Picosecond Relaxation Processes of High Density Electron–Hole Plasma in CdSe

Abstract

AbstractPicosecond time‐resolved spectra of the spontaneous luminescence from high density electron‐hole plasma in CdSe are measured at 4.2 K with changing excitation photon energy in the vicinity of the bandgap energy by using tunable picosecond pulses. Spectra observed are analyzed, and the electron‐hole concentration and effective carrier temperature of the plasma are obtained as a function of excitation photon energy as well as of the delay time. It is found that both the electron‐hole concentration and effective carrier temperature decrease remarkably for the first 150 ps after pulse excitation, and that thereafter the concentration and temperature remain almost unchanged at ≈3 × 1017 cm−3 and ≈20 K, respectively, until to the very late stage down to the 800 ps delay time. It is concluded that the effective carrier temperature does not fall below ≈20 K in spite of decreasing the excess energy given to the carriers at the instance of pulse excitation by means of changing the excitation photon energy. It is sure that there exists a process which makes the plasma hot. The phonon‐assisted Auger process is suggested as such a process.