A new method for the study of excitons in semiconductors

A new fast transient method is developed to study free and bound exciton formation and decay dynamics in semiconductors. The method uses two time-scales, slow and fast. In the slow time-scale the excitonic system, 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 dissociation of excitons is performed in a fast swept electric field. The principle of the proposed method is demonstrated by measuring free and 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-exciton lifetime at temperatures lower than 14 K, whereas at higher temperatures exciton thermal dissociation is found to dominate.