Simulation of charging properties of MNOS structures with embedded semiconductor nanocrystals

The effect of the oxide thickness and the depth, size and location of semiconductor nanocrystals are studied on the charging behaviour of MNOS non-volatile memory structures by the calculation of electron and hole tunneling probability to the nanocrystals or to the nitride conduction or valence band, respectively, and by the simulation of memory hysteresis behaviour. It is concluded for both MNOS structures that the optimal for charging behaviour tunnel oxide thickness is about 2 nm The presence of nanocrystals enhances the charge injection resulting in better performance, but for structures with thin tunnel oxide layer (below 3 nm) only, and if the nanocrystals are located close to the oxide/nitride interface. But in the case of very high tunneling probability, i.e., of high tunneling currents the system approaches eqilibrium and the memory behaviour collapses.