M. Eichfelder

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

We report on in-lab free space quantum key distribution (QKD) experiments over 40cm 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 27.2kbits 1 (35.4kbits 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

Electrically pumped single-photon emission in the visible spectral range up to 80 K

We present an electrically pumped single-photon emitter in the visible spectral range, working up to 80 K, realized using a self-assembled single InP quantum dot. 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. Emission from both neutral and charged exciton complexes was observed with their relative intensites depending on the injection current and temperature.

Triggered single-photon emission from electrically excited quantum dots in the red spectral range

Pulsed electrical excitation was used to excite single InP/Ga0.51In0.49P quantum dots and obtain triggered single-photon emission in the red spectral range at an excitation repetition rate of up to 200 MHz. Increased repetition rates are prevented by the finite decay-time, and autocorrelation measurements look similar to what is expected for dc injection above 1 GHz. Finally, it is shown that negative voltage pulses can increase the decay-rate considerably such that 1 GHz excitation rates should be possible.

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

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.

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

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 (GaxIn1−x)0.5P0.5/[(AlxGa1−x)yIn1−y]0.5P0.5 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.

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

Low density (approximately 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 microeV and fine structure splittings of 25 microeV. High signal to noise ratios (approximately 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.

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

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.

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

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(0.20)Ga(0.80))(0.51)In(0.49)P 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 mum diameter, single-photon emission is demonstrated by performing photon correlation measurements under pulsed excitation.

InP quantum dots for applications in laser devices and future solid-state quantum gates

Single and stacked layers of InP quantum dots in (AlxGa1−x)0.51In0.49P barriers were grown by metal-organic vapor-phase epitaxy for applications in semiconductor laser devices and optical gate structures. An in-plane laser structure with a single layer of InP QDs is presented, emitting at 1.942 eV and exhibiting low threshold current densities of 780 A/cm2 in electrically pulsed laser operation at 288 K for a 2000μm long device with uncoated facets. In order to realize an externally driven optical gate structure the stacking behavior of InP in (AlxGa1−x)0.51In0.49P barriers was investigated. To ensure the optical addressability of each quantum dot layer, a special double dot structure where the high energetic smaller sized quantum dot is situated above the low energetic larger sized dot, was produced. The coupling between these quantum dots can be adjusted by the thickness of the spacer layer. The structures are embedded in a ni-Schottky structure and the influence of an external electric field on the emission of the quantum dot ensemble is investigated.

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

In this letter, we report about 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.