Effect of glass electronic states on carrier dynamics in semiconductor quantum-dot structures

Ultrafast carrier dynamics of CdS0.4Se0.6 nanocrystals excited at various photon energies are investigated by femtosecond nonlinear transmission spectroscopy. As the excitation photon energy is decreased, the enhanced bleaching and its rapid recovery of 1S(e)-1S(3/2)(h) state are observed with the development of an additional 1S(e)-2S(3/2)(h) bleaching and a spectrally broad photoinduced absorption. We have found that the electron trapping into the glass electronic states has significant effect on the carrier dynamics by reducing the carrier densities in both confined and surface states as the photoexcitation energy increases.