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Lehrstuhl Halbleiteroptik

Quantum-Dot Single-Photon Sources for Entanglement Enhanced Interferometry

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Multiphoton entangled states such as “N00N states” have attracted a lot of attention because of their possible application in high-precision, quantum enhanced phase determination. So far, N00N states have been generated in spontaneous parametric down-conversion processes and by mixing quantum and classical light on a beam splitter. Here, in contrast, we demonstrate superresolving phase measurements based on two-photon N00N states generated by quantum dot single-photon sources making use of the Hong-Ou-Mandel effect on a beam splitter. By means of pulsed resonance fluorescence of a charged exciton state, we achieve, in postselection, a quantum enhanced improvement of the precision in phase uncertainty, higher than prescribed by the standard quantum limit. An analytical description of the measurement scheme is provided, reflecting requirements, capability, and restraints of single-photon emitters in optical quantum metrology. Our results point toward the realization of a real-world quantum sensor in the near future.

Publication: Quantum-Dot Single-Photon Sources for Entanglement Enhanced Interferometry
M. Müller, H. Vural, C. Schneider, A. Rastelli, O.G. Schmidt, S. Höfling, and P. Michler
externer Link Phys. Rev. Lett. 118, 257402 (2017)

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Contact person: M.Müller

Quantum Dots for Quantum Information Technologies

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This book highlights the most recent developments in quantum dot spin physics and the generation of deterministic superior non-classical light states with quantum dots. In particular, it addresses single quantum dot spin manipulation, spin-photon entanglement and the generation of single-photon and entangled photon pair states with nearly ideal properties. The role of semiconductor microcavities, nanophotonic interfaces as well as quantum photonic integrated circuits is emphasized. The latest theoretical and experimental studies of phonon-dressed light matter interaction, single-dot lasing and resonance fluorescence in QD cavity systems are also provided. The book is written by the leading experts in the field.

Publication: Quantum Dots for Quantum Information Technologies
P. Michler (Ed) (invited)
externer Link Nanooptics and Nanophotonics
(Springer, Berlin, Heidelberg 2017)


Contact person: Prof. Dr. Michler

Semiconductor membrane external-cavity surface-emitting laser (MECSEL)

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Optically pumped semiconductor disk lasers are an important class of solid state lasers. Despite all their advantages, however, they suffer from heat incorporation into the active region caused by the excess energy of the pump photons. To overcome the limits of common methods in thermal management, we realized in a joint collaboration between the IHFG and the IFSW the semiconductor membrane external-cavity surface-emitting laser (MECSEL) consisting of a diamond heat spreader sandwiched active region design without a monolithically integrated distributed Bragg reflector (DBR). This diamond-sandwich approach improves the heat dissipation out of the active region and makes generally low-heat conductive DBRs obsolete. In an AlGaInP-based system, we demonstrate 595 mW output power at a wavelength of 657 nm and heatsink temperature of 10°C. The MECSEL enables a variety of new material combinations for new laser wavelengths and further potential for power scaling.

Publication: Semiconductor membrane external-cavity surface-emitting laser (MECSEL)
Hermann Kahle, Cherry May N. Mateo, Uwe Brauch, Philipp Tatar-Mathes, Roman Bek, Michael Jetter, Thomas Graf, and Peter Michler
externer Link Optica 3(12), 1506-1512 (2016)

Press releases

Pressemitteilung Uni Stuttgart

Photonic.de

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photonics.com

Contact person: Dr. M. Jetter

Simultaneous Faraday filtering of the Mollow triplet sidebands with the Cs-D1 clock transition

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The present work arises from a joint collaboration between the IHFG, the 3rd Institute of Physics and the Max Planck institute for solid state research. The final scope was the quantum hybrid interface between high quality single photons from a semiconductor quantum dot and efficient filters based on alkali atomic vapors. Cs atoms have been used to realize a so-called “Faraday anomalous dispersion optical filter” (FADOF) which is very well known and largely used by the atomic physics community. This filter, based on the Faraday effect, has been utilized as high performance two-color filter. Single photons coming from the Mollow triplet were generated via a strong continuous-wave resonant pumping and sent throughout the FADOF. Only the photons interacting with the atomic vapors can be transmitted while all other wavelengths undergo a strong rejection. Due to the intrinsic tunability of the Mollow triplet spectrum, the photons coming from the sidebands where tuned in resonance with the atomic transitions and therefore simultaneously transmitted, while the central Rayleigh line together with the unwanted laser scattering were largely suppressed. This work appears to be of high interest for the implementation of quantum networks.

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Opli, the magazine of Electro – Optics, Imaging and Machine Vision, Medical engineering, Photonics, Physics, and Solar Energy.

http://www.opli.net/opli_magazine/eo/2016/integrating-quantum-dots-and-atomic-vapors-nov-news/
 

Publication: Simultaneous Faraday filtering of the Mollow triplet sidebands with the Cs-D1 clock transition
Simone Luca Portalupi, Matthias Widmann, Cornelius Nawrath, Michael Jetter, Peter Michler, Jörg Wrachtrup, Ilja Gerhardt
externer Link Nature Communications 7, 13632 (2016)


Contact person:
Dr. Simone Luca Portalupi

Low-noise quantum frequency down-conversion of indistinguishable photons

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We present experimental results on quantum frequency down-conversion of indistinguishable single photons emitted by an InAs/GaAs quantum dot at 904 nm to the telecom C-band at 1557 nm. Hong-Ou-Mandel (HOM)interference measurements are shown prior to, and after the down-conversion step. We perform Monte Carlo simulations of the HOM experiments taking into account the time delays of the different interferometers used and the signal-to-background ratio and further estimate the impact of spectral diffusion on the degree of indistinguishability. By that we conclude that the down-conversion step does not introduce any loss of HOM interference visibility. A noise-free conversion-process along with a high conversion-efficiency (> 30%)emphasize that our scheme is a promising candidate for an efficient source of indistinguishable single photons at telecom wavelengths.

 

Publication: Low-noise quantum frequency down-conversion of indistinguishable photons
Benjamin Kambs, Jan Kettler, Matthias Bock , Jonas Nils Becker, Carsten Arend, Andreas Lenhard, Simone Luca Portalupi, Michael Jetter, Peter Michler, Christoph Becher
externer Link Opt. Express 24, 22250 (2016)


Contact person:
Jonas Weber

Neutral and charged biexciton-exciton cascade in near-telecom-wavelength quantum dots

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We investigate the cascaded emission of photons from low-density InGaAs/GaAs quantum dots grown by metal-organic vapor-phase epitaxy that are intentionally redshifted towards telecommunication wavelengths. We observe multiple radiative cascades within a single quantum dot and attribute these to neutral and charged excited configurations. The corresponding transitions are identified by combining microphotoluminescence and photon correlation measurements. Full-configuration interaction calculations further support the identification of the emission lines and provide additional information about the confinement of electron and hole wave functions. We apply a Monte Carlo simulation to estimate the effective spin scattering rates between excited triplet and singlet ground states of the negatively charged trion. These spin-flip processes directly affect the observed radiative cascade.

 

Publication: Neutral and charged biexciton-exciton cascade in near-telecom-wavelength quantum dot
Jan Kettler, Matthias Paul, Fabian Olbrich, Katharina Zeuner, Michael Jetter, Peter Michler, Matthias Florian, Christian Carmesin, Frank Jahnke
externer Link Phys. Rev. B 94, 045303 (2016)


Contact person:
Fabian Olbrich

Cavity-enhanced simultaneous dressing of quantum dot exciton and biexciton states

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We demonstrate the simultaneous dressing of both vacuum-to-exciton and exciton-to-biexciton transitions of a single semiconductor quantum dot in a high-Q micropillar cavity, using photoluminescence spectroscopy. Resonant two-photon excitation of the biexciton is achieved by spectrally tuning the quantum dot emission with respect to the cavity mode. The cavity couples to both transitions and amplifies the Rabi frequency of the likewise resonant continuous wave laser, driving the transitions. We observe strong-field splitting of the emission lines, which depend on the driving Rabi field amplitude and the cavity-laser detuning. A dressed state theory of a driven 4-level atom correctly predicts the distinct spectral transitions observed in the emission spectrum, and a detailed description of the emission spectra is further provided through a polaron master equation approach which accounts for cavity coupling and acoustic phonon interactions of the semiconductor medium.

 

Publication: Cavity-enhanced simultaneous dressing of quantum dot exciton and biexciton states
F. Hargart, M. Müller, K. Roy-Choudhury, S. L. Portalupi, C. Schneider, S. Höfling, M. Kamp, S. Hughes, and P. Michler
externer Link Phys. Rev. B 93, 115308 (2016)


Contact person:
Simon Seyfferle

Generation, guiding and splitting of triggered single photons from a resonantly excited quantum dot in a photonic circuit

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We demonstrate resonance fluorescence from single InGaAs/GaAs quantum dots embedded in a rib waveguide beamsplitter structure operated under pulsed laser excitation. A systematic study on the excitation laser pulse duration depicts that a sufficiently small laser linewidth enables a substantial improved single-photon-to-laser-background ratio inside a waveguide chip. This manifests in the observation of clear Rabi oscillations over two periods of the quantum dot emission as a function of laser excitation power. A photon cross-correlation measurement between the two output arms of an on-chip beamsplitter results in a g (2)(0)= 0.18, demonstrating the generation, guiding and splitting of triggered single photons under resonant excitation in an on-chip device. The present results open new perspectives for the implementation of photonic quantum circuits with integrated quantum dots as resonantly-pumped deterministic single-photon sources.

 

Publication: Generation, guiding and splitting of triggered single photons from a resonantly excited quantum dot in a photonic circuit
Mario Schwartz, Ulrich Rengstl, Thomas Herzog, Matthias Paul, Jan Kettler, Simone Luca Portalupi, Michael Jetter, and Peter Michler
externer Link Optics Express Vol. 24, Issue 3, pp. 3089-3094 (2016)


Contact person:
Mario Schwartz

Sichere Kommunikation per Quantenrepeater

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Die einzige, physikalisch garantiert abhörsichere Kommunikationstechnik basiert auf dem Austausch von Quantenschlüsseln. Allerdings endet ihre Reichweite in Glasfasernetzen bei etwa 100 km. Quantenrepeater sollen diese Grenze durch geschicktes Kombinieren von elementaren Quantenoperationen überwinden. Das Grundkonzept ist klar, doch die technische Realisierung eine große Herausforderung.

 

Publication: Sichere Kommunikation per Quantenrepeater
Christoph Becher, Dieter Meschede, Peter Michler, Reinhard Werner
externer Link Physik in unserer Zeit 1, 2016(47)


Contact person:
Prof. Peter Michler

Photonische Schaltkreise mit Einzelphotonenquellen

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Die zukünftige Anwendung von linearer Optik für die Quanteninformationsverarbeitung hängt stark von der Miniaturisierung der verwendeten optischen Elemente ab. Während heutige Versuche zur Quantenkryptographie und Quanteninformatik meist ganze Labortische füllen, arbeiten mehrere Forschungsinstitute an der Integration der benötigten optischen Bauteile auf einzelne Halbleiterchips.

 

Publication: Photonische Schaltkreise mit Einzelphotonenquellen
Ulrich Rengst, Mario Schwarz, Michael Jetter und Peter Michler
externer Link Photonik6, 58(2015)


Contact person:
Ulrich Rengstl

Intra-cavity frequency-doubled mode-locked semiconductor disk laser at 325 nm

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We present a passively mode-locked semiconductor disk laser (SDL) emitting at 650nm with intra-cavity second harmonic generation to the ultraviolet (UV) spectral range. Both the gain and the absorber structure contain InP quantum dots (QDs) as active material. In a v-shaped cavity using the semiconductor samples as end mirrors, a beta barium borate (BBO) crystal is placed in front of the semiconductor saturable absorber mirror (SESAM) for pulsed UV laser emission in one of the two outcoupled beams. Autocorrelation (AC) measurements at the fundamental wavelength reveal a FWHM pulse duration of 1.22ps. With a repetition frequency of 836MHz, the average output power is 10mW per beam for the red emission and 0.5mW at 325nm.

 

Publication: Intra-cavity frequency-doubled mode-locked semiconductor disk laser at 325 nm
Roman Bek, Stefan Baumgärtner, Fabian Sauter, Hermann Kahle, Thomas Schwarzbäck, Michael Jetter, and Peter Michler
externer Link Opt. Express 23(15), 19947-19953 (2015)


Contact person:
Roman Bek

On-chip beamsplitter operation on single photons from quasi-resonantly excited quantum dots embedded in GaAs rib waveguides

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We present an on-chip beamsplitter operating on a single-photon level by means of a quasi-resonantly driven InGaAs/GaAs quantum dot. The single photons are guided by rib waveguides and split into two arms by an evanescent field coupler. Although the waveguides themselves support the fundamental TE and TM modes, the measured degree of polarization (~90%) reveals the main excitation and propagation of the TE mode. We observe the preserved single-photon nature of a quasi-resonantly excited quantum dot by performing a cross-correlation measurement on the two output arms of the beamsplitter. Additionally, the same quantum dot is investigated under resonant excitation, where the same splitting ratio is observed. An autocorrelation measurement with an off-chip beamsplitter on a single output arm reveal the single-photon nature after evanescent coupling inside the on-chip splitter. Due to their robustness, adjustable splitting ratio, and their easy implementation, rib waveguide beamsplitters with embedded quantum dots provide a promising step towards fully integrated quantum circuits.

 

Publication: On-chip beamsplitter operation on single photons from quasi-resonantly excited quantum dots embedded in GaAs rib waveguides
U Rengstl, M Schwartz, T Herzog, F Hargart, M Paul, S Portalupi, M Jetter and P Michler
externer Link Appl. Phys. Lett. 107, 021101 (2015)


Contact person:
Ulrich Rengstl

Fabrication and optical characterization of large scale membrane containing InP/ AlGaInP quantum dots

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Single-photon sources with a high extraction efficiency are a prerequisite for applications in quantum communication and quantum computation schemes. One promising approach is the fabrication of a quantum dot containing membrane structure in combination with a solid immersion lens and a metal mirror. We have fabricated an 80 nm thin semiconductor membrane with incorporated InP quantum dots in an AlGaInP double hetero barrier via complete substrate removal. In addition, a gold layer was deposited on one side of the membrane acting as a mirror. The optical characterization shows in detail that the unique properties of the quantum dots are preserved in the membrane structure.

 

Publication: Fabrication and optical characterization of large scale membrane containing InP/ AlGaInP quantum dots
H Niederbracht, F Hargart, M Schwartz, E Koroknay, C A Kessler, M Jetter and P Michler
externer Link Nanotechnology 26 (2015) 235201


Contact person:
Dr. M. Jetter

Phonon-assisted robust and deterministic two-photon biexciton preparation in a quantum dot

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We investigate both experimentally and theoretically a simple yet more robust and flexible alternative to Rabi oscillation-type biexciton preparation protocols traditionally used for semiconductor quantum dots. The quantum dot is excited by a strong laser pulse positively detuned from the two-photon resonance yielding an on demand initialization of the biexciton state by making use of the phonon-induced thermalization of the photon dressed states. It is shown that for excitation pulses in the picosecond range, a stable and high occupation of up to C_XX=0.95±0.02 is reached. Notably, the generated photons show similar coherence properties as measured in the resonant two-photon scheme. This protocol is a powerful tool for the control of complex solid state systems combining radiative cascades, entanglement, and resonant cavity modes..

 

Publication: Phonon-assisted robust and deterministic two-photon biexciton preparation in a quantum dot
S. Bounouar, M. Müller, A. M. Barth, M. Glässl, V. M. Axt, and P. Michler
externer Link Publication: Phys. Rev. B 91, 161302 (2015)


Contact person:
Markus Müller

Metal-organic vapor-phase epitaxy-grown ultra-low density InGaAs/GaAs quantum dots exhibiting cascaded single-photon emission at 1.3 µm

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Semiconductor quantum dots (QDs) have attracted persistent attention due to their plethora of possible applications including, not at last, the generation of cascaded and entangled photon pairs. The concept of entanglement can be utilized in quantum cryptography schemes or quantum repeaters, where solid-state based non-classical light sources constitute a feasible straightforward device implementation due to their high integrability. InGaAs QDs embedded in a GaAs matrix play an important role in that regard offering high extraction efficiencies through photonic cavities and site-controlled growth. Besides the generation of entanglement, not only the generation of indistinguishable photons has been shown but also the QDs’ emission wavelengths can be tuned over a wide spectral range. Communication networks on the basis of glass fiber technology mainly rely on transmission in the telecom wavelength bands at 1.31 µm (O-band) and 1.55 µm (C-band), corresponding to the dispersion and absorption minima. By applying an InGaAs strain reducing layer (SRL), the emission wavelengths of InGaAs QDs can be precisely shifted to the telecom O-band.

By metal-organic vapor-phase epitaxy, we have fabricated InGaAs quantum dots on GaAs substrate with an ultra-low lateral density (<10 7 cm 2). The photoluminescence emission from the quantum dots is shifted to the telecom O-band at 1.31 µm by an InGaAs strain reducing layer. In time-resolved measurements, we find fast decay times for exciton (600 ps) and biexciton (300 ps). We demonstrate triggered single-photon emission (g (2)(0)= 0.08) as well as cascaded emission from the biexciton decay. Our results suggest that these quantum dots can compete with their counterparts grown by state-of-the-art molecular beam epitaxy.

 

Publication: Metal-organic vapor-phase epitaxy-grown ultra-low density InGaAs/GaAs quantum dots exhibiting cascaded single-photon emission at 1.3 µm
Matthias Paul, Jan Kettler, Katharina Zeuner, Caterina Clausen, Michael Jetter and Peter Michler
externer Link Publication: Appl. Phys. Lett. 106, 122105 (2015)


Contact person:
Stefan Hepp

Monolithic on-chip integration of semiconductor waveguides, beamsplitters and single-photon sources

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The implementation of fully integrated single-photon sources and detectors into waveguide structures such as photonic crystals or a slab and ridge waveguide is currently one of the major goals in the linear optics quantum computation and communication community. Here, we present an implementation of a single-photon on-chip experiment based on a III–V semiconductor platform. Individual semiconductor quantum dots were used as pulsed single-photon sources integrated in ridge waveguides, and the on-chip waveguide-beamsplitter operation is verified on the single-photon level by performing off-chip photon cross-correlation measurements between the two output ports of the beamsplitter. A degree of polarization of the emitted photons above 90% is observed and a careful characterization of the waveguide propagation losses in straight (< 1.5 dB mm -1) and bent (~ (8.5 ± 2.2) dB mm -1) sections documents the applicability of such GaAs-based waveguide structures in more complex photonic integrated circuits. The presented work marks an important step towards the realization of fully integrated photonic quantum circuits including on-demand single-photon emitters.

 

Publication: Monolithic on-chip integration of semiconductor waveguides, beamsplitters and single-photon sources
Klaus D Jöns, Ulrich Rengstl, Markus Oster, Fabian Hargart, Matthias Heldmaier, Samir Bounouar, Sven M Ulrich, Michael Jetter and Peter Michler
externer Link J. Phys. D: Appl. Phys. 48 085101


Contact person:
Ulrich Rengstl

Spectroscopy of the D1 transition of cesium by dressed-state resonance fluorescence from a single (In,Ga)As/GaAs quantum dot

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We use a laser-driven single (In,Ga)As quantum dot (QD) in the dressed-state regime of resonance fluorescence (T=4K) to observe the four D1-transition lines of alkali atomic cesium (Cs) vapor at room temperature. We tune the frequency of the dressing continuous-wave laser in the vicinity of the bare QD resonance ∼335.116THz (∼894.592nm) at constant excitation power and thereby controllably tune the center and side channel frequencies of the probe light, i.e., the Mollow triplet. Resonances between individual QD Mollow triplet lines and the atomic hyperfine-split transitions are clearly identified in the Cs absorption spectrum. Our results show that narrow-band (In,Ga)As QD resonance fluorescence (RF) is suitable to optically address individual transitions of the D1 quadruplet without applying magnetic field or electric field tuning.

 

Publication: Spectroscopy of the D1 transition of cesium by dressed-state resonance fluorescence from a single (In,Ga)As/GaAs quantum dot
S. M. Ulrich, S. Weiler, M. Oster, M. Jetter, A. Urvoy, R. Löw, and P. Michler
externer Link Phys. Rev. B 90, 125310 – Published 18 September 2014


Contact person:
Prof. Dr. P. Michler

On-demand generation of indistinguishable polarization-entangled photon pairs

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An on-demand source of indistinguishable and entangled photon pairs is a fundamental component of various quantum information applications, including optical quantum computing, quantum repeaters, quantum teleportation and quantum communication. Parametric downconversion and four-wave mixing sources of entangled photons have shown high degrees of entanglement and indistinguishability, but the probabilistic nature of their generation process also creates zero or multiple photon pairs following a Poissonian distribution. This limits their use in complex algorithms where many qubits and gate operations are required. Here, we simultaneously show ultrahigh purity (g (2)(0) < 0.004), high entanglement fidelity (0.81 ± 0.02), high two-photon interference non-post selective visibilities (0.86 ± 0.03 and 0.71 ± 0.04) and on-demand generation (efficiency ε pair = 0.86 ± 0.08) of polarization-entangled photon pairs from a single semiconductor quantum dot. Through a two-photon resonant excitation scheme, the biexciton population is deterministically prepared by a π-pulse (ε biexciton = 0.98 ± 0.07). Applied on a quantum dot showing no exciton fine-structure splitting, this results in the deterministic generation of indistinguishable entangled photon pairs.

 

Publication: On-demand generation of indistinguishable polarization-entangled photon pairs
M. Müller, S. Bounouar, K. D. Jöns, M. Glässl and P. Michler
externer Link Nature Photonics 8, 224-228 (2014)

News and Views article in Nature Photonics

Contact person:
Markus Müller

Mode-locked red-emitting semiconductor disk laser with sub-250 fs pulses

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We report on passive mode locking of a semiconductor disk laser emitting pulses shorter than 250 fs at 664 nm with a repetition frequency of 836 MHz. A fast saturable absorber mirror fabricated by metal-organic vapor-phase epitaxy in a near-resonant design was used to enable the mode locking operation. It includes two GaInP quantum wells located close to the surface and an additional fused silica coating. The emission spectrum shows the superposition of a soliton-like part and a smaller "continuum" part.

Publication: Mode-locked red-emitting semiconductor disk laser with sub-250 fs pulses
R. Bek, H. Kahle, T. Schwarzbäck, M. Jetter, and P. Michler
externer Link Applied Physics Letters 103, 242101

Contact person: Roman Bek

Postselected indistinguishable single-photon emission from the Mollow triplet sidebands of a resonantly excited quantum dot

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Applying high-power continuous-wave resonant s-shell excitation to a single self-assembled InGaAs quantum dot, we demonstrate the generation of postselected single-indistinguishable photons from the Mollow triplet sidebands. A sophisticated spatial filtering technique based on a double Michelson interferometer enabled us to separate the spectrally close lying individual Mollow components and perform almost background-free two-photon interference measurements. Showing high consistency with the results of an independent determination of the emission coherence of ∼250±30 ps, our analysis reveals a close to ideal visibility contrast of up to 97%. Due to their easy spectral tunability and their distinct advantage of cascaded-photon emission between the individual Mollow sidebands, they resemble a versatile tool for quantum information applications.

 

Publication: Postselected indistinguishable single-photon emission from the Mollow triplet sidebands of a resonantly excited quantum dot
S. Weiler, D. Stojanovic, S. M. Ulrich, M. Jetter and P. Michler
externer Link Phys. Rev. B 87, 241302(R) (2013))

Contact person: Prof. Dr. Peter Michler

Mollow quintuplets from coherently excited quantum dots

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Charge-neutral excitons in semiconductor quantum dots (QDs) have a small finite energy separation caused by the anisotropic exchange splitting. Coherent excitation of neutral excitons will generally excite both exciton components, unless the excitation is parallel to one of the dipole axes. We present a polaron master equation model to describe two-exciton pumping using a coherent continuous wave pump field in the presence of a realistic anisotropic exchange splitting. We predict a five-peak incoherent spectrum, namely a Mollow quintuplet under general excitation conditions. We experimentally confirm such spectral quintuplets for In(Ga)As QDs and obtain very good agreement with theory.

 

Publication: Mollow quintuplets from coherently excited quantum dots
Rong-Chun Ge, S. Weiler, A. Ulhaq, S. M. Ulrich, M. Jetter, P. Michler, and S. Hughes
externer Link Optics Letters Vol. 38, Iss. 10, pp. 1691–1693 (2013)

Contact person: Prof. Dr. Peter Michler

High-power InP quantum dot based semiconductor disk laser exceeding 1.3 W

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We demonstrate an optically pumped semiconductor disk laser (OP-SDL) using InP quantum dots (QDs) as active material fabricated by metal-organic vapor-phase epitaxy. The QDs are grown within [(Al0.1Ga0.9)0.52In0.48]0.5P0.5 (abbr. Al0.1GaInP) barriers in order to achieve an emission wavelength around 655 nm. We present optical investigations of the active region showing typical QD behavior like blue shift with increasing excitation power and single emission lines, which show anti-bunching in an intensity auto-correlation measurement. We report maximum output powers of the OP-SDL of 1.39 W at low emission wavelength of ∼ 654 nm with a slope efficiency of ηdiff = 25.4 %.

Publication: High-power InP quantum dot based semiconductor disk laser exceeding 1.3 W
T. Schwarzbäck, R. Bek, F. Hargart, C. A. Kessler, H. Kahle, E. Koroknay, M. Jetter, and P. Michler
externer Link Applied Physics Letters 102, 092101

Contact person: Roman Bek

Detuning-dependent Mollow triplet of a coherently-driven single quantum dot

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We present both experimental and theoretical investigations of a laser-driven quantum dot (QD) in the dressed-state regime of resonance fluorescence. We explore the role of phonon scattering and pure dephasing on the detuning-dependence of the Mollow triplet and show that the triplet sidebands may spectrally broaden or narrow with increasing detuning. Based on a polaron master equation approach, which includes electron-phonon interaction nonperturbatively, we derive a fully analytical expression for the spectrum. With respect to detuning dependence, we identify a crossover between the regimes of spectral sideband narrowing or broadening. We also predict regimes of phonon-induced squeezing and anti-squeezing of the spectral resonances. A comparison of the theoretical predictions to detailed experimental studies on the laser detuning-dependence of Mollow triplet resonance emission from single In(Ga)As QDs reveals excellent agreement.

 

Publication: Detuning-dependent Mollow triplet of a coherently-driven single quantum dot
Ata Ulhaq, Stefanie Weiler, Chiranjeeb Roy, Sven Marcus Ulrich, Michael Jetter, Stephen Hughes, and Peter Michler
externer Link Optics Express Vol. 21, Iss. 4, pp. 4382–4395 (2013)

Contact person: Prof. Dr. Peter Michler

Strong mode coupling in InP quantum dot-based GaInP microdisk cavity dimers

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We report on strong mode coupling in closely spaced GaInP microdisk dimer structures including InP quantum dots as the active medium. Using electron beam lithography and a combination of dry- and wet-etch processes, dimers with inter-disk separations down to d < 100 nm have been fabricated. Applying a photo-thermal heating scheme, we overcome the spectral mode detuning due to the size mismatch between the two disks forming the dimer. We observe signatures of mode coupling in the corresponding photoluminescence spectra with coupling energiesof up to 0.66 MeV. With the aid of a numerical analysis, we specify the geometrical and physical factors of the microdisk dimer precisely, and reproduce its spectrum with good agreement.

 

Publication: Strong mode coupling in InP quantum dot-based GaInP microdisk cavity dimers
M Witzany, T-L Liu, J-B Shim, F Hargart, E Koroknay, W-M Schulz, M Jetter, E Hu, J Wiersig, and P Michler
externer Link New J. Phys. 15, 013060 (2013)

Contact person: Simon Seyfferle

Influence of the oxide aperture radius on the mode spectra of (Al,Ga)As vertical microcavities with electrically excited InP quantum dots

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We report about the mode characteristics of microcavity lasers with red-emitting InP quantum dots. The mode spectra and the quality factor of devices with different oxide aperture sizes are analyzed. The lateral mode confinement in the electrical devices is defined via oxide apertures. We found a good agreement between a simple analytical modeling of the mode structure and measurements, which allows to adjust the design of future devices. The quality factors show an analogous behavior as etched micropillars. The enhanced intensity of the higher order modes compared to the fundamental mode can be explained with the current density distribution within the device favoring higher order modes.

Publication: Influence of the oxide aperture radius on the mode spectra of (Al,Ga)As vertical microcavities with electrically excited InP quantum dots
S. Weidenfeld,W.-M. Schulz, C. A. Kessler, M. Reischle, M. Eichfelder, M. Wiesner, M. Jetter, and P. Michler
externer Link Applied Physics Letters 102, 011132 (2013)

Contact person: Mona Stadler

Strain compensation techniques for red AlGaInP-VECSELs: Performance comparison of epitaxial designs

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We present a strain-compensation design for non-resonantly pumped vertical external cavity surface-emitting lasers for emission in the red spectral range around 665 nm. Here, the VECSEL chip is based on a metal-organic vapor- phase epitaxy grown (Ga x In 1−x ) 0.5 P 0.5 /[(Al x Ga 1-x ) y In 1−y ] 0.5 P 0.5 multi-quantum- well structure with 20 compressively-strained quantum wells. By introducing tensile strained quaternary barriers and cladding layers in a 5 × 4 QW design, we could compensate for the compressive strain introduced by the quan- tum wells. Photoluminenscence measurements of structures with different numbers of quantum well packages reveal a more homogenous quantum well growth due to the strain-compensation technique. Furthermore, with the strain compensation technique, the output power could be increased over 30 % compared to our conventional structures.

Publication: Strain compensation techniques for red AlGaInP-VECSELs: Performance comparison of epitaxial designs
T. Schwarzbäck, H. Kahle, M. Jetter, and P. Michler
externer Link Journal of Crystal Growth 370, 208 (2013), DOI: 10.1016/j.jcrysgro.2012.09.051

Contact person: Roman Bek

Electrically driven quantum dot single-photon source at 2 GHz excitation repetition rate with ultra-low emission time jitter

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The influence of the bias voltage on emission properties of a red emitting InP/GaInP quantum dot based single-photon source was investigated. Under pulsed electrical excitation, we can influence the band bending of the p-i-n diode with the applied bias voltage and thus the charge carrier escape by quantum tunneling. This leads to control over the non-radiative decay channel and allows carrier escape times as low as 40 ps, effectively reducing the time jitter of the photon emission. We realized high excitation repetition rates of up to 2 GHz while autocorrelation measurements with g (2)(0)-values of 0.27 attest dominant single-photon emission.

 

Publication: Electrically driven quantum dot single-photon source at 2 GHz excitation repetition rate with ultra-low emission time jitter
F. Hargart, C. A. Kessler, T. Schwarzbäck, E. Koroknay, S. Weidenfeld, M. Jetter, and P. Michler
externer Link Appl. Phys. Lett. 102, 011126 (2013)

Contact person: Simon Seyfferle

Site-controlled growth of InP/GaInP islands on periodic hole patterns in GaAs substrates produced by microsphere photolithography

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We have shown that microsphere photolithography in combination with wet chemical etching is a fast and low-cost method to produce regular hole arrays in a (100) GaAs surface, which are then suitable for controlled nucleation of self-organized InP islands in a metal-organic vapor-phase epitaxy (MOVPE) system. A hexagonally close-packed monolayer of microspheres is used as an array of microlenses to focus UV-light on UV-sensitive photoresist. In this way, regular arrays of holes with 2 µm spacing can be realized in the photoresist with controllable feature size in the sub-μm range, which are transferred to a GaAs buffer, using an isotropic etchant. These templates are used to study the site-controlled nucleation of InP islands on a Ga 0.51In 0.49P barrier. For this purpose the subsequent overgrowth of the templates with a GaAs buffer layer and the GaInP barrier is investigated previous to the additional deposition of the InP. The template quality is monitored during structuring and overgrowth experiments using atomic force microscopy (AFM). Preferred nucleation of InP islands inside the almost filled holes could be observed for uncapped samples. The correlation between the initial patterning and the optical signal of the InP islands is investigated by micro-photoluminescence (micro-PL) measurements. We observed site-controlled nucleation of large, but optically active, InP islands on these templates.

Publication: Site-controlled growth of InP/GaInP islands on periodic hole patterns in GaAs substrates produced by microsphere photolithography
E. Koroknay, U. Rengstl, M. Bommer, M. Jetter, P. Michler
externer Link Journal of Crystal Growth (2012) , DOI: 10.1016/j.jcrysgro.2012.09.058

Contact person: Marc Sartison

Phonon-assisted incoherent excitation of a quantum dot and its emission properties

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We present a detailed study of a phonon-assisted incoherent excitation mechanism of single quantum dots. A spectrally detuned continuous-wave laser couples to a quantum dot transition by mediation of acoustic phonons, whereby excitation efficiencies up to 20% with respect to strictly resonant excitation can be achieved at T=9 K. Laser-frequency-dependent analysis of the quantum dot intensity distinctly maps the underlying acoustic phonon bath and shows good agreement with our polaron master equation theory. An analytical solution for the steady-state exciton density (which is proportional to the photoluminescence) is introduced which predicts a broadband incoherent coupling process mediated by electron-phonon scattering. Moreover, we investigate the coherence properties of the emitted light with respect to strictly resonant versus phonon-assisted excitation, revealing the importance of narrow band triggered emitter-state initialization for possible applications of a quantum dot exciton system as a qubit.

 

Publication: Phonon-assisted incoherent excitation of a quantum dot and its emission properties
S. Weiler, A. Ulhaq, C. Roy, S.Hughes,S. M. Ulrich, D. Richter, M. Jetter, and P. Michler
externer Link Phys. Rev. B 86, 241304(R) (2012)

Contact person: Prof. Dr. Peter Michler

Triggered Indistinguishable Single Photons with Narrow Line Widths from Site-Controlled Quantum Dots

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In this Letter, we present narrow line width (7 μeV), nearly background-free single-photon emission (g (2)(0) = 0.02) and highly indistinguishable photons (V = 0.73) from site-controlled In(Ga)As/GaAs quantum dots. These excellent properties have been achieved by combining overgrowth on ex situ pit-patterned substrates with vertical stacking of spectrally distinct quantum dot layers. Our study paves the way for largescale integration of quantum dots into quantum photonic circuits as indistinguishable single-photon sources.

 

Publication: Triggered Indistinguishable Single Photons with Narrow Line Widths from Site-Controlled Quantum Dots
K. D. Jöns, P. Atkinson, M. Müller, M. Heldmaier, S. M. Ulrich, O. G. Schmidt, and P. Michler
externer Link Nano Lett., 2013, 13 (1), pp 126–130

Contact person: Prof. Dr. Peter Michler

Visible-to-Telecom Quantum Frequency Conversion of Light from a Single Quantum Emitter

Quelle:Andreas Lenhard, Universität des Saarlandes  (Hier klicken für eine größere Bildansicht) Quelle:Andreas Lenhard, Universität des Saarlandes

We demonstrate efficient (>30%) quantum frequency conversion of visible single photons (711 nm) emitted by a quantum dot to a telecom wavelength (1313 nm). Analysis of the first- and second-order coherence before and after wavelength conversion clearly proves that pivotal properties, such as the coherence time and photon antibunching, are fully conserved during the frequency translation process. Our findings underline the great potential of single photon sources on demand in combination with quantum frequency conversion as a promising technique that may pave the way for a number of new applications in quantum technology.

 

Publication: Visible-to-Telecom Quantum Frequency Conversion of Light from a Single Quantum Emitter
Sebastian Zaske, Andreas Lenhard, Christian A. Keßler, Jan Kettler, Christian Hepp, Carsten Arend, Roland Albrecht, Wolfgang-Michael Schulz, Michael Jetter, Peter Michler, and Christoph Becher
externer Link Phys. Rev. Lett. 109, 147404 (2012)
externer Link Synopsis
externer Link Pressemeldung Universität Stuttgart

Contact person: Prof. Dr. Peter Michler

Strong antibunching from electrically driven devices with long pulses: A regime for quantum-dot single-photon generation

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We present excitation-pulse-width- and pump-power-dependent microelectroluminescence and photon statistics measurements on electrically driven single-photon devices based on InP/AlGaInP quantum dots (QDs). For an excitation regime far below QD saturation, the results show a characteristic decrease of the purity of the single-photon emission [g(2)(0) value] with increasing excitation pulse width. For stronger excitation pulses close to QD saturation, strong antibunching is maintained for a much larger pulse width. In this case the ground-state exciton emission, which is used for the single-photon source, is inhibited during the pump pulse due to the presence of higher excited states. This prevents multiple-ground-state emission and reexcitation during long pump pulses and delays the single-photon emission to the end of the pulse, as predicted by theory and confirmed experimentally.

 

Publication: Strong antibunching from electrically driven devices with long pulses: A regime for quantum-dot single-photon generation
C. A. Kessler, M. Reischle, F. Hargart, W.-M. Schulz, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler P. Gartner, M. Florian, C. Gies, and F. Jahnke
externer Link Phys. Rev. B 86, 115326 (2012)

Contact person: Prof. Dr. Peter Michler

Quantum key distribution using quantum dot single-photon emitting diodes in the red and near infrared spectral range

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We report on in-lab free space quantum key distribution (QKD) experiments over 40 cm distance using highly efficient electrically driven quantum dot single-photon sources emitting in the red as well as near-infrared spectral range. In the case of infrared emitting devices, we achieve sifted key rates of 27.2 kbit s −1 (35.4 kbit s −1) at a quantum bit error rate (QBER) of 3.9% (3.8%) and a g (2)(0) value of 0.35 (0.49) at moderate (high) excitation. The red emitting diodes generate sifted keys at a rate of 95.0 kbit s −1 at a QBER of 4.1% and a g (2)(0) value of 0.49. This first successful proof of principle QKD experiment based on electrically operated semiconductor single-photon sources can be considered as a major step toward practical and efficient quantum cryptography scenarios.

 

Publication: Quantum key distribution using quantum dot single-photon emitting diodes in the red and near infrared spectral range
Tobias Heindel, Christian A Kessler, Markus Rau, Christian Schneider, Martin Fürst, Fabian Hargart, Wolfgang-Michael Schulz, Marcus Eichfelder, Robert Roßbach, Sebastian Nauerth, Matthias Lermer, Henning Weier, Michael Jetter, Martin Kamp, Stephan Reitzenstein, Sven Höfling, Peter Michler, Harald Weinfurter and Alfred Forchel
externer Link New J. Phys. 14, 083001 (2012))

Contact person: Prof. Dr. Peter Michler

Single-photon emission from electrically driven InP quantum dots epitaxially grown on CMOS-compatible Si(001)

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The heteroepitaxy of III–V semiconductors on silicon is a promising approach for making silicon a photonic platform. Mismatches in material properties, however, present a major challenge, leading to high defect densities in the epitaxial layers and adversely affecting radiative recombination processes. However, nanostructures, such as quantum dots, have been found to grow defect-free even in a suboptimal environment. Here we present the first realization of indium phosphide quantum dots on exactly oriented Si(001), grown by metal–o rganic vapour-phase epitaxy. We report electrically driven single-photon emission in the red spectral region, meeting the wavelength range of silicon avalanche photodiodes’ highest detection efficiency.

Publication: Single-photon emission from electrically driven InP quantum dots epitaxially grown on CMOS-compatible Si(001)
M. Wiesner, W-M. Schulz, C. Kessler, M. Reischle, S. Metzner, F. Bertram, J. Christen, R. Roßbach, M. Jetter and P. Michler
externer Link Nanotechnology 23, 335201 (2012)
externer Link Lab Talk

Contact person: Dr. M. Jetter

Epitaxially Grown Indium Phosphide Quantum Dots on a Virtual Ge Substrate Realized on Si(001)

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An ultrathin virtual Ge substrate (GeVS) with low defect density was realized on CMOS-compatible Si(001) by molecular beam epitaxy. On top, III–V layers were deposited by metal–organic vapor-phase epitaxy, at which diffusion of Ge was successfully suppressed. Nonclassical light emitters, based on InP quantum dots (QDs), were realized on a thin GaAs buffer (thickness ≈ 1 µm). The quantum dots show emission in the red spectral region, meeting the range of the highest detection efficiency of silicon avalanche photodiodes. The decay dynamics and emission characteristics of single QDs were investigated. Autocorrelation measurements prove single-photon emission with a value of g (2)(0)=0.32.

Publication: Epitaxially Grown Indium Phosphide Quantum Dots on a Virtual Ge Substrate Realized on Si(001)
Michael Wiesner, Moritz Bommer, Wolfgang-Michael Schulz, Martin Etter, Jens Werner, Michael Oehme, Jörg Schulze, Michael Jetter, and Peter Michler
externer Link Appl. Phys. Express 5, 042001 (2012)

Contact person: Dr. M. Jetter

Cascaded Single-Photon Emission from the Mollow Triplet Sidebands of a Quantum Dot

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Emission from a resonantly excited quantum emitter is a fascinating research topic within quantum optics and a useful source for different types of quantum light fields. The resonance spectrum consists of a single spectral line which develops into a triplet above saturation of the quantum emitter. The three closely-spaced photon channels from the resonance fluorescence (RF) have different photon statistical signatures. We present a detailed photon-statistics analysis of the RF emission triplet from a solid state-based artificial atom, i.e. a semiconductor quantum dot. The photon correlation measurements demonstrate both 'single' and 'cascaded' photon emission from the Mollow triplet sidebands. The bright and narrow sideband emission (5.9 million photons/second into the first lens) can be conveniently frequency-tuned by laser detuning over 15 times its linewidth (~ 1.0 GHz). These unique properties make the Mollow triplet sideband emission a valuable light source for, e.g. quantum light spectroscopy and quantum information applications.

 

Publication: Cascaded Single-Photon Emission from the Mollow Triplet Sidebands of a Quantum Dot
A. Ulhaq, S. Weiler, S. M. Ulrich, R. Roßbach, M. Jetter, and P. Michler
externer Link Nature Photonics 6, 238 - 242 (2012)

Contact person: Prof. Dr. Peter Michler

Wavelength tunable ultraviolet laser emission via intra-cavity frequency doubling of an AlGaInP vertical external-cavity surface-emitting laser down to 328 nm

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We demonstrate an optically pumped vertical external-cavity surface-emitting laser in a compact v-shaped cavity configuration for frequency doubling to the ultraviolet (UV) spectral range at ∼330 nm. The fundamental red laser emission is realized with a metal-organic vapor-phase epitaxy grown (Ga xIn 1−x) 0.5P 0.5/[(Al xGa 1−x) yIn 1−y] 0.5P 0.5 multi-quantum-well structure. Second harmonic generation is accomplished by using a beta barium borate non-linear crystal to generate maximum UV output powers exceeding 100 mW. By using a birefringent filter, we are able to tune the fundamental laser resonance to realize a maximum tuning range of 7.5 nm of the second harmonic.

Publication: Wavelength tunable ultraviolet laser emission via intra-cavity frequency doubling of an AlGaInP vertical external-cavity surface-emitting laser down to 328 nm
T. Schwarzbäck, H. Kahle, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler
externer Link Applied Physics Letters 99, 261101 (2011)

Contact person: Dr. M. Jetter

Halbleiterscheibenlaser für Spektroskopieanwendungen im roten und ultravioletten Spektralbereich

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Für die Spektroskopie im roten Spektralbereich sowie im UV stellen AlGaInP-Halbleiterscheibenlaser eine effiziente Ergänzung zu Titan:Saphir-Lasern dar. Die Verwendung eines externen Resonators ermöglicht eine hohe Ausgangsleistung im Dauerstrichbetrieb bei höchster Strahlqualität. Die offene Geometrie erlaubt im Gegensatz zu gewöhnlichen kanten- oder oberflächenemittierenden Halbleiterlasern eine breitbandige Wellenlängendurchstimmung und eine Frequenzverdopplung durch optische Elemente im Resonator. Wir präsentieren im Folgenden die Ergebnisse eines VECSEL-Entwicklungsprojekts.

Publication: Halbleiterscheibenlaser für Spektroskopieanwendungen im roten und ultravioletten Spektralbereich
Thomas Schwarzbäck, Hermann Kahle, Michael Jetter, Peter Michler
externer Link Photonik 6, 46-49 (2011) - www.photonik.de

Contact person: Dr. M. Jetter

Dependence of the Redshifted and Blueshifted Photoluminescence Spectra of Single InxGa1-xAs/GaAs Quantum Dots on the Applied Uniaxial Stress

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We apply external uniaxial stress to tailor the optical properties of In xGa 1-xAs/GaAs quantum dots. Unexpectedly, the emission energy of single quantum dots controllably shifts to both higher and lower energies under tensile strain. Theoretical calculations using a million atom empirical pseudopotential many-body method indicate that the shifting direction and magnitude depend on the lateral extension and more interestingly on the gallium content of the quantum dots. Our experimental results are in good agreement with the underlying theory.

Publication: Dependence of the Redshifted and Blueshifted Photoluminescence Spectra of Single
In xGa 1-xAs/GaAs Quantum Dots on the Applied Uniaxial Stress

K. D. Jöns, R. Hafenbrak, R. Singh, F. Ding, J. D. Plumhof, A. Rastelli, O. G. Schmidt, G. Bester, and P. Michler
externer Link Phys. Rev. Lett. 107, 217402 (2011)

Contact person: Prof. Dr. Peter Michler

Transverse-Mode Analysis of Red-Emitting Highly Polarized Vertical-Cavity Surface-Emitting Lasers

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We present experimental investigations of the transverse beam profile and polarization characteristics of GaInP-based oxide-confined vertical-cavity surface-emitting lasers in dependence on the oxide aperture size, mesa size, current, and temperature. We demonstrate that these lasers with aperture diameters of less than 6 µm are required for stable fundamental-mode operation. The influence of operation current and external temperature on the mode shape is investigated. We experimentally present a highly stable linearly polarized GaInP-based microcavity laser emitting at around 655 nm, where the polarization characteristics originate from intrinsic material properties.

Publication: Transverse-Mode Analysis of Red-Emitting Highly Polarized Vertical-Cavity Surface-Emitting Lasers
S. Weidenfeld, M. Eichfelder, M. Wiesner, W.-M. Schulz, R. Roßbach, M. Jetter, and P. Michler
externer Link IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 17, NO. 3, MAY/JUNE 2011

Contact person: Mona Stadler

Triggered single-photon emission in the red spectral range from optically excited InP/(Al,Ga)InP quantum dots embedded in micropillars up to 100 K

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Systematic excitation power and temperature-dependent measurements on the emission lines of single self-assembled InP/(Al 0.20Ga 0.80) 0.51In 0.49P quantum dots embedded in micropillars have been performed. The quantum dots were excited optically via a pulsed laser and their luminescence was collected using a micro-photoluminescence setup. The exciton and biexciton intensity, linewidth, and spectral position was investigated in a temperature range from 4 K up to 130 K. Single-photon emission from the quantum dots is presented up to a temperature of 100 K, confirmed by photon-statistics measurements.

Publication: Triggered single-photon emission in the red spectral range from optically excited InP/(Al,Ga)InP quantum dots embedded in micropillars up to 100 K
M. Bommer, W.-M. Schulz, R. Roßbach, M. Jetter, P. Michler, T. Thomay, A. Leitenstorfer, and R. Bratschitsch
externer Link J. Appl. Phys. 110, 063108 (2011)

Contact person: Prof. Dr. Peter Michler

Dephasing of Triplet-Sideband Optical Emission of a Resonantly Driven InAs/GaAs Quantum Dot inside a Microcavity

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Detailed properties of resonance fluorescence from a single quantum dot in a micropillar cavity are investigated, with particular focus on emission coherence in the dependence on optical driving field power and detuning. A power-dependent series over a wide range reveals characteristic Mollow triplet spectra with large Rabi splittings of |Ω|≤15GHz. In particular, the effect of dephasing in terms of systematic spectral broadening ~Ω 2 of the Mollow sidebands is observed as a strong fingerprint of excitation-induced dephasing. Our results are in excellent agreement with predictions of a recently presented model on phonon-dressed quantum dot Mollow triplet emission in the cavity-QED regime.

Publication: Dephasing of Triplet-Sideband Optical Emission of a Resonantly Driven InAs/GaAs Quantum Dot inside a Microcavity
S. M. Ulrich, S. Ates, S. Reitzenstein, A. Löffler, A. Forchel, and P. Michler
externer Link Phys. Rev. Lett. 106, 247402 (2011)

Contact person: Prof. Dr. Peter Michler

Lasing properties of InP/(Ga_0.51In_0.49)P quantum dots in microdisk cavities

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We investigated the photoluminescence from InP quantum dots incorporated in (Ga0.51In0.49)P microdisk structures. With increasing pump power we observe a transition to stimulated emission indicated by the S shape of the input-output curve. This transition is accompanied with a concentration of the emission to one or a few modes exhibiting quality factors on the order of 10 4 at transparency. Time-resolved measurements show that at the same time the photoluminescence decay time considerably decreases. Furthermore, in the transition regime the linewidth of the lasing mode is reduced and the second-order photon correlation function exhibits a reduction of fluctuations as previously reported for lasers with InAs quantum dots in photonic crystal, microdisk and micropillar cavities as the gain medium. The experimental findings are compared with the predictions of a microscopic theory.

Publication: Lasing properties of InP/(Ga_0.51In_0.49)P quantum dots in microdisk cavities
M. Witzany, R. Roßbach, W.-M. Schulz, M.Jetter, P. Michler, T-L. Liu, E. Hu, J. Wiersig, and F. Jahnke
externer Link Phys. Rev. B 83, 205305 (2011)

Contact person: Prof. Dr. Peter Michler

Short wavelength red-emitting AlGaInP-VECSEL exceeds 1.2 W continuous-wave output power

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We present a vertical external cavity surface-emitting laser system based on a multi-quantum-well structure with 20 compressively strained GaInP quantum wells for an operation wavelength of around 665 nm with a monolithic integrated distributed Bragg reflector. With the help of an intra-cavity diamond heatspreader the laser operates in continuous-wave mode. Operation with a TEM 00 Gaussian beam profile and a beam propagation factor of M² <= 1.05 is shown as well as a high resolution spectrum of the laser line, which shows the etalon effect of the diamond. The laser can be operated at a maximum output power exceeding 1.2 W with a slope efficiency of eta diff = 18%. At maximum output power the wavelength of the laser resonance is at 670 nm, which is shortest reported until now at powers exceeding 1 W. By rotating a birefringent filter in an extended folded cavity arrangement a wavelength tuning of 21 nm was attained.

Publication: Short wavelength red-emitting AlGaInP-VECSEL exceeds 1.2 W continuous-wave output power
T. Schwarzbäck, M. Eichfelder, W.-M. Schulz, R. Roßbach, M. Jetter and P. Michler
externer Link Applied Physics B 102, 789 (2011)

Contact person: Roman Bek

Emission characteristics of a highly correlated system of a quantum dot coupled to two distinct micropillar cavity modes

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Nonresonant coupling is a recently discovered phenomenon that allows deeper insight into the interaction of a quantum dot with the surrounding solid state medium. In this work investigations on a quantum dot coupled to two distinct modes of a micro pillar cavity are shown where we focus on the emission characteristics of the quantum dot compared to the two mode emission channels. In cross-correlation measurements, the anti-correlation between all three emission channels is unambiguously demonstrated. While the emission dynamics of the quantum dot is transferred to the spectrally closest mode as proven by temperature-dependent lifetime measurements, the coherence of the mode emission stays at a low constant level unperturbed by the detuning of the emitter to the modes. This effect can be attributed to the additional pure dephasing that the photons undergo while being transferred to either of the modes. Additionally, power-dependent measurements under purely resonant excitation have revealed strong emitter-mode coupling with spectral detunings up to 3.7 meV.

Publication: Emission characteristics of a highly correlated system of a quantum dot coupled to two distinct micropillar cavity modes
S. Weiler, A. Ulhaq, S. M. Ulrich, S. Reitzenstein, A. Löffler, A. Forchel, and P. Michler
Phys. Rev. B 82, 205326 (2010)

Contact person: Prof. Dr. Peter Michler

 

Low-density InP quantum dots embedded in Ga0.51In0.49P with high optical quality realized by a strain inducing layer

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We present a method to reduce the intrinsically high InP quantum dot density embedded in a Ga 0.51In 0.49P barrier by introducing an InGaAs quantum dot seed layer. The additional strain reduces the total InP quantum dot density by around one order of magnitude from 2x10 10 to 3x10 9 cm -2 but only ~1% of the InP nanostructures seem to be optically active (10 7 cm -2). Therefore, microphotoluminescence measurements could be accomplished without masks. We found resolution-limited photoluminescence linewidths (<100 µeV), good signal-to-noise ratios ( ~ 65), single-photon emission behavior (g (2)((t = 0) = 0.3), and excitonic decay times of typically between 1 and 2 ns. Furthermore the structural quantum dot properties were investigated.

Publication: Low-density InP quantum dots embedded in Ga 0.51In 0.49P with high optical quality realized by a strain inducing layer
Daniel Richter, Robert Roßbach, Wolfgang-Michael Schulz, Elisabeth Koroknay, Christian Kessler, Michael Jetter, and Peter Michler
externer Link Applied Physics Letters 97, 063107 (2010)

Contact person: Stefan Hepp

Optical properties of red emitting self-assembled InP/(Al0.20Ga0.80)0.51In0.49P quantum dot based micropillars

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Using focused ion beam etching techniques, micropillar cavities were fabricated from a high reflective AlAs/AlGaAs distributed Bragg reflector planar cavity containing self-assembled InP quantum dots in (Al 0.20Ga 0.80) 0.51In 0.49P barrier layers. The mode spectra of pillars with different diameters were investigated using micro-photoluminescence, showing excellent agreement with theory. Quality factors of the pillar cavities up to 3650 were observed. Furthermore, for a microcavity pillar with 1.26 um diameter, single-photon emission is demonstrated by performing photon correlation measurements under pulsed excitation.

Publication: Optical properties of red emitting self-assembled InP/(Al 0.20Ga 0.80) 0.51In 0.49P quantum dot based micropillars

Wolfgang-Michael Schulz, Tim Thomay, Marcus Eichfelder, Moritz Bommer, Michael Wiesner, Robert Roßbach, Michael Jetter, Rudolf Bratschitsch, Alfred Leitenstorfer, and Peter Michler

 

07 June 2010 / Vol. 18, No. 12 / OPTICS EXPRESS 12543



Contact person: Dr. M. Jetter

Low density MOVPE grown InGaAs QDs exhibiting ultra-narrow single exciton linewidths

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Low density (~10 7 cm -2), small sized InGaAs quantum dots were grown on a GaAs substrate by metal–organic vapor-phase epitaxy and a special annealing technique. The structural quantum dot properties and the influence of the annealing technique was investigated by atomic force microscope measurements. High-resolution micro-photoluminescence spectra reveal narrow photoluminescence lines, with linewidths down to 11 µeV and fine structure splittings of 25 µeV. High signal to noise ratios (~140) and a nearly background free autocorrelation measurement indicate an excellent optical quality and single photon emission behavior. Furthermore, time resolved measurements reveal excitonic decay times typically in the range between 800 and 2300 ps and biexcitonic decay times around 300 ps.

Publication: Low density MOVPE grown InGaAs QDs exhibiting ultra-narrow single exciton linewidths
Daniel Richter, Robert Hafenbrak, Klaus D. Jöns, Wolfgang-Michael Schulz, Marcus Eichfelder, Matthias Heldmaier, Robert Roßbach, Michael Jetter, and Peter Michler
externer Link Nanotechnology 21, 125606 (2010)

Contact person: Stefan Hepp

Triggered single-photon emission from electrically excited quantum dots

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Pulsed electrical excitation of single InP/GaInP quantum dots was used to achieve triggered single-photon emission in the red spectral range with an excitation repetition rate of up to 200 MHz. ncreased repetition rates were prevented by the finite decay-time of the quantum dots, and autocorrelation measurements with excitation rates above 1 GHz look similar to what is expected for dc injection. However, negative voltage pulses can increase the decay-rate considerably such that 1 GHz excitation rates should be possible.

Publication: Triggered single-photon emission from electrically excited quantum dots
M. Reischle, C. Kessler, W.-M. Schulz, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler
externer Link  Applied Physics Letters 97, 143513 (2010)

Contact person: Prof. Dr. Peter Michler

Non-resonant dot-cavity coupling and its potential for resonant single-quantum-dot spectroscopy

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Non-resonant emitter–cavity coupling is a fascinating effect recently observed as unexpected pronounced cavity resonance emission even in strongly detuned single quantum dot–microcavity systems. This phenomenon indicates strong, complex light–matter interactions in these solid-state systems, and has major implications for single-photon sources and quantum information applications.We study non-resonant dot–cavity coupling of individual quantum dots in micropillars under resonant excitation, revealing a pronounced effect over positive and negative quantum dot mode detunings. Our results suggest a dominant role of phonon-mediated dephasing in dot–cavity coupling, giving a new perspective to the controversial discussions ongoing in the literature. Such enhanced insight is essential for various cavity-based quantum electrodynamic systems using emitters that experience phonon coupling, such as colour centres in diamond and colloidal nanocrystals. Non-resonant coupling is demonstrated to be a versatile "monitoring" tool for observing relevant quantum dot s-shell emission properties and background-free photon statistics. In particular, the line broadening of the QD s-shell is “monitored” by the mode signal with high conformity to the directly measured QD linewidth. The mode signal also monitors the saturation behavior of a near Fourier transform-limited photon emission from a resonantly excited QD. We have also investigated the temperature dependence of the coupling mechanism between an off-resonant QD and a cavity mode under pure resonant excitation of the quantum emitter.

Publication: Non-resonant dot-cavity coupling and its potential for resonant single-quantum-dot spectroscopy
S. Ates, S. M. Ulrich, A. Ulhaq, S. Reitzenstein, A. Löffler, S. Höfling, A. Forchel, and P. Michler
externer Link Nature Photonics, Nature Photonics 3, 724-728 (2009)

Contact person: Dr. Sven M. Ulrich and Prof. Dr. P. Michler

Publication: Linewidth broadening and emission saturation of a resonantly excited quantum dot monitored via an off-resonant cavity mode
A. Ulhaq, S. Ates, S. Weiler, S. M. Ulrich, S. Reitzenstein, A. Löffler, S. Höfling, L. Worschech, A. Forchel, and P. Michler
externer Link Phys. Rev. B 82, 045307 (2010)

Contact person: Prof. Dr. P. Michler

 

Post-Selected Indistinguishable Photons from the Resonance Fluorescence of a Single Quantum Dot in a Microcavity

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Applying continuous-wave pure resonant s-shell optical excitation of individual quantum dots in a high-quality micropillar cavity, we demonstrate the generation of post-selected indistinguishable photons in resonance fluorescence. Close to ideal visibility contrast of 90% is verified by polarization-dependent Hong-Ou-Mandel two-photon interference measurements. Furthermore, a strictly resonant continuous wave excitation together with controlling the spontaneous emission lifetime of the single quantum dots via tunable emitter-mode coupling (Purcell) is proven as a versatile scheme to generate close to Fourier transform-limited (T 2/(2T 1) = 0.91) single photons even at 80% of the emission saturation level.

Publication: Post-Selected Indistinguishable Photons from the Resonance Fluorescence of a Single Quantum Dot in a Microcavity
S. Ates, S. M. Ulrich, S. Reitzenstein, A. Löffler, A. Forchel, and P.Michler
externer Link Phys. Rev. Lett. 103, 167402 (2009)

Contact person: Prof. Dr. Peter Michler

Low Threshold InP/AlGaInP Quantum Dot In-Plane Laser Emitting at 638 nm

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Within this contribution, results for a laser structure consisting of InP quantum dots embedded in an (AlxGa1-x)0.51In0.49P matrix lattice matched to GaAs are presented. The structure was fabricated using metal–organic vapor-phase epitaxy, showing electrically pulsed laser operation at room temperature with a low threshold current density of 870 A/cm2 and a lasing wavelength of 638 nm for a 2000 µm long device with uncoated facets. Optical output powers of more than 55 mW per facet and lasing up to 313 K is demonstrated.

Publication: Low Threshold InP/AlGaInP Quantum Dot In-Plane Laser Emitting at 638 nm
Wolfgang-Michael Schulz, Marcus Eichfelder, Robert Roßbach, Michael Jetter, and Peter Michler
externer Link Appl. Phys. Express 2 112501 (2009)

Contact person: Dr. M. Jetter

Room-temperature lasing of electrically pumped red-emitting InP/(Al0.20Ga0.80)0.51In0.49P quantum dots embedded in a vertical microcavity

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We demonstrate electrically pumped laser light emission in the visible red spectral range using self-assembled InP quantum dots embedded in a microcavity mesa realized by monolithically grown high-reflectivity AlGaAs distributed Bragg reflectors. We used common semiconductor laser processing steps to fabricate stand-alone index-guided vertical-cavity surface-emitting lasers with oxide apertures for optical wave-guiding and electrical current constriction. Ultra-low threshold of around 10 A/cm2 and room temperature lasing were demonstrated. Additionally, the temperature independence of the threshold current, which was predicted in theory for quantum dot lasers, is displayed.

Publication: Room-temperature lasing of electrically pumped red-emitting InP/(Al 0.20Ga 0.80) 0.51In 0.49P quantum dots embedded in a vertical microcavity
M. Eichfelder, W.-M. Schulz, M. Reischle, M. Wiesner, R. Roßbach, M. Jetter, and P. Michler
externer Link Applied Physics Letters 95, 131107 (2009)
(Reselected in Virtual Journal of Nanoscale Science & Technology)

Contact person: Mona Stadler

Optical and structural properties of InP quantum dots embedded in (AlxGa1-x)0.51In0.49P

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Within this work we present optical and structural properties of InP quantum dots embedded in (Al xGa 1-x) 0.51In 0.49P barriers. Atomic force microscopy measurements show a mainly bimodal height distribution with aspect ratios (ratio of width to height) of about 10:1 and quantum dot heights of around 2 nm for the smaller quantum dot class (type A) and around 4 nm for the larger quantum dot class (type B). From ensemble photoluminescence measurements we estimated thermal activation energies of up to 270 meV for the type-A quantum dots, resulting in a 300 times higher luminescence intensity at 200 K in comparison to our InP quantum dots in Ga 0.51In 0.49P at the same emission wavelength. Photon statistic measurements clearly display that InP quantum dots in (Al 0.20Ga 0.80) 0.51In 0.49P emit single photons up to 80 K, making them promising candidates for high-temperature single-photon emitters.

Publication: Optical and structural properties of InP quantum dots embedded in (Al xGa 1-x) 0.51In 0.49P
W.-M. Schulz, R. Roßbach, M. Reischle, G. J. Beirne, M. Bommer, M. Jetter, and P. Michler
externer Link Physical Review B 79, 035329, (2009)

Contact person: Dr. M. Jetter

Single Semiconductor Quantum Dots Single Semiconductor Quantum Dots

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This book reviews recent advances in the exciting and rapidly growing field of semiconductor quantum dots via contributions from some of the most prominent researchers in the scientific community. Special focus is given to optical, quantum optical, and spin properties of single quantum dots due to their potential applications in devices operating with single electron spins and/or single photons. This includes single and coupled quantum dots in external fields, cavity-quantum electrodynamics, and single and entangled photon pair generation. Single Semiconductor Quantum Dots also addresses growth techniques to allow for a positioned nucleation of dots as well as applications of quantum dots in quantum information technologies.

Publication: Single Semiconductor Quantum Dots
P. Michler (Ed.):
externer Link Single Semiconductor Quantum Dots, NanoScience and Technology (Springer, Berlin, Heidelberg, 2009)

externer Link book flyer

Contact person: Prof. Dr. P. Michler

The Dark Exciton State in Quantum Dots

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The influence of the dark exciton state on single InP QDs was investigated. The exciton intensity drops sharply compared to the biexciton with rising pulsed laser excitation power while the opposite is true with temperature. Also, the decay rate is faster for the exciton than the biexciton and the dark-to-bright state spin flip is enhanced with temperature. Furthermore, long-lived dark state related memory effects are observed in second-order cross-correlation measurements between the exciton and biexciton. Therefore, future QD devices based on the exciton decay, such as single-photon sources, or on the biexciton-exciton cascade, such as entangled-photon sources, must take the dark state into account.

Publication: Influence of the Dark Exciton State on the Optical and Quantum Optical Properties of Single Quantum Dots
M. Reischle, G. J. Beirne, R. Roßbach, M. Jetter, and P. Michler
externer Link Phys. Rev. Lett. 101, 146402 (2008)

Contact person: Prof. Dr. Peter Michler
 

Electrically pumped single-photon emission

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An electrically pumped single-photon emitter in the visible spectral range, working up to 80 K has been realized using a self-assembled single InP quantum dot embedded in AlGaInP. Aluminum was added to the barrier material in order to provide a higher QD confinement potential.
We confirm that the electroluminescense is emitted from a single quantum dot by performing second-order autocorrelation measurements and show that the deviation from perfect single-photon emission is entirely related to detector limitations and background signal.

Publication: Electrically pumped single-photon emission in the visible spectral range up to 80 K
M. Reischle, G. J. Beirne, W.-M. Schulz, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler
externer Link Opt. Express 16, 12771 (2008)

Contact person: Dr. M. Jetter

Semiconductor-based Entangled Photon Pair Source Influence of the SE coupling factor beta on the coherence length of microcavity lasers

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A systematic experimental and theoretical study of first-order coherence properties of high beta quantum-dot micropillar lasers is presented. A nonlinear increase in the coherence length is found in the transition regime from spontaneous to dominantly stimulated emission. This increase is accompanied by a qualitative change in the first-order field-correlation function from a Gaussian-type profile to an exponential behavior, which is in excellent agreement with a microscopic semiconductor laser theory. Our results also demonstrate a decreasing coherence length with increasing spontaneous emission coupling beta, thus raising questions about the practicability of high beta lasers for device applications.

Publication: Influence of the spontaneous optical emission factor beta on the first-order coherence of a semiconductor microcavity laser
S. Ates, C. Gies, S. M. Ulrich, J. Wiersig, S. Reitzenstein, A. Löffler, A. Forchel, F. Jahnke, and P. Michler
externer Link Phys. Rev. B 78, 155319 (2008)

Contact person: Prof. Dr. Peter Michler

Electrically pumped single-photon emission

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An electrically pumped single-photon emitter in the visible spectral range, working up to 80 K has been realized using a self-assembled single InP quantum dot embedded in AlGaInP. Aluminum was added to the barrier material in order to provide a higher QD confinement potential.
We confirm that the electroluminescense is emitted from a single quantum dot by performing second-order autocorrelation measurements and show that the deviation from perfect single-photon emission is entirely related to detector limitations and background signal.

Publication: Electrically pumped single-photon emission in the visible spectral range up to 80 K
M. Reischle, G. J. Beirne, W.-M. Schulz, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler
externer Link Opt. Express 16, 12771 (2008)

Contact person: Prof. Dr. Peter Michler

Red single-photon emission from an InP/GaInP quantum dot embedded in a planar monolithic microcavity

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Using micro-photoluminescence we demonstrate single-photon emission in the visible (red) spectral range using self-assembled InP quantum dots embedded in a planar microcavity realized by monolithically grown high reflectivity AlGaAs distributed Bragg reflectors. A full width at half maximum of 130 µeV at 5 K was observed from a single quantum dot coupled to the fundamental cavity resonance. Photon correlation measurements performed under continuous wave excitation show a clear antibunching behavior (g²(0)=0.13) as expected for a single-photon emitter. Saturation count rates up to 1.5 MHz (8.1 MHz into the first lens, with an extraction efficiency of 4.1%) were observed.

Publication:
1. Red single-photon emission from an InP/GaInP quantum dot embedded in a planar monolithic microcavity
R. Roßbach, M. Reischle, G. J. Beirne, M. Jetter, and P. Michler
externer Link Appl. Phys. Lett. 92, 071105 (2008)

Contact person: Dr. M. Jetter

Pulsed layer growth of AlInGaN nanostructures

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A pulsed layer growth mode in the MOVPE was used to fabricate excellent quality AlInGaN nanostructures. The amount of material was varied, resulting in AlInGaN layer thicknesses between nominally 1.5 nm and 6 nm, respectively. Analyzing the material properties by x-ray diffraction (XRD) as well as photoluminescence (PL) spectroscopy the high quality of the deposited material could be confirmed. An energetic shift of the resonance lines from 2.65 eV to 3.33 eV with decreasing well thickness was found which was attributed mainly to the presence of internal electric fields at the AlInGaN/GaN interface. Comparing the luminescence at elevated temperatures, the pulsed layer epitaxy structures reveal a much higher intensity as the conventional grown samples.

Publication: Pulsed layer growth of AlInGaN nanostructures
M. Jetter, and P. Michler
externer Link phys. stat. sol. (c) 5, No. 6, 1494 (2008)

Contact person: Dr. M. Jetter

Semiconductor-based Entangled Photon Pair Source

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Self-assembled InGaAs quantum dots can emit two photons that are in a polarization superposition state, a so called EPR or entangled state. In general, this quantum correlation is reduced by a spin coupling of the charge carriers that create these photons after their recombination. A high-resolution photoluminescence measuring technique allows us to determine the size of the resulting fine structure splitting. We were able to verify the conditions of entangled or classically correlated photon pairs in full consistence with observed fine structure properties. Furthermore, we demonstrate reliable polarization entanglement at elevated sample temperatures up to 30 K.

Publication: Triggered polarization-entangled photon pairs from a single quantum dot up to 30 K
R. Hafenbrak, S. M. Ulrich, P. Michler, L. Wang, A. Rastelli and O. G. Schmidt
externer Link New Journal of Physics 9, 315 (2007)

Contact person: Prof. Dr. Peter Michler

Micropillar Laser Photon Emission Statistics

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Detailed measurements of the first- and second-order coherence properties of quantum dot-based micropillar lasers have been performed and interpreted on the basis of a refined semiconductor laser theory. Under increasing optical excitation the transition into lasing is accompanied by both pronounced photon intensity fluctuations and strong coherence length changes. Our investigations clearly visualize a smooth transition from the regime of spontaneous into predominantly stimulated emission, which becomes harder to determine with high beta values. In our theory, a microscopic approach is used to incorporate the semiconductor nature of QDs. The results are in agreement with the experimental intensity traces and the photon statistics measurements.

Publication: Photon Statistics of Semiconductor Microcavity Lasers
S. M. Ulrich, C. Gies, S. Ates, J. Wiersig, S. Reitzenstein, C. Hofmann, A. Löffler, A. Forchel, F. Jahnke, and P. Michler,
externer Link Physical Review Letters 98, 043906 (2007)

Contact person: Prof. Dr. Peter Michler

Micropillar Laser Mode Coherence Properties

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This project addresses the coherence properties of spontaneous and stimulated emission processes from QD-based high quality semiconductor micropillar cavities with elliptical cross-section. Due to the reduced symmetry, a clear polarization splitting of the fundamental emission mode is revealed, in full conformity with an oscillatory behavior found from corresponding g(1)(t) first-order field correlation measurements. In addition, power-dependent g(1)(t) series on a single polarization component of the lasing mode systematically revealed a strong coherence time increase, thus reflecting the change of emission characteristics from thermal to coherent light.

Publication: Coherence properties of high-ß elliptical semiconductor micropillar lasers
S. Ates, S. M. Ulrich, P. Michler, S. Reitzenstein, A. Löffler, and A. Forchel,
externer Link Applied Physics Letters 90, 161111 (2007)

Contact person: Prof. Dr. Peter Michler

High Aspect Ratio InP Single Quantum Dots

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These InP dots have a very high aspect ratio (ratio of width to height) of approximately 27:1. In general, even at high excitation power densities, the dots with ground-state transition energies above 1.82 eV exhibit only s-shell emission, while the larger dots emitting below 1.82 eV tend to exhibit emission from several (in some cases up to eight) shells. Calculations indicate that this change is due to the smaller dots having only one confined election level while the larger dots have two or more. Time-resolved investigations indicate the presence of fast carrier relaxation and recombination processes for both dot types, however, only the larger dots display clear inter-level relaxation effects as expected. Such QDs are interesting as they allow for a large tuning of the electronic interlevel spacing within the dots without significantly shifting the related ground-state emission energy.

Publication: Electronic shell structure and carrier dynamics of high aspect ratio InP single quantum dots
G. J. Beirne, M. Reischle, R. Rossbach, W. M. Schulz, M. Jetter, J. Seebeck, P. Gartner, C. Gies, F. Jahnke, and P. Michler
externer Link Physical Review B 75, 195302 (2007)

Related work: Single-photon emission from a type-B InP/GaInP quantum dot
G. J. Beirne, P. Michler, M. Jetter, and H. Schweizer
externer Link Journal of Applied Physics 98, 093522 (2005)

Contact person: Prof. Dr. Peter Michler

Semipolar GaInN/GaN Multi-quantum Well Structures

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The carrier lifetime and photoluminescence intensity of semi-polar GaInN/GaN multi-quantum wells (MQWs) has been investigated. The MQWs of both samples are overgrown by a Mg-doped GaN layer in order to form a light emitting diode (LED) structure. The stripes have a triangular shape. The PL decay time is reduced in the case of the semi-polar sample by almost two orders of magnitude to 650 ps at 4 K as a result of the much reduced piezoelectric field. The PL intensity of the semi-polar sample is subsequently more than double that of the polar sample as a result of the improved recombination probability.

Publication: Time- and locally resolved photoluminescence of semipolar GaInN/GaN facet light emitting diodes
T. Wunderer, P. Brückner, J. Hertkorn, F. Scholz, G. J. Beirne, M. Jetter, P. Michler, M. Feneberg, and K. Thonke,
externer Link Applied Physics Letters 90, 171123 (2007)

Contact person: Dr. Michael Jetter

InP Asymmetric Quantum Dot Pairs InP Asymmetric Quantum Dot Pairs

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Single pairs of vertically stacked asymmetric InP quantum dots embedded in GaInP barriers have been investigated as a function of the inter-dot spacer thickness. Time-integrated and time-resolved photoluminescence measurements have been performed with the former showing a change of the intensity ratio between the two dots and the latter an increasing difference in the photoluminescence decay-time of the two dots with decreasing spacer thickness. Hence, we suggest transitions from vanishing tunnel-coupling to electron tunneling and finally to electron and hole tunneling for successively smaller barrier widths. The results clearly show the nonresonant character of the tunneling process which is due to the different ground state energies (different by approx. 40 meV) of the unequally sized dots.

Publication: Nonresonant tunneling in single asymmetric pairs of vertically stacked InP quantum dots
M. Reischle, G. J. Beirne, R. Roßbach, M. Jetter, H. Schweizer, and P. Michler
externer Link Physical Review B 76, 085338 (2007)

Contact person: Prof. Dr. Peter Michler

QD Emission Control and Fine Structure Tuning by Lateral Electric Fields

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The quantum-confined Stark effect (QCSE) of excitonic states in self-assembled (In,Ga)As/GaAs quantum dots was studied by microphotoluminescence spectroscopy. A similar Stark-shift behavior for excitons, biexcitons, and a charged state has been observed. Our investigations suggest the absence of a permanent dipole moment in the lateral quantum dot plane. Values of the polarizability could be derived for all the investigated states.
In addition, high-resolution Fabry-Pérot interferometry was applied to investigate the excitonic fine structure under the influence of a lateral electric field. For a single dot, the splitting could even be tuned to zero, thus affording the possibility to create electrically controlled entangled photon pairs.

Publication: Influence of lateral electric fields on multiexcitonic transitions and fine structure of single quantum dots
M. M. Vogel, S. M. Ulrich, R. Hafenbrak, P. Michler, L. Wang, A. Rastelli, and O. G. Schmidt
externer Link Applied Physics Letters 91, 051904 (2007)

Contact person: Prof. Dr. Peter Michler

Site-controlled pyramidal nanostructures

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We have fabricated site-controlled nitride nanostructures by deposition of GaInN on GaN micro pyramids by selective metal-organic vapor-phase epitaxy on sapphire. The nature of the growth process implies the formation of quantum wells on the sidewalls of the pyramid, quantum wires at its edges and a quantum dot on the tip of the pyramid. The luminescence properties of these structures confirm the existence of regions with different dimensionality.

Publication:
1. Carrier dynamics in site-controlled Ga1-xInxN quantum dots
M. Jetter, V. Pérez-Solórzano, A. Gröning, H. Gräbeldinger, M. Ubl, and H. Schweizer
externer Link phys. stat. sol. (c), 3, No. 6, S. 2060 (2006)

2. Selective Growth of GaInN Quantum Dot Structures
M. Jetter, V. Pérez-Solórzano, A. Gröning, M. Ubl, H. Gräbeldinger and H. Schweizer
externer Link J. Crystal Growth 272 (2004) 204

Related work:
1. Regions of different confinement in low-dimensional AlInGaN quantum structures
A. Gröning, V. Pérez-Solórzano, M. Jetter, and H. Schweizer
externer Link Advances in OptoElectronics, vol 2007, Article ID 69568, (2007)

Contact person: Dr. M. Jetter

Lateral Quantum Dot Molecules

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Self-assembled lateral quantum dot molecules that are fabricated by a unique combination of quantum dot growth and atomic layer precise in-situ etching are studied using micro-photoluminescence experiments. The electronic coupling of charge carriers confined in quantum dot molecules is observed using photon correlation experiments. By applying a lateral electric field an electron can be reversibly transferred from one dot to the other. This control potentially allows for the use of such artificial molecules as the basic building block of a quantum computer, that is, as a quantum gate or as a tunable single-photon source. A recent progress could be achieved in embedding the dot molecules in a planar cavity structure which led to a 30 times enhancement of the single-photon emission rate up to almost 1 MHz.

Publication:
1. Quantum Light Emission of Two Lateral Tunnel-Coupled (In,Ga)As/GaAs Quantum Dots Controlled by a Tunable Static Electric Field
G. J. Beirne, C. Hermannstädter, L. Wang, A. Rastelli, O. G. Schmidt, and P. Michler,
externer Link Physical Review Letters 96, 137401 (2006)

2. Polarization fine-structure and enhanced single-photon emission of self-assembled lateral InGaAs quantum dot molecules embedded in a planar micro-cavity
C. Hermannstädter, M. Witzany, G. J. Beirne, W.-M. Schulz, M. Eichfelder, R. Rossbach, M. Jetter, P. Michler, L. Wang, A. Rastelli, and O. G. Schmidt
externer Link Journal of Applied Physics 105, 122408 (2009).

Contact person: Prof. Dr. Peter Michler

Structural and optical characterization of (AlIn)GaN quantum dots

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AlyInxGa1-x-yN quantum dots have been grown by MOVPE on (0001) sapphire substrates and the dependence of the self-assembled QDs density and height on the growth conditions was investigated. A maximum dot density of 4·1010cm-2 was achieved. The optical properties were studied after overgrowing the QDs with a GaN cap layer, where very intense luminescence in the region between 2.4 and 2.8 eV could be found.

Publication: Structural- and optical characterization of AlyInxGa1-x-yN quantum dots
V. Pérez-Solórzano, A. Gröning, H.Schweizer, and M. Jetter
externer Link phys. stat. sol. (c), 3, No. 6, S. 2073 (2006)

Contact person: Dr. M. Jetter

Epitaxy and processing of red VCSEL

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Red VCSEL emitting around 660 nm are grown by MOVPE to provide a fast and powerful emitter device for data transmission via polymer optical fibers (POF). The 8-9 µm thick structure consists out of around 180 layers which we control during growth with an in-situ measurement setup to achieve a very high accuracy. By using a heat dissipation model the diameters of the oxide aperture and the mesa could be optimized resulting in continuous-wave lasing operation up to 70°C at 660 nm. In pulsed mode the AlGaInP-based active zone showed lasing up to 170°C. For data transmission the VCSEL were modulated in small-signal modulation up to a bandwidth of 5 GHz. For large-signal modulation we obtained at 1.25 Gbit/s wide open eyes and even at 2.1 Gbit/s a bit error free data transmission was possible.

Publication:
1. Red VCSEL for High-Temperature Applications
R. Roßbach, T. Ballmann, R. Butendeich, H. Schweizer, F. Scholz and M. Jetter
externer Link J. Crystal Growth 272 (2004)

2. Analog Modulation of 650 nm VCSEL
T. Ballmann, R. Roßbach, R. Butendeich, B. Raabe, M. Jetter, F. Scholz, and H. Schweizer
externer Link IEEE Photonics Technology Letters 18, S. 583 (2006)

3. Rote VCSEL für Hochgeschwindigkeits-Datenübertragung über POF
M. Jetter, R. Roßbach, P. Michler
externer Link Photonik 1, 56 (2008)
Download PDF-Dokument

Contact person: Dr. M. Jetter

InP quantum dots in the visible spectral range

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InP quantum dots have been grown in the Stranski-Krastanow growth mode by MOVPE. As the surrounding barrier material we used AlxGaInP barriers with different Al-content. With this method we could achieve photoluminescence from red to the green spectral range. By using a novel AlGaInP/AlInP distributed Bragg reflector in the green spectral range we could increase the luminescence intensity by nearly a factor of two.

Publication:
1. Red to Green Photo­luminescence of InP-­Quantum Dots in AlxGa1-xInP
R. Roßbach, W.­M. Schulz, M. Reischle, G. J. Beir­ne, M. Jetter and P. Michler
externer Link J. Cryst. Growth, 298, p. 595, (2007)

2. Green Photoluminescence of Single InP-­Quantum Dots grown on Al0.66Ga0.33InP/AlInP Distributed Bragg Reflectors
R. Roßbach, W.­M. Schulz, M. Jetter, and P. Mich­ler
externer Link J. Cryst. Growth, 298, p. 599, (2007)

Contact person: Dr. M. Jetter

InP quantum dot molecules

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Larger and smaller InP quantum dots were grown on top of each other on GaInP separated by a GaInP spacer layer. TEM measurements showed that the smaller quantum dot is positioned on top of the underlying larger quantum dot. We observed in power dependent ensemble measurements that for thick spacer layers both ensembles increase independently. For thin spacer layers photoluminescence of the smaller QD layer at 1.89 eV is detected only at high excitation powers indicating a tunnelling process in between the two different QD layers. Time-resolved ensemble measurements confirmed our assumptions.

Publication: Vertical asymmetric double Quantum Dots
R. Roßbach, M. Reischle, G. J. Beirne, H. Schweizer, M. Jetter and P. Michler
externer Link J. Cryst. Growth, 298, p. 603, (2007)

Contact person: Dr. M. Jetter