GaAs nanowires with elongated cross sections are formed using a catalyst-free growth technique. This is achieved by patterning elongated nanoscale openings within a silicon dioxide growth mask on a ...(111)B GaAs substrate. It is observed that MOVPE-grown vertical nanowires with cross section elongated in the 21̅1̅ and 1̅12 directions remain faithful to the geometry of the openings. An InGaAs quantum dot with weak radial confinement is realized within each nanowire by briefly introducing indium into the reactor during nanowire growth. Photoluminescence emission from an embedded nanowire quantum dot is strongly linearly polarized (typically >90%) with the polarization direction coincident with the axis of elongation. Linearly polarized PL emission is a result of embedding the quantum dot in an anisotropic nanowire structure that supports a single strongly confined, linearly polarized optical mode. This research provides a route to the bottom-up growth of linearly polarized single photon sources of interest for quantum information applications.
InAsP quantum dot lasers grown by MOVPE Karomi, Ivan; Smowton, Peter M; Shutts, Samuel ...
Optics express,
2015-Oct-19, 2015-10-19, 20151019, Letnik:
23, Številka:
21
Journal Article
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We report on InAsP quantum dot lasers grown by MOVPE for 730-780 nm wavelength emission and compare performance with InP dot samples grown under similar conditions and with similar structures. 1-4 mm ...long, uncoated facet InAsP dot lasers emit between 760 and 775 nm and 2 mm long lasers with uncoated facets have threshold current density of 260 Acm(-2), compared with 150 Acm(-2) for InP quantum dot samples, which emit at shorter wavelengths, 715-725 nm. Pulsed lasing is demonstrated for InAsP dots up to 380 K with up to 200 mW output power. Measured absorption spectra indicate the addition of Arsenic to the dots has shifted the available transitions to longer wavelengths but also results in a much larger degree of spectral broadening. These spectra and transmission electron microscopy images indicate that the InAsP dots have a much larger degree of inhomogeneous broadening due to dot size variation, both from layer to layer and within a layer.
This letter reports on InP/GaInP quantum dot modelocked lasers emitting in the 730 nm wavelength region, extending the spectral range of previously reported monolithic mode-locked edge-emitting ...lasers. Modal gain and absorption measurements were used to identify a relatively broad spectrum which is utilised to support passive mode-locking in a monolithically integrated two-section ridge laser. The conditions for mode-locking were explored by varying the current to the gain section and reverse bias to the absorber section. For a total cavity length of 3 mm, the shortest pulse train observed was 6 ps in duration with a repetition rate of 12.55 GHz.
Quantum networks are essential for realising distributed quantum computation and quantum communication. Entangled photons are a key resource, with applications such as quantum key distribution, ...quantum relays, and quantum repeaters. All components integrated in a quantum network must be synchronised and therefore comply with a certain clock frequency. In quantum key distribution, the most mature technology, clock rates have reached and exceeded 1GHz. Here we show the first electrically pulsed sub-Poissonian entangled photon source compatible with existing fiber networks operating at this clock rate. The entangled LED is based on InAs/InP quantum dots emitting in the main telecom window, with a multi-photon probability of less than 10% per emission cycle and a maximum entanglement fidelity of 89%. We use this device to demonstrate GHz clocked distribution of entangled qubits over an installed fiber network between two points 4.6km apart.
Indium Arsenide (InAs) infrared photodiodes provide high quantum efficiency in the wavelength range of 1.0-3.0 μm. Planar diode configuration has been adopted to reduce surface leakage. In this work, ...new fabrication procedures for planar InAs avalanche photodiodes (APDs) are reported. Beryllium (Be) ions were implanted into InAs at a relatively low energy of 34 keV. Effects of duration of post implant annealing on the electrical characteristics of InAs APDs were investigated. It was found that a combination of post implant annealing at 500 °C for 15 min and a shallow surface etch produces planar APDs with good characteristics (room temperature dark current density of 0.52 A/cm 2 at -0.2 V and external quantum efficiency of 51% at 1520 nm at -0.3 V). These represent a 3 times reduction in dark current and 1.4 times increase in responsivity, compared to earlier Be-implanted planar InAs APDs. The APDs' avalanche gain characteristics remain similar to those from earlier reports, with a gain of 4 at a relatively low operating bias of 5 V. This suggests the potential of integrating InAs APDs with low voltage readout integrated circuits (ROIC) for development of infrared imaging arrays. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef.data.6955037).
This paper describes the design, fabrication, and performance of planar-geometry InGaAs-InP devices which were specifically developed for single-photon detection at a wavelength of 1550 nm. General ...performance issues such as dark count rate, single-photon detection efficiency, afterpulsing, and jitter are described.
We have studied twinning in GaAs nanowires grown via holes in a silica mask deposited on GaAs(111)B substrates by metal‐organic chemical vapour epitaxy without catalysts. Twins perpendicular to the ...growth direction form in the nanowires, their {111}‐type side facets leading to corrugation of their {110} side walls. The top facets are almost atomically smooth. Aberration corrected annular dark‐field scanning transmission electron microscopy reveals all twins are rotational, commencing with layers of Ga and finishing with As atoms. Energy‐loss spectroscopic profiling has shown no significant changes in the band‐gap or bulk plasmon energy at those twin boundaries, and the observed reduction of the interface plasmon energy by ∼0.13 eV is close to the detection limit of the technique, reflecting the very low energetic electronic changes related to twin formation.
We studied twinning in GaAs nanowires grown via holes in a silica mask deposited on GaAs(111)B substrates by metal‐organic chemical vapour epitaxy without catalysts. {111} twins perpendicular to the growth direction lead to corrugation of their {110} side walls. All twins are rotational, commencing with Ga and finishing with As atoms. Energy‐loss spectroscopic profiling showed no significant changes in the band‐gap or plasmon energy at those twin boundaries, reflecting the small energetic changes related to twin formation.
We explore the accessible wavelength range offered by InP AlGaInP quantum dots (QD)s grown by metal-organic vapour phase epitaxy and explain how changes in growth temperature and wafer design can be ...used to influence the transition energy of the dot states and improve the performance of edge-emitting lasers. The self assembly growth method of these structures creates a multi-modal distribution of inhomogeneously broadened dot sizes, and via the effects of state-filling, allows access to a large range of lasing wavelengths. By characterising the optical properties of these dots, we have designed and demonstrated dual-wavelength lasers which operate at various difference-wavelengths between 8 and 63 nm. We show that the nature of QDs allows the difference-wavelength to be tuned by altering the operating temperature at a rate of up to 0.12 nm K−1 and we investigate the factors affecting intensity stability of the competing modes.
Multiple layers of InP QDs, self-assembled during epitaxial growth, were incorporated into the active region of an (Al(x)Ga(1-x))(0.51)In(0.49)P based semiconductor disk laser with monolithic ...Al(x)Ga(1-x)As distributed Bragg reflector. Three gain structure samples were selected from the epitaxial wafer, bonded to single-crystal diamond heatspreaders and optically pumped at 532 nm within a high finesse external laser cavity. Laser emission with peak wavelengths at 716, 729, and 739 nm, respectively, was achieved from the three samples; the latter demonstrating tuning from 729 to 755 nm. Maximum continuous wave output power of 52 mW at 739 nm was achieved with 0.2% output coupling; the threshold and slope efficiency were 220 mW and 5.7% respectively.
Measurement and analysis of the temperature dependence of bulk and surface leakage currents in InAs avalanche photodiodes have been performed between 77 K and 290 K. At unity gain, SU-8 passivated ...InAs photodiodes have low dark current densities of 100 mA/cm 2 at 290 K and 150 nA/cm 2 at 77 K. An avalanche multiplication factor of 25 was measured at 13 V and 19.5 V at 290 K and 77 K, respectively. The photodiodes exhibit dynamic resistance-area products, calculated at 0.1 V of 34 Ω-cm 2 at 290 K and 910 MΩ-cm 2 at 77 K. Our analysis showed that between the temperatures of 200 K and 290 K, the bulk leakage current is proportional to n i 2 whereas the surface leakage current is proportional to n i from 77 K to 290 K, where n i is the intrinsic carrier concentration. The activation energies deduced were 0.36 eV and 0.18 eV suggesting diffusion dominated bulk current and generation and recombination dominated surface current.
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