Tunneling current at the interface of silicon and silicon dioxide partly embedded with silicon nanocrystals in metal oxide semiconductor structures

Abstract

A model has been developed to study the tunneling current at the interface of silicon and silicon dioxide (SiO2), partly pure and partly embedded with the silicon nanocrystallites (nc-Si) in a metal oxide semiconductor structure. Two types of tunneling, high field (Fowler-Nordheim) and low field (direct), have been investigated, in particular, their dependence on the barrier height, the effective mass, and the dielectric constant. The presence of the nanocrystallites confined in a narrow layer in the gate dielectric enhances the Fowler-Nordheim (FN) tunneling due to the barrier lowering. The gate current voltage characteristic shows that the total current is a combination of both direct and FN tunneling currents. It is also observed that the onset voltage of the FN tunneling is somewhat reduced in the present case due to the SiO2 layer embedded with the silicon nanocrystallites, compared to the pure SiO2 layer without any nanocrystallites present. The FN tunneling current has also been found to be enhanced with the increase of the volume fraction and the crystallite size of the nanocrystalline silicon.