Capacitance transient spectroscopy models of coupled trapping kinetics among multiple defect states: Application to the study of trapping kinetics ofdefects in heavy-ion-damaged silicon

We have considered live different models of charge transfer among coupled d efect states in semiconductors where the free-carrier density is Limited by the density of unoccupied trap levels, as in the case of defect-dominated materials. To determine the time dependence of the trap occupancy features, we formulate a set of coupled differential equations that govern charge ca pture and emission processes for two defect states. A numerical solution as suming model parameters for traps provides features of the trap occupancy a s a function of time. A critical comparison is made in occupancy features f or different models, primarily categorized as serial (hierarchical) and par allel mechanisms of charge transfer. The model predictions are successfully applied to a study of trapping kinetics of defects observed in heavily dam aged n-type silicon. We show that, in addition to the occurrence of charge redistribution among multiple traps, the major trap in the damaged silicon exists in two metastable configurations, perhaps with negative U (Hubbard c orrelation energy), and the stable configuration refers to a midgap compens ating center related to a small cluster of self-interstitials. The applicab ility of our model simulations can be extended to more complex defect syste ms using a combination of these simple models.