Ultrafast dynamics of valence holes in photo-excited semiconductors studied by femtosecond time-resolved photoelectron spectroscopy

点击翻译按钮获取中文摘要

Ultrafast dynamics of photo-generated non-equilibrium carriers (excited electrons in the conduction band and holes in the valence band) in typical semiconductors has been studied by femtosecond time-resolved photoelectron spectroscopy. We successfully observed time-evolution of carrier populations, in the energy (E) and momentum (k) space, and determined the fundamental scattering processes that govern the carrier relaxation. We have determined directly the rates of intervalley scatterings and carrier thermalization times of excited electrons. Also, in order to derive direct information on hole-dynamics in valence band, we have developed a new technique, one-photon photoelectron differential spectroscopy, where the difference in the photoelectron images with and without pump excitation is acquired. By using this technique, we have obtained first the direct information on ultrafast relaxation in silicons of photo-generated holes and the transition between bulk and surface states.