We have studied the photoluminescence from type-II GaSb/GaAs self-assembled quantum dots in magnetic fields up to 50 T. Our results show that at low laser power, electrons are more weakly bound to the dots than to the wetting layer, but that at high laser power, the situation is reversed. We attribute this effect to an enhanced Coulomb interaction between a single electron and dots that are multiply charged with holes.

We study nanograin size confinement effects, and the effect of the increase of local temperature on the first-order Raman spectrum in silicon nanogranular films obtained by cluster deposition. The local temperature was monitored by measuring the Stokes/antiStokes peak ratio with the laser power up to ϳ20 kW/cm 2. We find large energy shifts, up to 30 cm Ϫ1 , and broadenings, up to 20 cm Ϫ1 , of the Raman-active mode, which we attribute to both laser heating and confinement effects. The phonon softening and phonon linewidth are calculated using a phenomenological model which takes into account disorder effects through the breakdown of the kϭ0 Raman-scattering selection rule, and also anharmonicity, which is incorporated through the threeand four-phonon decay processes. Very good agreement with experimental data is obtained for calculated spectra with nanograin sizes of about 10 nm, and with an increase in the anisotropy constants with respect to those of bulk silicon.

We report photoluminescence (PL) measurements on self-assembled GaSb/ GaAs quantum dots. As the laser excitation is increased from very low levels, the PL shows a strong red shift, and then a blue shift, such that it presents a U-shaped curve. Raising the temperature causes a large ͑Ͻ100 meV͒ blue shift of the PL, and shifts the minimum of the PL energy versus laser excitation curve to higher laser powers. Applying a magnetic field at lasers powers Ӷ1 W cm −2 red shifts the PL energy. We explain these effects by population or depopulation of dots that are filled in the dark with holes supplied by carbon acceptors.

No abstract