Dynamical Processes of High Density Single Excitons and Excitonic Molecules in CdSe

Abstract

To study the dynamical processes of high density single excitons and excitonic molecules in CdSe, the time dependences of M, P M and P luminescence lines and the time-resolved absorption spectra of A excitons are measured in the pico-second region at 4.2 K. The exciton absorption peak shifts to the high energy side due to the high density effect, the shift reaching the maximum at 20 ps after the pulse excitation. M line reaches the maximum at 100 ps, P M line at 200 ps and P line at 300∼350 ps. The decay constants are 100, 100 and 350 ps, respectively. The dynamical aspects of the formation of A excitons, the formation of excitonic molecules and the inelastic collisions of single excitons and excitonic molecules are discussed. It is interpreted why the use of the pico-second pulse excitation is essentially important for the realization of the Bose condensation of excitonic molecules.