Evidence for a conduction through shallow traps in Hf-doped Ta2O5

The influence of Hf-doping on the leakage currents and conduction mechanisms in Ta2O5 stacks is investigated. The current conduction mechanisms as well as the traps participating in them are identified by temperature dependent current-voltage measurements. A strong dependence of the dominant conduction mechanism on the doping and the layer thickness is established. Hf-doping alters substantially the dominant mechanism of conductivity in pure Ta2O5. Conduction in Hf-doped Ta2O5 is performed through shallower traps as compared to the pure Ta2O5, which results in a higher leakage current in the former stacks. A certain trap can assist in different conduction processes depending on the layer thickness and the applied field. It is found that Hf-doping passivates oxygen vacancies in Ta2O5 and the deep traps level associated with this defect is not observed in Hf-doped samples. The origin of the detected traps is also commented.