In many device modeling and simulations, it is commonly assumed that the barrier height and the effective electron mass are constant regardless of the oxide thickness and the interfacial nitrogen concentration for nitrided oxides. In this work, we have examined the dependence of barrier height and effective electron mass on gate oxide thickness and nitrogen concentration at SiOxNy/Si interface. From the measurement of the direct tunneling and Fowler-Nordheim (FN) tunneling currents we have been able to determine both the barrier height and the effective electron mass without assuming a value for either the effective electron mass or the barrier height. It is observed that with the interfacial nitrogen concentration increased, the barrier height decreases, and the effective electron mass increases. On the other hand, it is also observed that the reduction in the gate oxide thickness leads to a decrease of the barrier height but an increase in the effective electron mass. These results are explained using the electronic structures of SiO2 and SiOxNy.
In this work, we have found that the charging of nc-Si in a thin gate oxide can induce a reduction in the total gate oxide capacitance. The capacitance can approach zero value if all the nanocrystals are charged up. The reduction of the gate oxide capacitance is attributed to the premature breakdown in the gate oxide due to the charging up in the nanocrystals, as the reduction of the gate oxide capacitance corresponds to a large decrease in the gate oxide leakage current. Here the breakdown caused by the charging in the nanocrystals is somewhat similar to the soft or hard breakdown in pure SiO2 thin films that are related to the charge trapping in the oxide film. The breakdown caused by the charging in the nanocrystals is found to be fully recoverable under ultra-violet (UV) light illumination for 5 minutes and a thermal annealing at temperature of 100°C for 10 minutes. The reduction and recovery of the capacitance due to the charging and discharging in the nanocrystals is explained with an equivalent circuit model.