J. Barrau

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-hole liquid in GaP

Abstract Cathodoluminescence spectra of very pure GaP are recorded between 4.2 and 20 K. A new large and broad band, which rapidly grows with excitation level, is observed. This band which completely disappears near 20 K is attributed to recombination radiation of metallized droplets of electrons and holes. The critical density and the condensation enery are estimated: n c = 1.57 × 10 19 ; Φ/ k ⋍ 70 K.

Induced electrostatic confinement of the electron gas in tensile strained InGaAs/InGaAsP quantum well lasers

A new mechanism, injection induced electrostatic confinement of the electron gas, is proposed to explain the origin of the laser effect in tensile strained GaInAs/GaInAsP quantum well lasers.

Theoretical comparison of GaInAs/GaAlInAs and GaInAs/GaInAsP quantum‐well lasers

We give a detailed theoretical study of the optical gain for compressive and tensile‐strained GaInAs/GaInAlAs quantum‐well lasers, including valence‐band mixing. We demonstrate that with strained quantum wells, lower thresholds and higher differential gains are expected. We also show that these characteristics are even better than those of the most usual GaInAs/GaInAsP system. The good experimental results already obtained tend to confirm the theoretical expectations.

Effective mass-like states of the deep acceptor level of Au and Pt in silicon

Abstract In this note we report the absorption spectra associated with the acceptor level of Au and Pt in silicon. The structures observed are experimental evidence of effective mass-like states related with these centres. A symmetry lower than Td is suggested for both centres.

Hole spin relaxation in intrinsic quantum wells

Abstract We observe a fast decay of the photoluminescence intensity in intrinsic quantum wells (QW), for excitation energies above the QW gap. This fast decay is interpreted as the result of the transfer of excitons from optically active states (angular momentum J = 1) to non-optically active ( J = 2) ones; the transfer is driven by the spin relaxation of holes. This observation leads us to propose a method to measure directly the hole spin relaxation time in intrinsic quantum wells, independently of any other spin-flip mechanism. We determine then the dependence of the hole spin relaxation time versus the photogeneration energy in various lattice matched GaAs AlGaAs and strained GaInAs GaAs QW. The obtained results are essential in order to interpret the spin relaxation mechanism of holes in intrinsic quantum wells.

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.

Enhanced exciton blue shift in spin polarized dense exciton system in quantum wells

Abstract We have performed a dynamical study of the blue shift and splitting of the exciton line in dense polarized exciton systems in quantum wells. The strong initial polarization of the excitons allows the separate evaluation of the strong repulsive part (due to the Pauli exclusion principle) and the small attractive part (due to the long range Coulomb effects) of the collective interactions between the excitons.

Photoluminescence from gold centre in silicon

Abstract A sharp line structure attributable to ṕhonon assisted radiative emission has been observed in the low temperature photoluminescence spectra from deep centres in bulk samples of gold-doped silicon. The entire luminescence band which peaks near 0.78 eV is attributed to transitions of conduction electrons towards the gold-related donor level.

The zero-phonon luminescence from gold in silicon

Abstract The zero-phonon luminescence associated with the 0.78 eV band from gold in silicon [Mazzaschi et al. (1981)] is observed at high resolution. It corresponds to an internal transition at the defect. The interpretation as a radiative transition from shallow “hydrogen-like” states towards the deep donor state is coherent with the known experimental results. It would imply a reduced symmetry of the site.