Luminescence and Inter-Valence Band Hole Relaxation in High Density Electron-Hole Plasma in CdSe and CdS

Picosecond time-resolved spectra of the spontaneous luminescence from high density electron-hole plasma in CdSe and CdS are measured at 4.2 K under the band-to-band excitation. It is observed that two emission bands appear, which are due to the two kinds of plasmas consisting, respectively, of the A and B valence band holes. From the time changes of these two bands, it is obtained that the relaxation time of holes from the B to A valence band is ∼35 ps for CdSe and ∼55 ps for CdS. This inter-valence band relaxation of holes is caused by the acoustic phonon scattering in CdS, but in CdSe the LO-phonon scattering plays an important role in addition to the acoustic phonon scattering.