7 results on '"Martin Eickhoff"'
Search Results
2. Effects of interface geometry on the thermoelectric properties of laterally microstructured ZnO-based thin films
- Author
-
A. Kronenberger, G. Homm, S. Petznick, Peter J. Klar, Bruno K. Meyer, Christian Heiliger, T. Henning, F. Gather, and Martin Eickhoff
- Subjects
Materials science ,Condensed matter physics ,Bar (music) ,Surfaces and Interfaces ,Power factor ,Condensed Matter Physics ,Epitaxy ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Electrical resistivity and conductivity ,Seebeck coefficient ,Thermoelectric effect ,Materials Chemistry ,Perpendicular ,Electrical and Electronic Engineering ,Thin film - Abstract
A series of samples consisting of alternating stripes of ZnO grown by molecular-beam epitaxy (MBE) and radio-frequency (rf) sputtered Ga-doped ZnO stripes was laterally microstructured with a self-aligned pattern transfer method. We measured as a function of temperature the Seebeck coefficient S and the electrical resistivity ρ in-plane of the samples with the transport direction perpendicular to the stripe direction. Throughout the series the bar width and hence the number of interfaces was kept constant, but the interface profile was varied yielding different interface lengths and geometries. The dependence of S, ρ and the power factor S2/ρ on the interface length at room temperature were simulated using an empirical network model and it was demonstrated that the macroscopic transport coefficients are very sensitive to the interface region and that even this rather simple modelling yields useful information about the interface region.
- Published
- 2012
3. Strain effects and phonon-plasmon coupled modes in Si-doped AlN
- Author
-
Ana Cros, M. Gómez-Gómez, Martin Eickhoff, Martin Stutzmann, and M. Hermann
- Subjects
Materials science ,Condensed matter physics ,Silicon ,Phonon ,Doping ,Analytical chemistry ,chemistry.chemical_element ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Blueshift ,symbols.namesake ,chemistry ,Materials Chemistry ,symbols ,Sapphire ,Crystalline silicon ,Electrical and Electronic Engineering ,Raman spectroscopy ,Raman scattering - Abstract
The E 2h and A 1 (LO) phonon modes of AlN films grown on sapphire are analyzed by Raman scattering as a function of silicon doping for concentrations covering from 5.5 x 10 19 cm ―3 to 5.2 x 10 21 cm ―3 . For high doping levels the appearance of a mode around 520 cm ―1 indicates the precipitation of crystalline silicon in the samples and its inhomogeneous incorporation to the AlN layer. The frequency of this mode shifts to lower energies with doping, indicating that the silicon crystals are embedded in the AlN lattice and under tensile strain. On the other hand, the AlN phonon modes are blue-shifted due to the compressive strain as a result of the silicon incorporation. This strain is partially relieved for very high doping levels. The coupling of the polar A 1 (LO) mode of the AlN films with the electronic cloud (phonon―plasmon coupling) is analyzed for electron concentrations up to 4 × 10 17 cm ― 3 . A 2 cm ―1 blue shift of the phonon frequencies is observed for the highest electron concentrations.
- Published
- 2009
4. Analysis of polarization-dependent photoreflectance studies forc-plane GaN films grown ona-plane sapphire
- Author
-
Norbert Esser, Florian Furtmayr, Rüdiger Goldhahn, C. Buchheim, Marcus Röppischer, Christoph Cobet, Martin Eickhoff, and Thomas Wassner
- Subjects
Photoluminescence ,Condensed matter physics ,Chemistry ,Gallium nitride ,Surfaces and Interfaces ,Substrate (electronics) ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Electric field ,Materials Chemistry ,Sapphire ,Electrical and Electronic Engineering ,Thin film ,Anisotropy ,Molecular beam epitaxy - Abstract
The optical properties of c-plane GaN layers grown by molecular beam epitaxy on a-plane sapphire substrate are investigated. Polarization-dependent photoreflectance spectroscopy was applied with the electric field vector of the probe beam being either parallel or perpendicular to the [10 10] direction of the GaN films. A pronounced in-plane optical anisotropy under normal incidence of light is observed which is attributed to anisotropic in-plane strain. It originates from the difference of the thermal expansion coefficients of the substrate parallel and perpendicular to its c-axis. Temperaturedependent studies and a comparison to photoluminescence and reflectance anisotropy studies indicate that the strain (anisotropy) increases with decreasing sample temperature. The dependence of transition energies and oscillator strengths of GaN as a function of strain values is calculated by k·p perturbation theory for comparison. The results emphasize the experimental data.
- Published
- 2009
5. Modulation spectroscopy of AlGaN/GaN heterostructures: The influence of electron-hole interaction
- Author
-
Armin Dadgar, O. Weidemann, A. T. Winzer, Martin Eickhoff, Alois Krost, and Rüdiger Goldhahn
- Subjects
Condensed matter physics ,Chemistry ,Exciton ,Heterojunction ,Surfaces and Interfaces ,Electron hole ,Dielectric ,Condensed Matter Physics ,Franz–Keldysh effect ,Spectral line ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Barrier layer ,Materials Chemistry ,Electrical and Electronic Engineering ,Fermi gas - Abstract
A detailed analysis of electroreflectance (ER) spectra for AlGaN/GaN heterostructures containing a two-dimensional electron gas (2DEG) is presented. The properties of two samples with different Al-content in the barrier layer are compared. Calculated field-dependent dielectric functions (DF) for GaN and AlGaN which take into account electron-hole interaction (exciton effects) provide the basis for the modeling of the spectra. It is demonstrated that the Seraphin coefficients exhibit a strong spectral dependence around the gap which cannot be neglected in a fit of ER spectra. The use of the calculated DFs in a multi-layer model allows to reproduce all peculiarities of experimental ER spectra for both, the GaN channel layer and the AlGaN barrier layer, despite the inhomogeneous field distribution. The determined AlGaN barrier field strengths are very close to the values obtained by applying the asymptotic formulation of the Franz-Keldysh effect. Finally, the polarization gradient at the AlGaN/GaN boundary is estimated from these field strengths. The gradient is slightly lower than theoretically predicted which confirms previous studies.
- Published
- 2007
6. Direct biofunctionalization of semiconductors: A survey
- Author
-
Jose A. Garrido, Martin Eickhoff, Martin Stutzmann, and Martin S. Brandt
- Subjects
Physics ,business.industry ,Semiconductor materials ,Nanotechnology ,Material system ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Organic molecules ,Preparation method ,Semiconductor ,Basic research ,Materials Chemistry ,Electrical and Electronic Engineering ,business - Abstract
Received 24 October 2006, accepted 30 October 2006 Published online 10 November 2006 PACS 68.35.–p, 68.47.Fg, 73.30.+y, 81.07.Pr, 82.47.Rs The covalent attachment of small organic molecules and larger functional biomolecules such as DNA, en-zymes, or other proteins on semiconductors is a new field of basic research with a pronounced interdisci-plinary flavour. The ultimate goal of this endeavour is the creation of novel organic/inorganic heterostruc-tures which can provide a direct link between the complex worlds of biology and digital electronics on a nanometer scale. The purpose of the present survey is to provide an overview over basic physics aspects, preparation methods, as well as possible applications of biofunctionalized semiconductors based on dif-ferent material systems.
- Published
- 2006
7. Thermoresistive and Piezoresistive Properties of Wurtzite N-GaN
- Author
-
Paolo Visconti, A. Rizzi, Annalisa Bonfiglio, Martin Eickhoff, S. Mingiacchi, Gennaro Conte, Paolo Lugli, Oliver Ambacher, R. Cingolani, Adriana Passaseo, S., Mingiacchi, A., Bonfiglio, G., Conte, M., Eickhoff, O., Ambacher, A., Rizzi, A., Passaseo, Visconti, Paolo, R., Cingolani, and P., Lugli
- Subjects
Materials science ,Gauge factor ,Thermistor ,Analytical chemistry ,Mineralogy ,Metalorganic vapour phase epitaxy ,Condensed Matter Physics ,Piezoresistive effect ,Temperature coefficient ,Temperature measurement ,Order of magnitude ,Electronic, Optical and Magnetic Materials ,Wurtzite crystal structure - Abstract
We performed thermo and piezoresistive measurements on GaN bulk samples grown with different techniques (PIMBE, MOCVD). By analysing the I(V) characteristics as a function of temperature, we found a temperature coefficient of resistance (TCR = a) of the same order of magnitude (a few percent per °C) as commercial thermistors, with a peak value of 19%/°C. The measured gauge factor is about five, a value comparable with that obtained for GaN by other groups. We also performed PC vs. temperature measurements on a MQW GaN/AlGaN finding a peak shift of about 0.4 meV/K.
- Published
- 2002
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.