GaAs-based edge-emitting diode lasers designed for the near-infrared spectral region usually contain waveguide and cladding layers consisting of AlxGa1-xAs. AlxGa1-xAs-on-GaAs is known to be almost perfectly lattice matched. We have grown AlxGa1-xAsyP1-y/AlxGa1-xAs test samples targeting a partial compensation of the room temperature wafer bow by incorporating up to 4% phosphorus in Al0.85GaAs. The proposed strain compensation scheme has been applied in complete laser devices by partially replacing Al0.85Ga0.15As with Al0.85Ga0.15AsyP1-y. The results will be discussed.

Coupling of acoustic and optical phonons to excitons in single InGaAs/GaAs quantum dots is investigated in detail experimentally and theoretically as a function of temperature. For the theoretical description of the luminescence spectrum, including acoustic and optical phonon scattering, we used the exactly solvable independent boson model. Surprisingly, only GaAs bulk-type longitudinal-optical (LO) phonons are detected in experiment. A quantitatively correct theoretical description of the optical-phonon replica is obtained by including a limited lifetime of the phonons and the dispersion of the LO phonon energy. Similarly, a numerically correct description of the acoustic phonon wings is again based on GaAs bulk material parameters for the phonon dispersion and deformation coupling. In addition, the line shape of the calculated spectra agrees with experiment only when realistic wave functions (e.g., based on eight-band $k\ifmmode\cdot\else\textperiodcentered\fi{}p$ theory) are used for the electron-phonon coupling matrix elements. Gaussian wave functions describing the ground state of a harmonic oscillator fail to describe high-energy tails. Thus, fundamental insights of importance for the correct prediction of properties of nonclassical light sources, based on semiconductor nanostructures, are obtained.

We realized a fast single-photon source based on self-organized quantum dots (QDs). In a p-i-n structure a single electron and a single hole are funnelled into a single InAs quantum dot using a submicron AlO(X) current aperture. The out-coupling efficiency and emission rate are increased by embedding the single-photon source (SPS) into a micro-cavity of Q = 140. The resulting resonant single-QD diode generates single polarized photons at a repetition rate of 1 GHz exhibiting a second-order correlation function of g((2))(0) = 0. The measured optical response is usually limited by the time resolution of available single-photon detectors based on avalanche diodes. Here we present ultra-fast g((2)) correlation functions, obtained with novel superconducting detectors.

Electrically driven single photon sources based on single quantum dot RCLED are reported. The device consists of a GaAs layer with low density of InAs QDs, a 60 nm-thick AlGaAs aperture layer with high aluminum content, p and n type GaAs electrical contact layers. The aperture is used to confine the electric current in order to address a single QD.

In this letter, we demonstrate that self-organized InGaAs quantum dots (QDs) grown on GaAs (111) substrate using droplet epitaxy have great potential for the generation of entangled photon pairs. The QDs show spectrally sharp luminescence lines and low spatial density. A second order correlation value of g(2)(0)<0.3 proves single-photon emission. By comparing the power dependence of the luminescence from a number of QDs we identify a typical luminescence fingerprint. In polarization dependent microphotoluminescence studies a fine-structure splitting ranging ≤40 μeV down to the determination limit of our setup (10 μeV) was observed.

Here we present the first successful growth and spectroscopic investigation of In(Ga)As/GaAs (111) quantum dots (QD). These QD were recently predicted as promising emitters of entangled photon pairs due to their intrinsic threefold degenerate symmetry resulting in zero fine structure splitting (FSS). Low spatial densities of the QDs were grown by droplet epitaxy in an MBE system. Emission of truly single photons is proved by correlation measurements. Using spatially-resolved power- and polarization- dependent experiments we discovered the characteristic excitonic luminescence fingerprints from a number of QDs. Excitonic FSS below 10 μeV, our resolution limit, is observed in agreement with our predictions.

Efficient generation of polarized single photons or entangled photon pairs is a crucial requirement for the implementation of quantum key distribution (QKD) systems [1] [2]. In this context, self-organized semiconductor quantum dots (QDs) [3] [4] play a decisive role as they are capable of emitting only one polarized photon at a time using appropriate electrical current injection [5] [6]. Therefore, a single QD embedded in a LED can be used as a single photon source. By tuning the electronic structure it is possible to use QD as source for entangled photons. Resonant cavity-induced enhancement of spontaneous emission and out-coupling efficiency can improve external quantum efficiency of quantum dot based single photon sources dramatically. In order to optimise the device geometry detailed numerical device modelling must be performed. The modelling of the electromagnetic field were done using eigenmode-techniques. The essential design parameters, such as cavity length, aperture diameter, position and thickness were systematically varied. We designed and fabricated optimized resonant cavity light emitting diodes combined with a submicron oxide current aperture, to pump individual InGaAs/GaAs QDs electrically. These devices demonstrates more than ten times increased single photon rate in comparison to the simple LED design. Pulsed correlation measurements demonstrated true single photon emission with g2(0) = 0 at a rate of 1 GHz.

A resonant cavity light emitting diode combined with a submicron oxide current aperture, to pump individual InGaAs/GaAs quantum dots electrically, has been designed and fabricated. Pulsed correlation measurements demonstrated true single photon emission with g2(0)=0 at a rate of 1=GHz.

Self-organized In(Ga)As/GaAs quantum dots (QDs) grown on (111) substrate are proposed as ideal sources for the generation of entangled photon pairs. Due to the threefold rotational symmetry of the (111) surface, QDs with ${C}_{3v}$ symmetry or higher are expected to develop during growth. In contrast to QDs on (001)-oriented substrates, the symmetry of the confinement potential of (111) QDs is not lowered by piezoelectric effects. As a result the excitonic bright splitting vanishes and the $\text{biexciton}\ensuremath{\rightarrow}\text{exciton}\ensuremath{\rightarrow}0$ recombination cascade can be used for the generation of entangled photons. We evaluate the spectroscopic separability of excitonic and biexcitonic emissions as a function of QD size, shape, and composition using the configuration-interaction model in conjunction with eight-band $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ theory. The piezoelectric field in (111) QDs predominantly aligns along the growth direction and gives rise to vertical charge separation. First- and second-order piezoelectric fields are oriented in opposite directions. The In/Ga ratio inside the QD determines the leading contribution and can be employed to balance both terms in order to achieve a field-free situation with maximal electron-hole overlap. The biexciton binding energy depends on the net piezoelectric potential drop across the QD vertical extension and becomes maximal if the first- and second-order fields outweigh each other within the QD interior.

The efficient generation of polarized single or entangled photons is a crucial requirement for the implementation of quantum key distribution (QKD) systems. Self-organized semiconductor quantum dots (QDs) are capable of emitting one polarized photon or an entangled photon pair at a time using appropriate electrical current injection. We realized a highly efficient single-photon source (SPS) based on well-established semiconductor technology: In a pin structure, a single electron and a single hole are funneled into a single InAs QD using a submicron AlOx current aperture. Efficient radiative recombination leads to emission of single polarized photons with an all-time record purity of the spectrum. Non-classicality of the emitted light without using additional spectral filtering is demonstrated. The out-coupling efficiency and the emission rate are increased by embedding the SPS into a micro-cavity. The design of the micro-cavity is based on detailed modeling to optimize its performance. The resulting resonant single-QD diode is driven at a repetition rate of 1 GHz, exhibiting a second-order correlation function of g(2)(0) = 0. Eventually, QDs grown on (111)-oriented substrates are proposed as a source of entangled photon pairs. Intrinsic symmetry-lowering effects leading to the splitting of the exciton bright states are shown to be absent for this substrate orientation. As a result, the XX rarr X rarr 0 recombination cascade of a QD can be used for the generation of entangled photons without further tuning of the fine-structure splitting via QD size and/or shape.

Highly efficient single photon sources are of particular importance for quantum cryptography and quantum computation. Cavity-induced enhancement of spontaneous emission can improve photon generation efficiency in quantum-dot-based single photon sources dramatically. Using the eigenmode-technique, the authors calculate the 3-D distribution of the optical electromagnetic field inside a RCLED-type single photon source and consequently the Purcell-factor as a function of the wavelength. Under systematic variation of device design parameters such as cavity length and aperture diameter, an optimized device design was determined, providing Purcell-factors up to 5.5.

Low transparency current density and improved temperature stability with a large characteristic temperature T/sub 0/>650 K up to 80/spl deg/C are demonstrated for 1.3 /spl mu/m MBE grown QD-edge emitters. Digital modulation with an open eye pattern up to 12 Gb/s at room temperature and bit error rate below 10/sup -12/ for a 10 Gb/s modulation was realized for this wavelength. Semiconductor optical amplifiers based on InGaAs QDs achieved a chip gain of 28 dB. Conventionally doped semiconductor DBR QD-VCSEL containing 17 p-modulation doped QD layers demonstrated a CW output power of 1.7 mW and differential efficiency of 20 % at 20/spl deg/C. First MOCVD grown QD-VCSEL with selectively oxidized DBRs and 9 QD-layers were realized, emission was at 1.1 /spl mu/m. A CW multimode output power of 1.5 mW and external efficiency of 45 % was achieved at 20/spl deg/C. The minimum threshold current from a device with 2 /spl mu/m aperture was 85 /spl mu/A.

HL 31.1 Wed 14:45 H17 Measurement and control of spin and charge interactions in a single quantum dot molecule — •Emily Clark1, Hubert Krenner1, Christoph Scheurer2, Toshihira Nakaoka3, Max Bichler1, Gerhard Abstreiter1, and Jonathan Finley1 — 1Walter Schottky Institut, Technical University of Munich, Am Coulombwall 3, 85748 Garching, Germany — 2Lehrstuhl für Theoretische Chemie, Technische Universität München, Lichtenbergstraße 4, 85748 Garching, Germany — 3University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo, 153-8505, Japan

1.5 mu m range laser heterostructures based on InAs/InGaAs QDs were grown on metamorphic (NW) (In,Ga,AI)As layers deposited on GaAs substrates using a defect reduction technique (DRT). The analysis of spontaneous emission efficiency corroborates the high contribution of non-radiative recombination in the total recombination current even at high current densities. Lasers showed record characteristics such as: pulsed output power > 7 W and cw output power > 220 mW, high degradation stability (> 800 h of cw operation at similar to 50 mW at 60 degrees C junction temperature), modulation bandwidth of similar to 3 GHz limited by device overheating and the open-eye diagram at 2.5 Gbit/s.

Easy to handle light sources with non-classical emission features are strongly demanded in the growing field of quantum communication. We report on single-photon emission from an electrically pumped quantum dot with unmatched spectral purity, making spatial or spectral filtering dispensable.

We report on a miniature solid state emitter structure, which allows electrical pumping of only one single InAs quantum dot (QD) grown in the Stranski-Krastanow mode. The emitter demonstrates a strongly monochromatic polarized emission of a single QD exciton. Correlation measurements of the emitted photons show a clear antibunching behavior. The structure is thus attractive for practical implementation as effective single photon source for quantum cryptography. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A report is presented of a subminiature solid-state emitter structure, which allows electrical pumping of only one single InAs quantum dot (QD) grown in the Stranski-Krastanow mode. The emitter demonstrates a strongly monochromatic polarised emission of a single QD exciton. No other emission is observed across 500 am. The structure is thus attractive for practical implementation as an effective single photon source for quantum cryptography.

Narrow ridge lasers of 1.5μm range based on InAs∕InGaAs quantum dots grown on metamorphic (In,Ga,Al)As layers deposited on GaAs substrates using defect reduction technique are studied. It is shown that the lasers operate continuous wave (cw) in a single transverse mode. Single-mode 800mW output power in the pulsed regime is obtained for a 6μm ridge width. The dynamic studies of the lasers show a modulation bandwidth of ∼3GHz. Aging tests demonstrate >800h of cw operation at ∼50mW at 10°C (60°C) and >200h at 20°C (70°C) heat sink (junction) temperature without noticeable degradation.

Ground state lasing of electrically driven vertical-cavity surface-emitting lasers with a quantum-dot (QD) gain medium grown using metal-organic vapor phase epitaxy was realized. The devices use stacked InGaAs QD layers, placed in the field intensity antinodes of the cavity formed by selectively oxidized distributed Bragg reflectors. Devices with 3×3 QD layers demonstrate at 20°C a cw output power of 1.45mW at 1.1μm emission wavelength. The peak external efficiency was 45%, limited by lateral carrier spreading within the 4λ cavity and a reduction of the internal efficiency above 60°C. A minimum threshold current of 85μA was obtained from a device with a 1μm aperture.