Charge Storage Behavior of Ion Beam Synthesized Au Nanocrystals

Studies of semiconductor nanocrystals (NC’s) in the MOS gate oxide received much interest due to their potential application in non-volatile memory devices. However, the detailed charge storage mechanism is still under discussion. Defect-based charge trapping at NC surfaces is hard to distinguish from storage in the conduction band of NC’s. For metal NC’s in SiO2 the situation is different. Charge traps at the Au/SiO2 interface are assumed to be negligible at first sight. In this contribution, Au NC’s serve as a model system for the charge storage phenomena in NC containing gate oxides with a thickness of less than 40 nm. For the present study, Au NC’s were synthesized by low-energy ion implantation followed by annealing. The formation of well-separated NCs (4..5 nm diameter) were observed by X-TEM studies. Additionally, a zone denuded of NC’s forms at the interface. Thus, the formed NC-layer has the right distance from the Si/SiO2 interface for charging by direct electron tunneling. On prepared MOS capacitor structures, charge storage behavior was successfully demonstrated by capacitance-voltage measurements.