Inst. Festkörperphysik

169 Items

Recent Submissions
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...

Infrared ellipsometry on mixed functional polymer brushes designed to control surface characteristics

Kroning, Annika (2017)

The present work deals with the optical characterization of temperature-responsive polymer brushes. It is part of a DFG-funded project to study responsive surfaces that aims to use these for substrates in tissue engineering. The used polymers are poly(2-cyclopropyl-2-oxazoline) [PcPrOx] and the well-studied poly(N-isopropylacrylamide) [PNIPAAm], that both exhibit a lower critical solution tempe...

Strain-phase relations in lead-free ferroelectric KxNa1-xNbO3 epitaxial films for domain engineering

Braun, Dorothee (2017)

The aim of this thesis is to demonstrate the potential of thin films for technical applications by tuning the ferroelectric film properties on the basis of the strain-phase diagram. For this purpose, a fundamental understanding of the relation between incorporated lattice strain by epitaxial growth of thin films and the evolution of ferroelectric phases has been pointed out. As an exemplary lea...

Photolumineszenz- und Raman-Spektroskopie von zweidimensionalem MoS2

Scheuschner, Nils (2017)

In this work the electronic and vibrational properties of two-dimensional molybdenum disulfide (MoS2) are examined using Raman- and photoluminescencespectroscopy (PL). Spatially resolved measurements of suspended MoS2 and Si/SiO2 supported MoS2 show an increase of the charge carrier concentration of the MoS2 in the supported areas. Furthermore the indirect band gap energy of bilayer MoS2 is dec...

Unconventional magnetic properties of low-dimensional antiferromagnets BaNi2V2O8 and BaCu2V2O8

Klyushina, Ekaterina (2017)

This work explores the magnetic properties of two novel compounds BaCu2V2O8 and BaNi2V2O8 which both provide rare physical realizations of model magnetic systems that are characterized by unconventional magnetic behaviour at finite temperatures. BaNi2V2O8 has an ideal honeycomb crystal structure where S=1 nickel magnetic ions are arranged on well isolated honeycomb layers. The nearest neighbour...

Magnetic properties of rare earth zirconate pyrochlores

Xu, Jianhui (2017)

Diese Dissertation behandelt experimentelle Untersuchungen an drei magnetischen Pyrochloren, Nd2Zr2O7, Sm2Zr2O7 and Gd2Zr2O7. Es wurden einkristalline und pulverförmige Proben hergestellt wobei die zwei erstgenannten Substanzen in der Pyrochlor Struktur kristallisieren, während Gd2Zr2O7 einige Platzwechsel-Defekte von Gd/Zr aufweist. Alle Verbindungen zeigen in den makroskopischen Eigenschaften...

Effects of magnetic field gradients on the aggregation dynamics of colloidal magnetic nanoparticles

Heinrich, Dirk ; Goñi, Alejandro R. ; Osán, Tristán ; Cerioni, L. M. C. ; Smessaert, Anton ; Klapp, Sabine H. L. ; Faraudo, Jordi ; Pusiol, Daniel Jose ; Thomsen, Christian (2015)

We have used low-field H-1 nuclear-magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) to investigate the aggregation dynamics of magnetic particles in ionic ferrofluids (IFFs) in the presence of magnetic field gradients. At the beginning of the experiments, the measured NMR spectra were broad and asymmetric, exhibiting two features attributed to different dynamical environments o...

Design, Epitaxie und Charakterisierung AlGaN-basierter Leuchtdioden mit Emissionswellenlängen unterhalb von 250 nm

Mehnke, Frank (2017)

Diese Arbeit befasst sich mit der Realisierung von AlGaN-basierten ultravioletten Leuchtdioden (LEDs) mit Emissionswellenlängen unterhalb von 250 nm sowie der Analyse ihrer strukturellen und elektrooptischen Eigenschaften. Ziel war es, eine LED mit einer mit möglichst maximaler spektraler Leistungsdichte bei 226 nm zu realisieren, welche es ermöglicht, Absorptionsmessungen innerhalb eines Stick...

Towards non-volatility in quantum-dot-based memories

Bonato, Leo (2017)

The aim of this work is the extension of the hole storage time at room temperature in self-organised semiconductor quantum dots (QDs), with the long-term goal of achieving non-volatility in said QDs in order to develop a novel charge-storage memory architecture. Static capacitance spectroscopy (C--V profiling) and time-resolved capacitance spectroscopy (deep level transient spectroscopy, DLTS) ...

Periodic lateral polar structure-based waveguides in III-nitrides for quasi-phase matched second harmonic generation

Alden Angeles, Dorian Eduardo (2017)

Lasers emitting in the ultraviolet spectrum below 300 nm are desired for a variety of applications. Currently available deep UV laser systems are expensive, inefficient, stationary, require frequent maintenance and have a high operation cost. Alternatively, UV laser light can be obtained through frequency doubling as second harmonic generation using nonlinear crystals. The III-Nitrides are attr...

Blind testing of cross-linking/mass spectrometry hybrid methods in CASP11

Schneider, Michael ; Belsom, Adam ; Rappsilber, Juri ; Brock, Oliver (2016)

Hybrid approaches combine computational methods with experimental data. The information contained in the experimental data can be leveraged to probe the structure of proteins otherwise elusive to computational methods. Compared with computational methods, the structures produced by hybrid methods exhibit some degree of experimental validation. In spite of these advantages, most hybrid methods h...