@article{13520, abstract = {{Atomistic simulations in the framework of the density functional theory have been used to model morphologic and vibrational properties of lithium niobate–lithium tantalate mixed crystals as a function of the [Nb]/[Ta] ratio. Structural parameters such as the crystal volume and the lattice parameters a and c vary roughly linearly from LiTaO3 to LiNbO3, showing only minor deviations from the Vegard behavior. Our ab initio calculations demonstrate that the TO1, TO2 and TO4 vibrational modes become harder with increasing Nb concentration. TO3 becomes softer with increasing Nb content, instead. Furthermore, the investigated zone center A1 -TO phonon modes are characterized by a pronounced stoichiometry dependence. Frequency shifts as large as 30 cm−1 are expected as the [Nb]/[Ta] ratio grows from 0 to 1. Therefore, spectroscopic techniques sensitive to the A1 modes (such as Raman spectroscopy), can be employed for a direct and non-destructive determination of the crystal composition.}}, author = {{Sanna, Simone and Riefer, A. and Neufeld, Sergej and Schmidt, Wolf Gero and Berth, Gerhard and Rüsing, Michael and Widhalm, A. and Zrenner, Artur}}, issn = {{0015-0193}}, journal = {{Ferroelectrics}}, keywords = {{Ferroelectrics, vibrational properties, LiNbO3, LiTaO3, mixed crystals}}, number = {{1}}, pages = {{63--68}}, title = {{{Vibrational Fingerprints of LiNbO3-LiTaO3Mixed Crystals}}}, doi = {{10.1080/00150193.2013.821893}}, volume = {{447}}, year = {{2013}}, } @article{4353, author = {{Schumacher, Stefan and Zrenner, Artur}}, issn = {{0277-786X}}, journal = {{ULTRAFAST PHENOMENA AND NANOPHOTONICS XVII}}, title = {{{Two-photon physics with quantum-dot biexcitons}}}, doi = {{10.1117/12.2004191}}, year = {{2013}}, } @inproceedings{4380, abstract = {{The structural and vibrational properties of lithium niobate (LN) – lithium tantalate (LT) mixed crystals (LNT, LiNb1-xTaxO3) are investigated over the whole composition range by first-principles simulations. The crystal volume grows roughly linearly from LT to LN, whereby the lattice parameters a and c show minor deviations from the Vegard behavior between the end compounds, LiNbO3 and LiTaO3. Our calculations in the framework of the density functional theory show the TO1, TO2 and TO4-modes to become harder with increasing Nb concentration. TO3 becomes softer with increasing Nb content, instead. The frequency shifts of the zone center A1-TO phonon modes for crystals with different compositions are found to be as large as 30 cm-1. Raman spectroscopy, which is sensitive to the A1 modes, can be therefore employed to determine the crystal composition.}}, author = {{Sanna, Simone and Riefer, Arthur and Neufeld, Sergej and Schmidt, Wolf Gero and Berth, Gerhard and Widhalm, Alex and Zrenner, Artur}}, booktitle = {{Proceedings of ISAF-ECAPD-PFM 2012}}, keywords = {{Ferroelectrics, Vibrational properties, LiNbO3, LiTaO3, Mixed Crystals}}, location = {{Aveiro, Portugal}}, title = {{{Vibrational fingerprints of LiNbO3-LiTaO3 mixed crystals}}}, year = {{2012}}, } @inbook{4381, abstract = {{Coherent physics and applications of exciton qubits in electric fi eld tunable quantum dot structures are our focus. Excitations with picosecond (ps) laser pulses result in qubit rotations. Using state projection by tunnelling the readout can be performed in quantitative way. As a function of electric fi eld induced detuning Ramsey fringes of a single exciton qubit can be observed and controlled for double pulse excitation. Therefore it is possible to demonstrate voltage controlled qubit manipulations within a wide range of pulse delays. Using fast electric signals, phase-locked to ps-laser pulses, the coherent control of an exciton qubit can be obtained by electric interaction. Such voltage controlled qubit manipulations seem to be essential for new types of optoelectronic quantum gates and novel applications in the fi eld of coherent optoelectronics.}}, author = {{Michaelis de Vasconcellos, Steffen and Gordon, Simon and Mantei, Dirk and Leier, Yves Alexander and Al-Hmoud, M. and Quiring, Wadim and Zrenner, Artur}}, booktitle = {{QUANTUM OPTICS WITH SEMICONDUCTOR NANOSTRUCTURES}}, editor = {{Jahnke, Frank}}, isbn = {{9780857092328 0857092324}}, keywords = {{excitons, quantum bits, coherent manipulation, Ramsey interference, quantum gate}}, pages = {{528--559}}, publisher = {{Woodhead Publishing}}, title = {{{Coherent optoelectronics with quantum dots}}}, year = {{2012}}, } @article{3974, abstract = {{We study the quantum properties and statistics of photons emitted by a quantum-dot biexciton inside a cavity. In the biexciton-exciton cascade, fine-structure splitting between exciton levels degrades polarization-entanglement for the emitted pair of photons. However, here we show that the polarization-entanglement can be preserved in such a system through simultaneous emission of two degenerate photons into cavity modes tuned to half the biexciton energy. Based on detailed theoretical calculations for realistic quantum-dot and cavity parameters, we quantify the degree of achievable entanglement.}}, author = {{Schumacher, Stefan and Förstner, Jens and Zrenner, Artur and Florian, Matthias and Gies, Christopher and Gartner, Paul and Jahnke, Frank}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_qd}}, number = {{5}}, pages = {{5335--5342}}, publisher = {{OSA}}, title = {{{Cavity-assisted emission of polarization-entangled photons from biexcitons in quantum dots with fine-structure splitting}}}, doi = {{10.1364/oe.20.005335}}, volume = {{20}}, year = {{2012}}, } @article{3972, abstract = {{Using a finite-difference time-domain method, we theoretically investigate the optical spectra of crossing perpendicular photonic crystal waveguides with quantum dots embedded in the central rod. The waveguides are designed so that the light mainly propagates along one direction and the cross talk is greatly reduced in the transverse direction. It is shown that when a quantum dot (QD) is resonant with the cavity, strong coupling can be observed via both the transmission and crosstalk spectrum. If the cavity is far off-resonant from the QD, both the cavity mode and the QD signal can be detected in the transverse direction since the laser field is greatly suppressed in this direction. This structure could have strong implications for resonant excitation and in-plane detection of QD optical spectroscopy.}}, author = {{Song, Xiaohong and Declair, Stefan and Meier, Torsten and Zrenner, Artur and Förstner, Jens}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_phc, tet_topic_qd}}, number = {{13}}, pages = {{14130--14136}}, publisher = {{The Optical Society}}, title = {{{Photonic crystal waveguides intersection for resonant quantum dot optical spectroscopy detection}}}, doi = {{10.1364/oe.20.014130}}, volume = {{20}}, year = {{2012}}, } @article{4544, abstract = {{The existence of localized vibrational modes both at the positive and at the negative LiNbO3 (0001) surface is demonstrated by means of first-principles calculations and Raman spectroscopy measurements. First, the phonon modes of the crystal bulk and of the (0001) surface are calculated within the density functional theory. In a second step, the Raman spectra of LiNbO3 bulk and of the two surfaces are measured. The phonon modes localized at the two surfaces are found to be substantially different, and are also found to differ from the bulk modes. The calculated and measured frequencies are in agreement within the error of the method. Raman spectroscopy is shown to be sensitive to differences between bulk and surface and between positive and negative surface. It represents therefore an alternative method to determine the surface polarity, which does not exploit the pyroelectric or piezoelectric properties of the material.}}, author = {{Sanna, S. and Berth, Gerhard and Hahn, W. and Widhalm, A. and Zrenner, Artur and Schmidt, W. G.}}, issn = {{0885-3010}}, journal = {{IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control}}, number = {{9}}, pages = {{1751--1756}}, publisher = {{Institute of Electrical and Electronics Engineers (IEEE)}}, title = {{{Vibrational properties of the LiNbO3 z-surfaces}}}, doi = {{10.1109/tuffc.2011.2012}}, volume = {{58}}, year = {{2011}}, } @article{4545, abstract = {{Laser irradiation damage in ZnTe epilayers was analyzed in situ by power-density-dependent and time-resolved micro-Raman spectroscopy. Damage by ablation or compound decomposition on the sample surface was revealed by the decrease of the ZnTe–nLO mode intensity with the increase of laser power density. The appearance of the peaks associated with the stronger crystalline-tellurium modes, tellurium aggregates and second-order Raman scattering at room temperature μ-Raman spectra was observed for higher power densities than 4.4 × 105 W cm−2. The Raman signal time transients of ZnTe–nLO and crystalline-tellurium modes reveal an exponential evolution of the laser irradiation damage and a fast formation of crystalline tellurium aggregates on the layer surface.}}, author = {{Wiedemeier, V and Berth, Gerhard and Zrenner, Artur and Larramendi, E M and Woggon, U and Lischka, K and Schikora, D}}, issn = {{0268-1242}}, journal = {{Semiconductor Science and Technology}}, number = {{10}}, publisher = {{IOP Publishing}}, title = {{{In situ characterization of ZnTe epilayer irradiation via time-resolved and power-density-dependent Raman spectroscopy}}}, doi = {{10.1088/0268-1242/26/10/105023}}, volume = {{26}}, year = {{2011}}, } @inproceedings{4546, abstract = {{Silicon oxynitride (SiON) layers for telecommunication device application are grown by Plasma Enhanced Chemical Vapor Deposition (PECVD) for various gas compositions of SiH4, N2O and NH3. Processing and annealing effects on the oxynitride films were studied by Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM) measurements. By reduction of the silane (SiH4) gas flow and enhancement of the PECVD deposition temperature, the absorption loss due to NH bands can be nearly completely erased. Furthermore the surface roughness can be reduced by decreasing the gas flow and rising the deposition temperature. First waveguide structures are introduced and their characterization is presented.}}, author = {{Frers, Torsten and Hett, Thomas and Hilleringmann, Ulrich and Berth, Gerhard and Widhalm, Alex and Zrenner, Artur}}, booktitle = {{2011 Semiconductor Conference Dresden}}, isbn = {{9781457704314}}, location = {{Dresden, Germany}}, publisher = {{IEEE}}, title = {{{Characterization of SiON integrated waveguides via FTIR and AFM measurements}}}, doi = {{10.1109/scd.2011.6068744}}, year = {{2011}}, } @misc{4171, abstract = {{The method involves exciting a quantum system with photons in a polarization state. Two states of the quantum system are excited with linear horizontal and vertical polarizations that are orthogonal to each other, where the states exhibit an energetic gap smaller than energetic bandwidth of photons. The states are assigned based on the polarizations, where the quantum system is arranged in a superposition state. The quantum system is formed by a quantum bit that is formed as a two-level system.}}, author = {{Förstner, Jens and Mantei, D. and de Vasconcellos, S. Michaelis and Zrenner, Artur}}, keywords = {{tet_topic_qd}}, title = {{{Method for transmission of information about polarization state of photons to stationary system}}}, year = {{2011}}, } @article{4377, abstract = {{Confocal Raman spectroscopy was performed as an archetype imaging method to study the ferroelectric domain structure of periodically poled lithium niobate. More precisely, the linkage out of spatial resolution and spectral information proved itself as very useful. Here a specific modulation of the Raman lines by the local variation of polarity and a non-symmetric measuring-signal across the domain structure were found, which allows for imaging of domain boundaries as well as oppositely orientated domains. The high potential of this method is demonstrated by the visualization of the ferroelectric domain structures based on various phonon modes.}}, author = {{Berth, Gerhard and Hahn, Wjatscheslaw and Wiedemeier, Volker and Zrenner, Artur and Sanna, Simone and Schmidt, Wolf Gero}}, issn = {{0015-0193}}, journal = {{Ferroelectrics}}, keywords = {{Raman spectroscopy, ferroelectric domains, LiNbO3, confocal imaging}}, number = {{1}}, pages = {{44--48}}, publisher = {{Informa UK Limited}}, title = {{{Imaging of the Ferroelectric Domain Structures by Confocal Raman Spectroscopy}}}, doi = {{10.1080/00150193.2011.594774}}, volume = {{420}}, year = {{2011}}, } @article{4378, abstract = {{Using a combined all-ultra-high-vacuum process employing lateral patterning with focused ion beams and molecular beam epitaxy, site-selective growth of single (In,Ga)As quantum dots is achieved. We have embedded such a layer of intentionally positioned quantum dots in the intrinsic region of a p-i-n junction so that the quantum dots can be driven electrically. In this contribution, we will present our results on the morphological properties of the ion-beam modified surface on which the quantum dot nucleation occurs together with a characterization of the electrical and optoelectronic properties. We will demonstrate that a single, individual quantum dot can directly be electrically addressed.}}, author = {{Mehta, Minisha and Reuter, Dirk and Wieck, Andreas D. and Michaelis de Vasconcellos, Steffen and Zrenner, Artur and Meier, Cedrik}}, issn = {{1862-6351}}, journal = {{physica status solidi (c)}}, keywords = {{molecular beam epitaxy, quantum dot, site control, electroluminescence}}, number = {{4}}, pages = {{1182--1185}}, publisher = {{Wiley}}, title = {{{Electrically driven intentionally positioned single quantum dot}}}, doi = {{10.1002/pssc.201000828}}, volume = {{8}}, year = {{2011}}, } @article{4379, abstract = {{Uniform mesoporous Si double layers are formed on 4 inch p-type < 100> wafers with an off orientation of 6º towards < 111> by means of electrochemical etching in ethanoic-based HF electrolytes. These substrates are of interest for the epitaxial growth of III–V compound semiconductor stacks on their top for the production of multi-junction solar cells and very thin electronic devices. We demonstrate transfer of porous layers after an annealing process in hydrogen atmosphere. Electron Back-Scatter Diffraction analysis confirms that the substrate orientation is conserved during the etching and annealing steps. Confocal μ-Raman spectroscopy analysis shows a decrease in the Raman signal intensity after etching and a subsequent increase after annealing while no shift is observed. By means of Atomic Force Microscopy, analysis the surface appearance after the etching and annealing steps can be visualized. The mean surface roughness varies during the process from 0.55 nm for the unprocessed wafers to 0.27 nm after etching and 0.78 nm after annealing. The decrease of average roughness after etching is caused by an electropolishing step prior to porous formation. Despite of slight increase of mean surface roughness after annealing the samples are still appropriate for high quality epitaxial growth and subsequent lift-off.}}, author = {{Garralaga Rojas, E. and Terheiden, B. and Plagwitz, H. and Hensen, J. and Wiedemeier, V. and Berth, Gerhard and Zrenner, Artur and Brendel, R.}}, issn = {{0040-6090}}, journal = {{Thin Solid Films}}, keywords = {{Porous Si, Layer transfer, Thin-film, Photovoltaics}}, number = {{1}}, pages = {{606--609}}, publisher = {{Elsevier BV}}, title = {{{Lift-off of mesoporous layers by electrochemical etching on Si (100) substrates with miscut of 6° off towards (111)}}}, doi = {{10.1016/j.tsf.2011.07.063}}, volume = {{520}}, year = {{2011}}, } @article{13561, author = {{Berth, Gerhard and Hahn, Wjatscheslaw and Wiedemeier, Volker and Zrenner, Artur and Sanna, Simone and Schmidt, Wolf Gero}}, issn = {{0015-0193}}, journal = {{Ferroelectrics}}, pages = {{44--48}}, title = {{{Imaging of the Ferroelectric Domain Structures by Confocal Raman Spectroscopy}}}, doi = {{10.1080/00150193.2011.594774}}, volume = {{420}}, year = {{2011}}, } @article{13823, author = {{Sanna, S. and Berth, Gerhard and Hahn, W. and Widhalm, A. and Zrenner, Artur and Schmidt, Wolf Gero}}, issn = {{0885-3010}}, journal = {{IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control}}, number = {{9}}, pages = {{1751--1756}}, title = {{{Vibrational properties of the LiNbO3 z-surfaces}}}, doi = {{10.1109/tuffc.2011.2012}}, volume = {{58}}, year = {{2011}}, } @article{4040, abstract = {{We numerically investigate the interaction dynamics of coupled cavities in planar photonic crystal slabs in different configurations. The single cavity is optimized for a long lifetime of the fundamental mode, reaching a Q-factor of ≈43, 000 using the method of gentle confinement. For pairs of cavities we consider several configurations and present a setup with strongest coupling observable as a line splitting of about 30 nm. Based on this configuration, setups with three cavities are investigated.}}, author = {{Declair, S. and Meier, Torsten and Zrenner, Artur and Förstner, Jens}}, issn = {{1569-4410}}, journal = {{Photonics and Nanostructures - Fundamentals and Applications}}, keywords = {{tet_topic_phc}}, number = {{4}}, pages = {{345--350}}, publisher = {{Elsevier BV}}, title = {{{Numerical analysis of coupled photonic crystal cavities}}}, doi = {{10.1016/j.photonics.2011.04.012}}, volume = {{9}}, year = {{2011}}, } @article{4543, abstract = {{The vibrational properties of the LiNbO3 (0001) surfaces have been investigated both from first principles and with Raman spectroscopy measurements. Firstly, the phonon modes of bulk and of the (0001) surface are calculated by means of the density functional theory. Our calculations reveal the existence of localised vibrational modes both at the positive and at the negative surface. The surface vibrations are found at energies above and within the bulk bands. Phonon modes localised at the positive and at the negative surface differ substantially. In a second step, the Raman spectra of LiNbO3 bulk and of the two surfaces have been measured. Raman spectroscopy is shown to be sensitive to differences between bulk and surface and between positive and negative surface. The calculated and measured frequencies are in agreement within the error of the method.}}, author = {{Sanna, S. and Berth, Gerhard and Hahn, W. and Widhalm, A. and Zrenner, Artur and Schmidt, Wolf Gero}}, issn = {{0015-0193}}, journal = {{Ferroelectrics}}, number = {{1}}, pages = {{1--8}}, publisher = {{Informa UK Limited}}, title = {{{Localised Phonon Modes at LiNbO3(0001) Surfaces}}}, doi = {{10.1080/00150193.2011.594396}}, volume = {{419}}, year = {{2011}}, } @article{4548, abstract = {{A fluorescence study of acetonitrile solutions of bis(tetramethylguanidine)propane, copper(I)-iodide and [Cu(btmgp)I] was performed and the chemical reaction of the latter species with O2 was investigated at room temperature. The actual quenching process via O2 gassing was studied and an exponential dependence of the fluorescence intensity with respect to the complex concentration was observed. Furthermore the survey was deepened on time resolved fluorescence properties of solved [Cu(btmgp)I] in a wider concentration range. The applicability of this complex for O2 sensing inside a microreactor system was proven by confocal fluorescence measurements. It was shown that the investigated system can be used for oxygen sensing in the copper concentration range from 10−2 to 10−9 mol/l.}}, author = {{Herres-Pawlis, Sonja and Berth, Gerhard and Wiedemeier, Volker and Schmidt, Ludger and Zrenner, Artur and Warnecke, Hans-Joachim}}, issn = {{0022-2313}}, journal = {{Journal of Luminescence}}, keywords = {{Copper Oxygen Fluorescence quenching N donor ligands}}, number = {{10}}, pages = {{1958--1962}}, publisher = {{Elsevier BV}}, title = {{{Oxygen sensing by fluorescence quenching of [Cu(btmgp)I]}}}, doi = {{10.1016/j.jlumin.2010.05.012}}, volume = {{130}}, year = {{2010}}, } @article{4549, abstract = {{Damage caused by laser irradiation on the surface of ZnTe epilayers was studied by micro-Raman and atomic force microscopy (AFM). ZnTe LO-phonon overtones up to four order and TO + (n − 1)LO zone-center phonons were observed in the resonant micro-Raman spectra at room temperature. Discrepancies in the literature regarding the origin of two features observed at low frequencies around 120 and 140 cm−1 in the Raman spectrum of ZnTe are discussed and resolved. These Raman peaks were not detected by using a low excitation laser power density on a Zn-terminated ZnTe surface; however, with the increase of the laser power density they were found to arise irreversibly. The correspondence of these peaks in a wave number with the strongest Raman peaks of the crystalline tellurium phase and the intensity enhancement behavior with the laser power in a similar way as for CdTe strongly suggests the formation of crystalline tellurium aggregates on the layer surface due to laser irradiation damage. AFM data reveal the occurrence of laser ablation on the ZnTe surface even though the surface temperature of the sample is below the melting point.}}, author = {{Larramendi, E M and Berth, Gerhard and Wiedemeier, V and Hüsch, K-P and Zrenner, Artur and Woggon, U and Tschumak, E and Lischka, K and Schikora, D}}, issn = {{0268-1242}}, journal = {{Semiconductor Science and Technology}}, number = {{7}}, publisher = {{IOP Publishing}}, title = {{{Intensity enhancement of Te Raman modes by laser damage in ZnTe epilayers}}}, doi = {{10.1088/0268-1242/25/7/075003}}, volume = {{25}}, year = {{2010}}, } @article{4550, abstract = {{We have integrated individual (In,Ga)As quantum dots (QDs) using site-controlled molecular beam epitaxial growth into the intrinsic region of a p-i-n junction diode. This is achieved using an in situ combination of focused ion beam prepatterning, annealing, and overgrowth, resulting in arrays of individually electrically addressable (In,Ga)As QDs with full control on the lateral position. Using microelectroluminescence spectroscopy we demonstrate that these QDs have the same optical quality as optically pumped Stranski–Krastanov QDs with random nucleation located in proximity to a doped interface. The results suggest that this technique is scalable and highly interesting for different applications in quantum devices.}}, author = {{Mehta, M. and Reuter, Dirk and Wieck, A. D. and Michaelis de Vasconcellos, S. and Zrenner, Artur and Meier, Cedrik}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, number = {{14}}, publisher = {{AIP Publishing}}, title = {{{An intentionally positioned (In,Ga)As quantum dot in a micron sized light emitting diode}}}, doi = {{10.1063/1.3488812}}, volume = {{97}}, year = {{2010}}, }