Picosecond studies of highly excited CdS

Results on picosecond luminescence and excite-and-probe transmission as well as transient grating measurements for highly excited CdS measured at a bath temperature of 5 K will be presented. The luminescence and optical gain both due to electron-hole plasma and excitonic molecule recombination are observed. The electron-hole plasma decays very fast by bimolecular recombination of electrons and holes in the plasma and diffusion of the carrier toward the low density regions, and transforms into excitons and excitonic molecules within 100–200 ps. The possibility of electron-hole liquid formation is definitely excluded. The exciton and excitonic molecule decay rather slowly and govern the optical properties for times longer than 200 ps.