Statistics of deep-level amphoteric traps in insulators and at interfaces

Abstract

An analysis is presented on the statistics of deep-level amphoteric traps in insulators and at interfaces (insulator boundaries) in terms of the occupancy functions for neutral and ionized trapping centers as a function of free carrier injection and spatial distribution of centers. Amphoteric traps are postulated for bulk insulator traps, such as silicon nitride in nonvolatile, erase-write, semiconductor memory structures. In addition, amphoteric traps may be observed at interfacial boundaries, such as SiO2-Si3N4, SiO2-Al2O3, Si-SiO2, and insulator-liquid with site bonding. Under free carrier electron injection we find the characteristic trapped-charge centroid movement decreases for small values of Rn=σ+n/σ0n, the ratio of capture cross sections for ionized to neutral trapping centers. These results reduce to Arnett’s treatment for single-occupancy trapping centers (Rn≫1). Efficient conversion of positive (unoccupied) to negative (double-occupancy) charged centers occurs under free carrier electron injection with Rn≂1. An analogous situation exists for the reverse operation, namely, conversion of negative to positive charged centers under free carrier hole injection.