Strong amplitude-phase coupling in submonolayer quantum dots

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 109, 201102 (2016) and may be found at https://doi.org/10.1063/1.4967833.Submonolayer quantum dots promise to combine the beneficial features of zero- and two-dimensional carrier confinement. To explore their potential with respect to all-optical signal processing, we investigate the amplitude-phase coupling (α-parameter) in semiconductor optical amplifiers based on InAs/GaAs submonolayer quantum dots in ultrafast pump-probe experiments. Lateral coupling provides an efficient carrier reservoir and gives rise to a large α-parameter. Combined with a high modal gain and an ultrafast gain recovery, this makes the submonolayer quantum dots an attractive gain medium for nonlinear optical signal processing

High-power semiconductor disk laser based on InAs∕GaAs submonolayer quantum dots

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 92, 101123 (2008) and may be found at https://doi.org/10.1063/1.2898165.An optically pumped semiconductor disk laser using submonolayer quantum dots (SML QDs) as gain medium is demonstrated. High-power operation is achieved with stacked InAs∕GaAs SML QDs grown by metal-organic vapor-phase epitaxy. Each SML-QD layer is formed from tenfold alternate depositions of nominally 0.5 ML InAs and 2.3 ML GaAs. Resonant periodic gain from a 13-fold nonuniform stack design of SML QDs allows to produce 1.4W cw at 1034nm. The disk laser demonstrates the promising potential of SML-QD structures combining properties of QD and quantum-well gain media for high-power applications.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/FP6/016769/EU/Nano-Photonics Materials and Technologies for Multicolor High-Power Sources/NATA

Temperature-stable operation of a quantum dot semiconductor disk laser

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 93, 051104 (2008) and may be found at https://doi.org/10.1063/1.2968137.We demonstrate temperature-independent output characteristics of an optically pumped semiconductor disk laser (SDL) based on quantum dots (QDs) grown in the Stranski-Krastanow regime. The gain structure consists of a stack of 7×3 QD layers, each threefold group being located at an optical antinode position. The SDL emits at 1210nm independent of the pump power density. Threshold and differential efficiency do not dependent on heat sink temperature. Continuous-wave operation close to 300mW output power is achieved using the ground-state transition of the InGaAs QDs.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/FP6/016769/EU/Nano-Photonics Materials and Technologies for Multicolor High-Power Sources/NATA

Improved threshold of buried heterostructure InAs/GaInAsP quantum dot lasers

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 109, 083104 (2011) and may be found at https://doi.org/10.1063/1.3574406.The parameters for reducing the threshold current density of InAs/InGaAsP/InP quantum-dot (QD) lasers suitable for high temperature operation are studied. The structures were grown using metalorganic vapor phase epitaxy. Increasing the number of QD layers leads to a substantial improvement of the optical confinement and a markedly reduced threshold per dot layer in broad area devices. A reduction of the spacer thickness between the QD layers was not found to significantly affect device characteristics. Depending upon the device length, an optimum number of QD layers was deduced. Based upon optimized QD stacks, buried-heterostructure lasers with a medium device length emitting at 1.5 μm were fabricated. Laterally single-mode devices show promising low threshold currents near 10 mA and good thermal stability with a characteristic temperature of 65 K up to 90 °C.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Bow-tie optical antenna probes for single-emitter scanning near-field optical microscopy

A method for the fabrication of bow-tie optical antennas at the apex of pyramidal Si3N4 atomic force microscopy tips is described. We demonstrate that these novel optical probes are capable of sub-wavelength imaging of single quantum dots at room temperature. The enhanced and confined optical near-field at the antenna feed gap leads to locally enhanced photoluminescence (PL) of single quantum dots. Photoluminescence quenching due to the proximity of metal is found to be insignificant. The method holds promise for single quantum emitter imaging and spectroscopy at spatial resolution limited by the engineered antenna gap width exclusively

Prospects of resonant optical antennas for nano-analysis

Suitably shaped metal nanostructures act as resonant optical antennas that efficiently collect light and confine it to a subwavelength volume. Vice versa, light emission from nano volumes can be enhanced by coupling to antenna structures. We give a short introduction to antenna theory and discuss recent experiments that show the feasibility of achieving strong field enhancement using resonant dipole antennas for near infrared wavelengths. By scanning an optical antenna fabricated at the apex of an AFM tip over individual quantum dots, we observe enhanced emission of the latter while it is in close proximity of the antenna feed gap. Resonant optical antennas hold promise to be applied for spectroscopic characterization of nano structures with high spatial resolutions and single-molecule sensitivity

Radiation from Accelerated Particles in Relativistic Jets with Shocks, Shear-flow, and Reconnection

We have investigated particle acceleration and shock structure associated with an unmagnetized rel-ativistic jet propagating into an unmagnetized plasma for electron-positron and electron-ion plasmas. Strong magnetic fields generated in the trailing jet shock lead to transverse deflection and acceleration of the electrons. We have self-consistently calculated the radiation from the electrons accelerated in the turbulent magnetic fields for different jet Lorentz factors. We find that the synthetic spectra depend on the bulk Lorentz factor of the jet, the jet temperature, and the strength of the magnetic fields generated in the shock. We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic (core) jet and an unmagnetized sheath plasma. We discuss particle acceleration in collimation shocks for AGN jets formed by relativistic MHD simulations. Our calculated spectra should lead to a better understanding of the complex time evolution and/or spectral structure from gamma-ray bursts, relativistic jets, and supernova remnants

Spatial structure of In0.25Ga0.75As/GaAs/GaP quantum dots on the atomic scale

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 102, 123102 (2013) and may be found at https://doi.org/10.1063/1.4798520.In0.25Ga0.75As/GaAs quantum dots grown by metalorganic vapor-phase epitaxy in a GaP matrix have been investigated on the atomic scale using cross-sectional scanning tunneling microscopy. The quantum dots have a truncated pyramidal shape with a reversed cone stoichiometry profile. All deposited indium is found within the quantum dots and the occasionally observed quantum rings, while the wetting layer has a GaAsP composition without any indium inside. This indicates an intense lateral material transfer during growth.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Electrically driven single photon source based on a site-controlled quantum dot with self-aligned current injection

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 101, 211119 (2012) and may be found at https://doi.org/10.1063/1.4767525.Electrical operation of single photon emitting devices employing site-controlled quantum dot (QD) growth is demonstrated. An oxide aperture acting as a buried stressor structure is forcing site-controlled QD growth, leading to both QD self-alignment with respect to the current path in vertical injection pin-diodes and narrow, jitter-free emission lines. Emissions from a neutral exciton, a neutral bi-exciton, and a charged exciton are unambiguously identified. Polarization-dependent measurements yield an exciton fine-structure splitting of (84 ± 2) μeV at photon energies of 1.28–1.29 eV. Single-photon emission is proven by Hanbury Brown and Twiss experiments yielding an anti-bunching value of g(2)(0) = 0.05 under direct current injection.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Fast gain and phase recovery of semiconductor optical amplifiers based on submonolayer quantum dots

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 107, 201102 (2015) and may be found at https://doi.org/10.1063/1.4935792.Submonolayer quantum dots as active medium in opto-electronic devices promise to combine the high density of states of quantum wells with the fast recovery dynamics of self-assembled quantum dots. We investigate the gain and phase recovery dynamics of a semiconductor optical amplifier based on InAs submonolayer quantum dots in the regime of linear operation by one- and two-color heterodyne pump-probe spectroscopy. We find an as fast recovery dynamics as for quantum dot-in-a-well structures, reaching 2 ps at moderate injection currents. The effective quantum well embedding the submonolayer quantum dots acts as a fast and efficient carrier reservoir.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeDFG, 87159868, GRK 1558: Kollektive Dynamik im Nichtgleichgewicht: in kondensierter Materie und biologischen Systeme