Five different models were considered, for charge transfer among coupled defect states in semiconductors, where the free-carrier density was limited by the density of unoccupied trap levels; as in the case of defect-dominated materials. In order to determine the time dependence of trap occupancy, a set of coupled differential equations was formulated that governed charge capture and emission processes for 2 defect states. A numerical solution, which assumed model parameters for traps, furnished features of the trap occupancy as a function of time. A comparison was made of the occupancy features predicted by various models. These were mainly categorized as being serial (hierarchical) or parallel charge-transfer mechanisms. The model predictions were successfully applied to the trapping kinetics of defects in heavily damaged n-type material. It was shown that, in addition to the occurrence of charge redistribution among multiple traps, the main trap in the damaged material existed in 2 metastable configurations (perhaps with negative U) and that the stable configuration referred to a mid-gap compensating center that was related to a small cluster of self-interstitials. It was noted that the present model could be extended, to more complex defect systems, by using a combination of these simple models.

Capacitance Transient Spectroscopy Models of Coupled Trapping Kinetics Among Multiple Defect States: Application to the Study of Trapping Kinetics of Defects in Heavy-Ion Damaged Silicon. P.K.Giri, Y.N.Mohapatra: Physical Review B, 2000, 62[4], 2496-504