A5061252401- Advanced Electron Microscopy Techniques and Applications
- GaN-based semiconductor devices and materials
- Semiconductor Quantum Structures and Devices
- Electron and X-Ray Spectroscopy Techniques
- ZnO doping and properties
- Nanowire Synthesis and Applications
- Semiconductor materials and devices
- Advanced X-ray Imaging Techniques
- Integrated Circuits and Semiconductor Failure Analysis
- Ga2O3 and related materials
- Surface and Thin Film Phenomena
- Quantum Dots Synthesis And Properties
- Crystallography and Radiation Phenomena
- Semiconductor materials and interfaces
- Magnetic properties of thin films
- Force Microscopy Techniques and Applications
- Chalcogenide Semiconductor Thin Films
- Metallic Glasses and Amorphous Alloys
- Acoustic Wave Resonator Technologies
- Metal and Thin Film Mechanics
- Advanced Semiconductor Detectors and Materials
- Photonic and Optical Devices
- Ferroelectric and Negative Capacitance Devices
- Perovskite Materials and Applications
- Physics of Superconductivity and Magnetism
Technische Universität Berlin
2015-2025
Brandenburg University of Technology Cottbus-Senftenberg
2015
University of Göttingen
2004-2010
TU Dresden
2009
Hafnium oxide (HfO x )‐based memristive devices have tremendous potential as nonvolatile resistive random access memory (RRAM) and in neuromorphic electronics. Despite its seemingly simple two‐terminal structure, a myriad of RRAM reported the rapidly growing literature exhibit rather complex switching behaviors. Using Pt/HfO /TiN‐based metal–insulator–metal structures model systems, it is shown that well‐controlled oxygen stoichiometry governs filament formation occurrence multiple modes....
We report on III-Nitride blue light emitting diodes (LEDs) comprising a GaN-based tunnel junction (TJ) all realized by metalorganic vapor phase epitaxy in single growth process. The TJ grown atop the LED structures consists of Mg-doped GaN layer and subsequently highly Ge-doped GaN. Long thermal annealing 60 min at 800 °C is important to reduce series resistance LEDs due blockage acceptor-passivating hydrogen diffusion through n-type doped top layer. Secondary ion mass spectroscopy...
Many material properties are governed by dislocations and their interactions. The reconstruction of the three-dimensional structure a dislocation network so far is mainly achieved tomographic tilt series with high angular ranges, which experimentally challenging additionally puts constraints on possible specimen geometries. Here, we show way to reveal three dimensional location simultaneously classify type from single 4D scanning transmission electron microscopy measurements. dislocation's...
Many material properties can be tuned by strain fields within the specimen. Examples range from mechanical of alloy hardening to electro-optical like emission wavelengths in semiconductor heterostructure quantum wells. While several transmission electron microscopy techniques for measurements these exists, typically neglect variations along beam or try mitigate their effects. Here we investigated effects inhomogeneities direction under dynamical diffraction conditions. We performed scanning...
Single crystal ZnO wurtzite nanowires grown along the c-axis with diameters down to 4 nm were synthesized by a catalytic vapor transport technique. Photoluminescence spectra of these wires indicate blue shift free exciton 19 meV due confinement. This result was obtained analyzing line shape blue-shifted LO phonon replica exciton. In addition, surface-related excitonic luminescence feature centered at 3.366 eV observed strongly elevated thermal activation energy.
We investigate the size dependence of exciton-LO-phonon coupling strength in colloidal CdSe nanorods coated with an epitaxial ZnS shell. find increase decreasing nanorod diameter. The growth a shell on surface much more strongly reduces exciton-phonon than expected from geometry considerations. determined radius Huang-Rhys factor is similar to that observed for spherical nanocrystals.
Unveiling the physical nature of oxygen-deficient conductive filaments (CFs) that are responsible for resistive switching HfO2-based random access memory (RRAM) devices represents a challenging task due to oxygen vacancy related defect and nanometer size CFs. As first important step this goal, we demonstrate in work direct visualization study physico–chemical properties amorphous HfO2−x by carrying out transmission electron microscopy holography as well energy dispersive x-ray spectroscopy...
Dislocation networks are one of the most principle sources deteriorating performances devices based on lattice-mismatched heteroepitaxial systems. We demonstrate here a technique enabling fully coherent germanium (Ge) islands selectively grown nanotip-patterned Si(001) substrates. The silicon (Si)-tip-patterned substrate, fabricated by complementary metal oxide semiconductor compatible nanotechnology, features ∼50-nm-wide Si areas emerging from SiO2 matrix and arranged in an ordered lattice....
Abstract The integration of dislocation-free Ge nano-islands was realized via selective molecular beam epitaxy on Si nano-tip patterned substrates. Si-tip wafers feature a rectangular array nanometer sized tips with (001) facet exposed among SiO 2 matrix. These were fabricated by complementary metal-oxide-semiconductor (CMOS) compatible nanotechnology. Calculations based nucleation theory predict that the growth occurs close to thermodynamic equilibrium, where condensation adatoms is...
The non-destructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms functional potentials is crucial for correlating device properties with their morphological/materials features, well precisely tuning and optimizing growth process. Electron holographic tomography (EHT) has been used the past to reconstruct total potential distribution 3D but hitherto lacked a quantitative approach separate variations due chemical composition changes (mean...
The epitaxial integration of highly heterogeneous material systems with silicon (Si) is a central topic in (opto-)electronics owing to device applications. InP could open new avenues for the realization novel devices such as high-mobility transistors next-generation CMOS or efficient lasers Si photonics circuitry. However, InP/Si heteroepitaxy challenging due lattice (∼8%), thermal expansion mismatch (∼84%), and different symmetries. Here, we demonstrate growth nanocrystals showing high...
We report on the development of electron holographic tomography towards a versatile potential measurement technique, overcoming several limitations, such as limited tilt range, previously hampering reproducible and accurate electrostatic reconstruction in three dimensions. Most notably, tomographic is performed optimally sampled polar grids taking into account symmetry other spatial constraints nanostructure. Furthermore, series acquisition alignment have been automated adapted to...
While electron holography in the transmission microscope offers possibility to measure maps of electrostatic potential semiconductors down nanometer dimensions, these measurements are known underestimate absolute value potential, especially GaN. We have varied dose rates irradiation over several orders magnitude and observed strong variations holographically detected voltages. Overall, results indicate that beam generates electrical currents within specimens primarily by photovoltaic effect...
Abstract Complex 3D magnetic textures in nanomagnets exhibit rich physical properties, e.g., their dynamic interaction with external fields and currents, play an increasing role for current technological challenges such as energy-efficient memory devices. To study these nanostructures including dependency on geometry, composition, crystallinity, a characterization of the field nanometer spatial resolution is indispensable. Here we show how holographic vector electron tomography can...
Thin-film solar cells based on Cu(In,Ga)Se2 (CIGSe) reach high power-conversion efficiencies in spite of large dislocation densities up to 1010–1011 cm−2. The present work gives insight into the structural and compositional properties dislocations CIGSe thin films, which are embedded a complete cell stack. These related average electrical potential distributions obtained by means inline electron holography. At part studied, electrostatic shows local minima, all with depths about −1.4 V....
We report on a characteristic photoluminescence feature of the substitutional Mn in high quality GaMnN layers. The lattice site was identified using atom localization by channeling enhanced microanalysis with transmission electron microscope. It shows that 96.5%±5.0% atoms are incorporated Ga site. In appears at 1.41 eV phonon sideband related to GaN matrix. temperature evolution is an intra-atomic transition and it assigned internal E5→T52 Mn3+ ion. assignment supported absorption...
Abstract In this work the vibrational properties of colloidal CdSe nanorods (NRs) and CdSe‐ZnS core–shell NRs are investigated via Raman spectroscopy. The longitudinal optical (LO) phonons in confined to NR volume. confinement phonon wave function leads a relaxation q = 0 rule frequency is found depend on diameter. coupling strength between LO excitons also depends total much lower than bulk material due decrease influence Coulomb interaction nanoparticles. However, rise for decreasing...