Njg Nicolas Chauvin

Enhanced spontaneous emission in a photonic-crystal light-emitting diode

We report direct evidence of enhanced spontaneous emission in a photonic-crystal (PhC) light-emitting diode. The device consists of p-i-n heterojunction embedded in a suspended membrane, comprising a layer of self-assembled quantum dots. Current is injected laterally from the periphery to the center of the PhC. A well-isolated emission peak at 1.3μm from the PhC cavity mode is observed, and the enhancement of the spontaneous emission rate is clearly evidenced by time-resolved electroluminescence measurements, showing that our diode switches off in a time shorter than the bulk radiative and nonradiative lifetimes.

Enhanced spontaneous emission rate from single InAs quantum dots in a photonic crystal nanocavity at telecom wavelengths

The authors demonstrate coupling at 1.3μm between single InAs quantum dots (QDs) and a mode of a two dimensional photonic crystal (PhC) defect cavity with a quality factor of 15 000. By spectrally tuning the cavity mode, they induce coupling with excitonic lines. They perform a time integrated and time-resolved photoluminescence and measure an eightfold increase in the spontaneous emission rate inducing a coupling efficiency of 96%. These measurements indicate the potential of single QDs in PhC cavities as efficient single-photon emitters for fiber-based quantum information processing applications.

Growth temperature dependence of exciton lifetime in wurtzite InP nanowires grown on silicon substrates

InP nanowires grown on silicon substrate are investigated using time-resolved spectroscopy. A strong modification of the exciton lifetime is observed (from 0.11 to 1.2 ns) when the growth temperature is increased from 340 °C to 460 °C. This strong dependence is not related to the density of zinc-blende insertions in the wurtzite nanowires or to the wurtzite exciton linewidth. The excitation power dependence of the lifetime and linewidth is investigated, and these results allow us to interpret the growth temperature dependence on the lifetime as a consequence of the reduction of the surface recombination velocity with the growth temperature.

Shape-engineered epitaxial InGaAs quantum rods for laser applications

We apply artificial shape engineering of epitaxial semiconductor nanostructures to demonstrate InGaAs quantum rods (QRs), nanocandles, and quantum dots-in-rods on a GaAs substrate. The evolution of the QRs from a zero-dimensional to one-dimensional confinement is evidenced by systematically measuring the photoluminescence and photoluminescence decay as a function of the rod length. Lasers based on a three-stack QR active region are demonstrated at room temperature, validating the applicability of the QRs in the real devices.

Growth-interruption-induced low-density InAs quantum dots on GaAs

We investigate the use of growth interruption to obtain low-density InAs quantum dots (QDs) on GaAs. The process was realized by Ostwald-type ripening of a thin InAs layer. It was found that the optical properties of the QDs as a function of growth interruption strongly depend on InAs growth rate. By using this approach, a low density of QDs (4 dots/μm2) with uniform size distribution was achieved. As compared to QDs grown without growth interruption, a larger energy separation between the QD confined levels was observed, suggesting a situation closer to the ideal zero-dimensional system. Combining with an InGaAs capping layer such as In-rich QDs enable 1.3 μm emission at 4 K.

Low density 1.55 μm InAs/InGaAsP/InP (100) quantum dots enabled by an ultrathin GaAs interlayer

The authors report the formation of low density InAs/InGaAsP/InP (100) quantum dots (QDs) by metalorganic vapor phase epitaxy enabled by an ultrathin GaAs interlayer. For small InAs amount and low group-V flow rate, the QD density is reduced to below 10 QDs/μm2. Increasing the group-V flow rate slightly increases the QD density and shifts the QD emission wavelength into the 1.55 μm telecommunication region. Without GaAs interlayer, the QD density is drastically increased. This is attributed to the suppression of As/P exchange during QD growth by the GaAs interlayer avoiding the formation of excess InAs.

Lithographic and optical tuning of InGaAsP membrane photonic crystal nanocavities with embedded InAs quantum dots

Hexagonal symmetry InGaAsP membrane type cavities with embedded InAs quantum dots as active emitters were investigated by room temperature photoluminescence experiments at wavelengths near 1.50 μm. Cavities consisting of simple defects of just removing one or seven air holes were studied as well as modified cavities with additional holes decreased in size and shifted in position. The latter include the H0 cavity, in which only two adjacent holes were modified, but none removed. Low-Q cavity modes were observed for the simple cavities while high-Q modes were observed after modification of the surrounding holes. The resonant frequencies were varied over a large range of lithographic parameters both by changing the lattice spacing or the size of the modified holes. More than 15 nm reversible dynamic optical tuning of the resonance modes was observed by changing the applied laser power up to 5 mW. For thermo-optic tuning, this corresponds to a heating of up to 200 °C.

Nanophotonic technologies for single-photon devices

The progress in nanofabrication has made possible the realization of optic nanodevices able to handle single photons and to exploit the quantum nature of single-photon states. In particular, quantum cryptography (or more precisely quantum key distribution, QKD) allows unconditionally secure exchange of cryptographic keys by the transmission of optical pulses each containing no more than one photon. Additionally, the coherent control of excitonic and photonic qubits is a major step forward in the field of solid-state cavity quantum electrodynamics, with potential applications in quantum computing. Here, we describe devices for realization of single photon generation and detection based on high resolution technologies and their physical properties. Particular attention will be devoted to the description of single-quantum dot sources based on photonic crystal microcavites optically and electrically driven: the electrically driven devices is an important result towards the realization of single photon source “on demand”. A new class of single photon detectors, based on superconducting nanowires, the superconducting single-photon detectors (SSPDs) are also introduced: the fabrication techniques and the design proposed to obtain large area coverage and photon number-resolving capability are described.

Quantum integrated photonics on GaAs

We present a quantum integrated photonics platform on GaAs including waveguide single-photon sources and detectors on the same chip.

Single photon sources for quantum information applications

Efficient sources of indistinguishable single photons are a key resource for various applications in fields like quantum sensing, quantum metrology and quantum information processing. In this contribution we report on single photon generation based on III-V semiconductor quantum dots (QDs). To increase the emission efficiency of single photons, it is essential to tailor the radiative properties of the quantum dot emitters by engineering their photonic environment. We present optimized single photon emitters being based on both micropillar and photonics crystal cavities, for applications in a vertical platform and on-chip in-plane platform, respectively. Electrically driven single photon sources with self assembled semiconductor QDs embedded into GaAs/AlAs micropillar cavities emit on demand net rates of ~35 MHz single photons, thus being well exploitable in quantum key distribution systems. In order to establish also a spatially deterministic fabrication platform, position controlled quantum dots are integrated into p-i-n micropillar cavities and single photon emission of a coupled QD-micropillar diode system is observed. Efficient broadband coupling of single photons into photonic crystal waveguides provides the basis for all on-chip quantum information processing, and an according approach is reported.