Spin-dependent electron dynamics and recombination in GaAs(1-x)N(x) alloys at room temperature

We report on both experimental and theoretical study of conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs(1-x)N(x) alloys with a small nitrogen content (x = 2.1, 2.7, 3.4%). It is found that the photoluminescence circular polarization determined by the mean spin of free electrons reaches 40-45% and this giant value persists within 2 ns. Simultaneously, the total free-electron spin decays rapidly with the characteristic time ~150 ps. The results are explained by spin-dependent capture of free conduction electrons on deep paramagnetic centers resulting in dynamical polarization of bound electrons. We have developed a nonlinear theory of spin dynamics in the coupled system of spin-polarized free and localized carriers which describes the experimental dependencies, in particular, electron spin quantum beats observed in a transverse magnetic field.Comment: 5 pages, 4 figures, Submitted to JETP Letter

Electron spin quantum beats in positively charged quantum dots: nuclear field effects

We have studied the electron spin coherence in an ensemble of positively charged InAs/GaAs quantum dots. In a transverse magnetic field, we show that two main contributions must be taken into account to explain the damping of the circular polarization oscillations. The first one is due to the nuclear field fluctuations from dot to dot experienced by the electron spin. The second one is due to the dispersion of the transverse electron Lande g-factor, due to the inherent inhomogeneity of the system, and leads to a field dependent contribution to the damping. We have developed a model taking into account both contributions, which is in good agreement with the experimental data. This enables us to extract the pure contribution to dephasing due to the nuclei.Comment: 10 pages, 6 figure

Control of the Bright-Dark Exciton Splitting using Lamb Shift in a 2D Semiconductor

We have investigated the exciton fine structure in atomically thin WSe2 -based van der Waals heterostructures where the density of optical modes at the location of the semiconductor monolayer can be tuned. The energy splitting $\Delta$ between the bright and dark exciton has been measured by photoluminescence spectroscopy. We demonstrate that $\Delta$ can be tuned by a few meV, as a result of a significant Lamb shift of the optically active exciton which arises from emission and absorption of virtual photons triggered by the vacuum fluctuations of the electromagnetic field. We also measured strong variations of the bright exciton radiative linewidth, as a result of the Purcell effect. All these experimental results illustrate the strong sensitivity of the excitons to local vacuum field. We found a very good agreement with a model that demonstrates the equivalence, for our system, of a classical electrodynamical transfer matrix formalism and quantum-electrodynamical approach. The bright-dark splitting control demonstrated here should apply to any semiconductor structures

Cu(In,Ga)Se 2 mesa microdiodes: study of edge recombination and behaviour under concentrated sunlight

ABSTRACT In order to develop photovoltaic devices with increased efficiency using less rare semiconductor materials, the concentrating approach is applied on Cu(In,Ga)Se2 thin film devices. For this purpose, Cu(In,Ga)Se2 microcells with a mesa design are fabricated. The influence of the edge recombination signal is analyzed. It is found that with an appropriate etching procedure, devices as small as 50x50 µm do not experience edge recombination efficiency limitations. Under concentration, significant Voc gains are seen, leading to an absolute efficiency increase of two points per decade

Direct Observation of the Electron Spin Relaxation Induced by Nuclei in Quantum Dots

We have studied the electron spin relaxation in semiconductor InAs/GaAs quantum dots by time-resolved optical spectroscopy. The average spin polarization of the electrons in an ensemble of p-doped quantum dots decays down to 1/3 of its initial value with a characteristic time TDelta[approximate]500 ps, which is attributed to the hyperfine interaction with randomly oriented nuclear spins. We show that this efficient electron spin relaxation mechanism can be suppressed by an external magnetic field as small as 100 mT

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

We 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 PIN 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, leading to an estimation of the electrical spin injection yield of 35%. Moreover, this electroluminescence circular polarization is stable up to 70 K.Comment: 6 pages, 4 figure

Optical and recombination properties of dislocations in cast-mono silicon from short wave infrared luminescence imaging

International audienc

A Bayesian approach to luminescent down-conversion

International audienc

A Bayesian approach to luminescent down-conversion

International audienc