M. Brousseau

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.

Hole spin relaxation in n-modulation doped quantum wells

Abstract The hole spin relaxation in n-modulation doped quantum wells has been investigated as a function of the laser excitation energy and excitation intensity. We demonstrate for the first time that the heavy hole spin flip time is a very strong decreasing function of these two parameters. We present a simple interpretation which assigns these dependences to the carriers temperature variation.

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.

Dynamical equilibrium between excitons and free carriers in quantum wells

Abstract We have investigated the exciton and free carrier populations dynamics in quantum wells by low temperature time-resolved photoluminescence spectroscopy. When the excitation energy is set above the free carrier quantum well gap, excitons are formed from random binding of electrons and holes. On the basis of this bimolecular formation process, we show that a 2D mass action law, describing the coexistence of free carriers and excitons, explains the time evolution of the exciton photoluminescence linewidth. This demonstrates the existence of a thermodynamic equilibrium between excitons and free carriers at each time delay following the excitation. The consequence is a very short exciton formation time (≲ 10 ps) in the density range investigated (10 9 – 10 10 cm −2 ), implying a bimolecular formation coefficient γ higher than 14 cm 2 s −1 .

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.

Studies of defects introduced by electron irradiation at 4.2 °K in p‐silicon by thermally stimulated capacitance technique

Point defects, introduced at 4.2 °K in p‐type silicon by 1.5‐MeV electron irradiation, are studied by means of the thermally stimulated capacitance technique. Electronic states associated with the vacancy and the divacancy are observed, which enables us to study their correlated annealing. The respective donor energy levels, hole thermal emission rates, and annihilation activation energies are measured.

Time resolved spectroscopy of CdSe, using monopulsed picosecond excitation

Abstract We have studied at 4.2 K, the time resolved luminescence of CdSe platelets, using two photons absorption and monopulsed excitation. From the analysis of the A-LO excitonic lineshape, we have obtained the relaxation kinetics of the exciton temperature during the first 1.3 nsec. We deduce the loss rate d /dt of the mean exciton energy. We report also at higher excitation, the occurence of new lines in the luminescence spectrum.

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.

Spot size effects in picosecond luminescence experiments

Abstract We have studied, with picosecond technics, the luminescence dependence on the laser spot size for highly excited CdSe and CdS. We have also performed space and time resolved experiments in order to estimate the density distribution within the excited region. We discuss the dilemma: plasma expansion or stimulation effects.