We present time-resolved photoluminescence measurements performed on an ensemble of InAs quantum dots
with density of 1011 dots/cm2 and ground state transition energies centered at 1.216 eV. The wavelength of the
100fs excitation pulse was tuned through the ground (excited) state transitions, resulting in resonant (optical
phonon assisted) photoluminescence (PL). The PL was detected with its polarization both parallel with and
perpendicular to the excitation polarization (along one of the crystal's cleave axes). The decay of the PL was
time-resolved with a streak camera in the interval 1.5 - 3ns to avoid scattered laser light. A strong polarization
dependence was observed. Considerable amount of the resonant fluorescence signal and even of the non-resonant
PL signatures remained linearly polarized on a nanosecond time scale. A phenomenological rate equation analysis
is made.
The optical emission and gain properties of Ga(AsSb) quantum-islands are investigate. These islands form during growth
in a self-organized process in a series of Ga(AsSb)/GaAs/(AlGa)As heterostructures, resulting in an additional in-plane
hole confinement of several hundreds of meV. The shape of the in-plane confinement potential is nearly parabolic and thus
yields almost equidistant hole energy levels. Transmission electron microscopy reveals that the quantum islands are 100nm
in diameter and exhibit an in-plane variation of the Sb concentration of more than 30 %. Up to seven bound hole states
are observed in the photoluminescence spectra. Time-resolved photoluminescence data are shown as function of excitation
density, lattice temperature, and excitation photon energy and reveal fast carrier capture into and relaxation within the
quantum islands. Furthermore, the optical gain is measured using the variable stripe-length method and the advantages of
such structures as active laser material are discussed.
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