Femtosecond time-resolved electron-hole dynamics and radiative transitionsin the double-layer quantum well of the CdS/(HgS)(2)/CdS quantum-dot-quantum-well nanoparticle - art. no. 035317

The femtosecond time-resolved exciton dynamics of the CdS/(HgS)(2)/CdS quan tum-dot-quantum-well system (QDQW), which contains a double-layer HgS QW, w as investigated and compared to the dynamics of the QDQW system with a sing le-layer HgS QW. The femtosecond hole-burning technique allowed us to resol ve the energy of the different optically allowed excitonic states involved in the ultrafast relaxation pathway. The experimentally obtained exciton en ergies were in excellent agreement with the previously theoretically predic ted values. The femtosecond time-resolved pump-probe measurements reveal a fast relaxation component of similar to5 ps at wavelengths less than or equ al to 700 nm. At longer wavelengths, a slow decay component is found, which increases in decay time with increasing wavelength. The fast decay compone nt (5 ps) was attributed to an energy relaxation process of the two 1P(e)-1 P(h) exciton states, whereas the slow one was assigned to the decay of the dim 1S(e)-1S(3/2) state. The inhomogeneously broadened absorption band and the wide distribution of decay times in the low-energy region give strong e vidence for a broad inhomogeneous energy distribution of the lowest energet ic 1S(e)-1S(3/2) dim state. This is discussed in terms of the morphological structure of the quantum well.