancy clusters in ZnO

Tuomisto, Filip ; Rauch, Christian ; Wagner, Markus R. ; Hoffmann, Axel ; Eisermann, Sebastian ; Meyer, Bruno K. ; Kilanski, Lukasz ; Tarun, Marianne C. ; McCluskey, Matthew D. (2013)

Understanding the interaction of group V impurities with intrinsic defects in ZnO is important for developing p-type material. We have studied N-doped ZnO thin films and N-doped bulk ZnO crystals, with positron annihilation spectroscopy, in contrast to earlier studies that have concentrated on N-implanted ZnO crystals. We show that the introduction of N impurities into ZnO, irrespective of whet...

Coherently-driven exciton polaritons and directional cQED effects in the quantum dot-micropillar system

Hopfmann, Caspar (2018)

Cavity quantum electrodynamic (cQED) systems have attracted extensive research interest in the past decades as the main driving force of quantum optics. First experimental demonstrations focused on the enhancement of spontaneous emission and optical nonlinearities related to a single quantum emitter confined in a microcavity. Major technological effort was needed to enter the strong coupling re...

Novel high-power and high-brightness semiconductor lasers with ultra-narrow vertical beam divergence

Miah, Md. Jarez (2018)

This doctoral thesis focuses on the realization of high-power and high-brightness 1060 nm edge-emitting lasers grown on a GaAs substrate. Two different types of lasers have been successfully implemented, namely PBC (PBC: photonic band crystal) and HiBBEE (HiBBEE: high-brightness vertical broad-area edge-emitting) lasers. To reduce the typical large vertical beam divergence of ~ 30-60° of conven...

Accessing the dark exciton spin in deterministic quantum-dot microlenses

Heindel, Tobias ; Thoma, Alexander ; Schwartz, Ido ; Schmidgall, Emma R. ; Gantz, Liron ; Cogan, Dan ; Strauß, Max ; Schnauber, Peter ; Gschrey, Manuel ; Schulze, Jan-Hindrik ; Strittmatter, Andre ; Rodt, Sven ; Gershoni, David ; Reitzenstein, Stephan (2017)

The dark exciton state in semiconductor quantum dots (QDs) constitutes a long-lived solid-state qubit which has the potential to play an important role in implementations of solid-state-based quantum information architectures. In this work, we exploit deterministically fabricated QD microlenses which promise enhanced photon extraction, to optically prepare and read out the dark exciton spin and...