A NEW METHOD FOR THE STUDY OF EXCITONS IN SEMICONDUCTORS

A new fast transient method is developed to study free and bound excit on formation and decay dynamics in semiconductors. The method uses two time-scales, slow and fast. In the slow time-scale the excitonic syst em, after its creation, is allowed to evolve freely in time, while in the fast one the detection of the state of the system due to tunnel di ssociation of excitons is performed in a fast swept electric field. Th e principle of the proposed method is demonstrated by measuring free a nd bound exciton lifetimes in the n region of silicon p+nn+ structures . Diffusion to p+n and nn+ junctions is found to limit the free-excito n lifetime at temperatures lower than 14 K, whereas at higher temperat ures exciton thermal dissociation is found to dominate.