A. Zrenner

Universität Paderborn, Paderborn, North Rhine-Westphalia, Germany

Are you A. Zrenner?

Claim your profile

Publications (170)437.04 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Confocal Raman spectroscopy is applied to identify ferroelectric domain structure sensitive phonon modes in potassium titanyl phosphate. Therefore, polarization-dependent measurements in various scattering configurations have been performed to characterize the fundamental Raman spectra of the material. The obtained spectra are discussed qualitatively based on an internal mode assignment. In the main part of this work, we have characterized z-cut periodically poled potassium titanyl phosphate in terms of polarity- and structure-sensitive phonon modes. Here, we find vibrations whose intensities are linked to the ferroelectric domain walls. We interpret this in terms of changes in the polarizability originating from strain induced by domain boundaries and the inner field distribution. Hence, a direct and 3D visualization of ferroelectric domain structures becomes possible in potassium titanyl phosphate.
    No preview · Article · Jan 2016 · Journal of Applied Physics
  • M. Rüsing · T. Wecker · G. Berth · D. J. As · A. Zrenner
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstractauthoren Cubic gallium nitride (GaN) films are analyzed with high-resolution X-ray diffraction (HRXRD) and Raman spectroscopy. Several cubic GaN layers were grown on 3C-SiC (001) substrate by radio-frequency plasma-assisted molecular beam epitaxy. The layer thickness of the cubic GaN was varied between 75 and 505 nm. The HRXRD analysis reveals a reduction of the full-width at half-maximum (FWHM) of omega scans for growing layer thicknesses, which is caused by a partial compensation of defects. The Raman characterization confirms well-formed c-GaN layers. A more detailed examination of the longitudinal optical mode hints at a correlation of the FWHM of the Raman mode with the dislocation density, which shows the possibility to determine dislocation densities by Raman spectroscopy on a micrometer scale, which is not possible by HRXRD. Furthermore, this Raman analysis shows that normalized Raman spectra present an alternative way to determine layer thicknesses of thin GaN films.
    No preview · Article · Jan 2016 · physica status solidi (b)
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Spins in semiconductor quantum dots have been considered as prospective quantum bit excitations. Their coupling to the crystal environment manifests itself in a limitation of the spin coherence times to the microsecond range, both for electron and hole spins. This rather short-lived coherence compared to atomic states asks for manipulations on timescales as short as possible. Due to the huge dipole moment for transitions between the valence and conduction band, pulsed laser systems offer the possibility to perform manipulations within picoseconds or even faster. Here, we report on results that show the potential of optical spin manipulations with currently available pulsed laser systems. Using picosecond laser pulses, we demonstrate optically induced spin rotations of electron and hole spins. We further realize the optical decoupling of the hole spins from the nuclear surrounding at the nanosecond timescales and demonstrate an all-optical spin tomography for interacting electron spin sub-ensembles.
    Full-text · Article · Jan 2016 · Applied Physics B
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We analyse an InAs/GaAs-based electric field tunable single quantum dot diode with a thin tunnelling barrier between a buried n+-back contact and a quantum dot layer. In voltage-dependent photoluminescence measurements, we observe rich signatures from spatially direct and indirect transitions from the wetting layer and from a single quantum dot. By analysing the Stark effect, we show that the indirect transitions result from a recombination between confined holes in the wetting or quantum dot layer with electrons from the edge of the Fermi sea in the back contact. Using a 17nm tunnel barrier which provides comparably weak tunnel coupling allowed us to observe clear signatures of direct and corresponding indirect lines for a series of neutral and positively charged quantum dot states.
    Full-text · Article · Nov 2015
  • Source
    Dirk Heinze · Artur Zrenner · Stefan Schumacher
    [Show abstract] [Hide abstract]
    ABSTRACT: Sources of single photons are key elements in the study of basic quantum optical concepts and applications in quantum information science. Among the different sources available, semiconductor quantum dots excel with their straight forward integrability in semiconductor based on-chip solutions and the potential that photon emission can be triggered on demand. Usually, the photon emission event is part of a cascaded biexciton-exciton emission scheme. Important properties of the emitted photon such as polarization and time of emission are either probabilistic in nature or pre-determined by electronic properties of the system. In this work, we study the direct two-photon emission from the biexciton. We show that emission through this higher-order transition provides a much more versatile approach to generate a single photon. In the scheme we propose, the two-photon emission from the biexciton is enabled by a laser field (or laser pulse) driving the system into a virtual state inside the band gap. From this intermediate virtual state, the single photon of interest is then spontaneously emitted. Its properties are determined by the driving laser pulse, enabling all-optical on-the-fly control of polarization state, frequency, and time of emission of the photon.
    Full-text · Article · Oct 2015 · Nature Communications
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: LiTaO3 and LiNbO3 crystals are investigated here in a combined experimental and theoretical study that uses Raman spectroscopy in a complete set of scattering geometries and corresponding density-functional theory calculations to provide microscopic information on their vibrational properties. The Raman scattering efficiency is computed from first principles in order to univocally assign the measured Raman peaks to the calculated eigenvectors. Measured and calculated Raman spectra are shown to be in qualitative agreement and confirm the mode assignment by Margueron et al. [J. Appl. Phys. 111, 104105 (2012)], thus finally settling a long debate. While the two crystals show rather similar vibrational properties overall, the E-TO9 mode is markedly different in the two oxides. The deviations are explained by a different anion-cation bond type in LiTaO3 and LiNbO3 crystals.
    Full-text · Article · Jun 2015 · Physical Review B
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The coherent state preparation and control of single quantum systems is an important prerequisite for the implementation of functional quantum devices. Prominent examples for such systems are semiconductor quantum dots, which exhibit a fine structure split single exciton state and a V-type three level structure, given by a common ground state and two distinguishable and separately excitable transitions. In this work we introduce a novel concept for the preparation of a robust inversion by the sequential excitation in a V-type system via distinguishable paths.
    Full-text · Article · May 2015 · Scientific Reports
  • [Show abstract] [Hide abstract]
    ABSTRACT: 500 MHz surface acoustic waves travel across a commensurate plasmonic grating coupler. A stroboscopic optical technique shows that the dynamic surface deformation deliberately modulates the coupler's efficiency by +/-2\% during the ~2ns acoustic cycle
    No preview · Conference Paper · Jun 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: We explore the impact of 500 MHz surface acoustic waves traveling across a commensurable plasmonic grating coupler. A stroboscopic technique involving surface acoustic waves synchronized to a modelocked optical source allows to time-resolve the dynamical impact of the electromechanically induced perturbation. The surface acoustic wave periodically enhances or decreases the surface ripple of the static grating. Most remarkably, the dynamic surface deformation deliberately modulates the coupler’s efficiency by ±2% during the 2 ns acoustic cycle.
    No preview · Article · Feb 2014
  • Stefan Schumacher · Artur Zrenner
    [Show abstract] [Hide abstract]
    ABSTRACT: Emitters based on semiconductor quantum dots are promising sources for both single photons and pairs of polarization-entangled photons. Typically, single photons are generated through a photon emission event bringing the electronic system from a single-exciton state back to the ground state. In the case of entangled photons two photons are generated through a cascaded emission from the biexciton to either one of the single-exciton states and then back to the ground state. Alternatively, emission of two photons can also be achieved through a higher-order two-photon process bringing the quantum dot directly from the biexciton state (through a virtual intermediate state) back to the ground state. Here we discuss in particular how this two-photon process can lead to certain conceptual advantages in both the generation of polarization-entangled photon pairs and generation of single photons.
    No preview · Article · Mar 2013 · Proceedings of SPIE - The International Society for Optical Engineering
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jan 2013 · Ferroelectrics
  • [Show abstract] [Hide abstract]
    ABSTRACT: Coherent physics and applications of exciton qubits in electric field 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 field 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 field of coherent optoelectronics.
    No preview · Chapter · Jul 2012
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jun 2012 · Optics Express
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Feb 2012 · Optics Express
  • [Show abstract] [Hide abstract]
    ABSTRACT: The existence of localized vibrational modes both at the positive and at the negative LiNbO<sub>3</sub> (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 LiNbO<sub>3</sub> 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.
    No preview · Article · Oct 2011 · IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control
  • S. Declair · T. Meier · A. Zrenner · J. Förstner
    [Show abstract] [Hide abstract]
    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.Highlights► Numerical study of strongly interacting planar photonic crystal cavities. ► Optimization of Q factor to 43,000 for single cavity. ► For two pair of cavities strongest coupling is found for an angle of 30°. ► For three cavities a linear arrangement is optimal.
    No preview · Article · Oct 2011 · Photonics and Nanostructures - Fundamentals and Applications
  • [Show abstract] [Hide abstract]
    ABSTRACT: Uniform mesoporous Si double layers are formed on 4 inch p-type wafers with an off orientation of 6º towards 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 0.55nm for the unprocessed wafers to 0.27nm after etching and 0.78nm 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.
    No preview · Article · Oct 2011 · Thin Solid Films
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Sep 2011 · Semiconductor Science and Technology
  • [Show abstract] [Hide abstract]
    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.
    No preview · Conference Paper · Sep 2011
  • Source
    [Show abstract] [Hide abstract]
    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. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Full-text · Article · Apr 2011 · physica status solidi (c)

Publication Stats

4k Citations
437.04 Total Impact Points

Institutions

  • 2001-2015
    • Universität Paderborn
      • Department of Physics
      Paderborn, North Rhine-Westphalia, Germany
  • 1985-2007
    • Technische Universität München
      • • Walter Schottky Institut (WSI)
      • • Faculty of Physics
      München, Bavaria, Germany
  • 1989-1990
    • Princeton University
      • Department of Electrical Engineering
      Princeton, New Jersey, United States
  • 1988
    • Deutsches Herzzentrum München
      München, Bavaria, Germany