H. Carrère

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

The strong light-matter interaction and the valley selective optical selection rules make monolayer (ML) MoS[subscript 2] an exciting 2D material for fundamental physics and optoelectronics applications. But, so far, optical transition linewidths even at low temperature are typically as large as a few tens of meV and contain homogeneous and inhomogeneous contributions. This prevented in-depth studies, in contrast to the better-characterized ML materials MoSe[subscript 2] and WSe[subscript 2]. In this work, we show that encapsulation of ML MoS[subscript 2] in hexagonal boron nitride can efficiently suppress the inhomogeneous contribution to the exciton linewidth, as we measure in photoluminescence and reflectivity a FWHM down to 2 meV at T = 4 K. Narrow optical transition linewidths are also observed in encapsulated WS[subscript 2], WSe[subscript 2], and MoSe[subscript 2] MLs. This indicates that surface protection and substrate flatness are key ingredients for obtaining stable, high-quality samples. Among the new possibilities offered by the well-defined optical transitions, we measure the homogeneous broadening induced by the interaction with phonons in temperature-dependent experiments. We uncover new information on spin and valley physics and present the rotation of valley coherence in applied magnetic fields perpendicular to the ML.

Room-temperature optical orientation of the exciton spin in cubic Ga N ∕ Al N quantum dots

The optical orientation of the exciton spin in an ensemble of self-organized cubic

Reduction of defect density by rapid thermal annealing in GaAsBi studied by time-resolved photoluminescence

\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{N}

Electron spin dynamics and g-factor in GaAsBi

quantum dots is studied by time-resolved photoluminescence. Under a polarized quasiresonant excitation, the luminescence linear polarization exhibits no temporal decay, even at room temperature. This demonstrates the robustness of the exciton spin polarization in these cubic nitride nanostructures, with characteristic decay times longer than

Electrical spin injection into p-doped quantum dots through a tunnel barrier

10\phantom{\rule{0.3em}{0ex}}\mathrm{ns}

Large optical bandwidth and polarization insensitive semiconductor optical amplifiers using strained InGaAsP quantum wells

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Electron spin filtering by thin GaNAs/GaAs multiquantum wells

Time-resolved photoluminescence was performed on as-grown and annealed bulk GaAsBi samples. Rapid thermal annealing was carried out at a temperature of 750 °C. With annealing, we observed a significant change in the photoluminescence decay time at low temperature and low excitation power, which is likely due to a reduction of localized states. Although the time-integrated photoluminescence intensity did not show a large variation, this enhancement was confirmed by the observed removal after annealing of the S-shape behaviour present in the as-grown sample.

Molecular beam epitaxy and properties of GaAsBi/GaAs quantum wells grown by molecular beam epitaxy: effect of thermal annealing

Electron spin dynamics in elastically strained bulk GaAsBi epilayer with 2.2% Bi concentration has been measured by time resolved photoluminescence spectroscopy. Under external transverse magnetic field, the measurement of the photoluminescence polarization oscillations resulting from the Larmor precession of electron spins yields an accurate determination of the Lande g-factor. We find that the value of g increases from −0.81 to −0.68 when the temperature rises from T = 100 K to T = 300 K. This is typically double the value of GaAs, in agreement with the larger spin-orbit interaction in GaAsBi. In this temperature range, the electron spin lifetime decreases from 370 to 100 ps.

Spin-dependent photoconductivity in nonmagnetic semiconductors at room temperature

The authors have demonstrated by electroluminescence the injection of spin polarized electrons through Co∕Al2O3∕GaAs tunnel barrier into p-doped InAs∕GaAs quantum dots embedded in a p-i-n GaAs light emitting diode. The spin relaxation processes in the p-doped quantum dots are characterized independently by optical measurements (time and polarization-resolved photoluminescence). The measured electroluminescence circular polarization is about 15% at low temperature in a 2T magnetic field, proving an efficient electrical spin injection yield in the quantum dots. Moreover, this electroluminescence circular polarization is stable up to 70K.

L-valley electron spin dynamics in GaAs

The material gain of equal width InGaAsP/InGaAsP multi–quantum well active layers is calculated solving the Luttinger–Kohn Hamiltonian, including tetragonal strain and confinement effects. The calculated optical bandwidth reaches 150 nm with a maximum polarization sensitivity of 1 dB between transverse electric (TE) and transverse magnetic (TM) emission over the −3 dB optical bandwidth. The corresponding device characterized by amplified spontaneous emission measurements shows an optical bandwidth with constant TE/TM ratio of almost 100 nm which can be improved up to 113 nm by increasing the barrier material band gap energy. Further enlargement of the optical bandwidth is expected by reducing the quantum well width.