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Comment: 3 pages, 2 figures, presented in ICPS-2006
Intraband transitions around 1.5 mum are studied in PbSe quantum dots at room temperature. Femtosecond pump-probe measurements reveal induced absorption by photoexcited carriers up to higher energy levels and its relaxation. A dominant decay component has a decay time of 10-40 ps, which is determined by the relaxation of carriers at the lowest absorption peak. The induced absorption is observed in a broad spectral range between 0.77 and 2.5 eV.
We study optical transitions from a periodic array of InP/InAs/InP core-multishell nanowires (CMNs) having a wurtzite crystal structure by using photoluminescence (PL) and PL excitation (PLE) spectroscopy. Observing a large Stokes shift between PL and PLE spectra, a blueshift of the PL peak with a cube-root dependence on the excitation power and a slow and nonexponential decay of PL with an effective decay time of 16 ns suggest a type-II band alignment. Band-offset calculation based on the "model-solid theory" of Van de Walle [Phys. Rev. B 39, 1871 (1989)] supports type-II band lineup if the InAs layer in the wurtzite CMNs is assumed to sustain compressive strain in all directions.
Comment: 20 pages with 9 figures, submitted to Semiconductor Science and Technology special issue on Optical Orientation
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