P. Le Jeune

Anisotropy of the electron Landé g factor in quantum wells

The pulsation measurement of electron spin quantum beats by time resolved photoluminescence in a magnetic field perpendicular or at to the growth axis yields the transverse and longitudinal components of the electron Lande g factor in GaAs quantum wells (QW). The anisotropy of the g factor is thus determined as a function of the well width. No difference is found between the components of the g factor parallel and perpendicular to the growth axis for a 12 nm wide QW, whereas a clear anisotropy is measured for narrower QW.

Electron Spin Beats in InGaAs/GaAs Quantum Dots

Time-resolved picosecond spectroscopy is used for the first time to study optical orientation and spin dynamics of carriers in self-organized In(Ga)As/GaAs quantum-dot (QD) arrays. Optical orientation of carriers created by 1.2 ps light pulses, both in the GaAs matrix and wetting layer, and captured by QDs is found to last a few hundreds of picosecond. The saturation of electron ground state at high-excitation-light intensity leads to electron polarization in excited states close to 100% and to its vanishing in ground state. Electron-spin quantum beats in a transverse magnetic field are observed for the first time in semiconductor QDs. We thus determine the quasi-zero-dimensional electron g factor in In0.5Ga0.5As/GaAs QDs to be: |g⊥|=0.27±0.03.

Determination of the sign of the conduction-electron g factor in semiconductor quantum wells by means of the Hanle effect and spin-quantum-beat techniques

A method of measuring the sign of the conduction-electron g factor in semiconductor quantum-wells is proposed, based on determination of the sense of electron-spin Larmor precession by the Hanle effect or spin-quantum-beat techniques under oblique incidence of pump light on the sample, with the luminescence detected at an angle to the pump beam. This method has been used to measure the sign of the transverse electronic g-factor component in GaAs/Al0.3Ga0.7As quantum-wells of various widths. It has been shown experimentally that the average spin of electrons photocreated in quantum-wells may not coincide with the pump light direction. Expressions for the oscillations of the luminescence circular polarization in the spin-quantum-beat regime and in the Hanle effect have been obtained, taking into account the electron spin relaxation anisotropy.

Strain optimization for high differential gain and low current operation in 1.55 μm InGaAs/InGaAsP quantum well lasers

The effect of strain on threshold current and differential gain in 1.55 μm InGaAs/InGaAsP quantum well lasers is reviewed. A constant decrease in the threshold current with increasing stress is predicted if a conventional model of Auger recombination is used. We propose a more realistic model based on an accurate method for the derivation of the Auger recombination rate in quantum wells. Unlike the conventional theory, a realistic valence band structure along with Fermi–Dirac statistics and analytic expressions of the transition matrix element for both bound–bound and bound-unbound Auger processes are employed. Contrary to conventional modeling, computation results show an optimal compressive strain of approximately 1% that minimizes the threshold current and maximizes the differential gain. These results are in good agreement with the experimental results reported in the literature.

Theoretical study of Auger effect in 1.5 μm quantum-well lasers

A new methodology for the derivation of the Auger recombination rate in quantum wells is presented. An expression of the Auger recombination rate is given, taking into account a realistic valence band structure, the Fermi–Dirac statistics, and the analytic expressions of the transition matrix element for both bound-bound and bound-unbound Auger processes. Using this method, distributions of carriers involved in bound-bound and bound-unbound recombination processes are carried out. The bound-unbound recombination mechanism is identified as a significant contribution to the Auger total current density. Because the transition matrix element is found to be a significantly increasing function of the quantum-well width, our computations show that the Auger effect is expected to be enhanced in narrow wells. Subsequently, strain dependence of the Auger current density is analyzed. It is found that the Auger effect is reduced by strain in some cases but it is equally shown that this is not a general rule as it dep...

Coherent Manipulation of the Exciton Orientation in Quantum‐Wells

We demonstrate that the optical orientation of excitons can be coherently controlled and directly observed in a resonant time-resolved photoluminescence experiment. The optical dephasing time of excitons, their longitudinal and transverse spin relaxation times, and their radiative lifetime, are measured with strictly the same experimental conditions. This technique, which relies on the linear response of the crystal, is used to investigate the spin-dependent exciton–exciton interactions.

Quantum coherence dynamics of 2D excitons

Optical and quantum interferences are distinguished in a coherent control experiment which relies on the linear optical response of the crystal.