Charging Behaviour of Metal-Nitride-Oxide-Semiconductor Memory Structures with Embedded Si or Ge Nanocrystals

摘要

Charging behaviour of MNOS structures containing semiconductor nanocrytals embedded at the SiO_2/Si_3N_4 interface are studied by calculating tunneling probabilities of electrons and holes to the nanocrystals or to the conductance or valence band of the nitride layer, respectively, for structures with and without nanocrystals. The dependence of probability on the oxide thickness and electric field is discussed in terms of charge injection mechanisms. It is concluded that the optimal charging behaviour of MNOS and SONOS structures without nanocrystals can be expected for an oxide thickness of 2-3 nm. The presence of semiconductor nanocrystals at the SiO_2/Si_3N_4 interface enhances strongly the tunneling probability of electrons and holes for structures with thin oxide layers (3 nm or below) or at low electric fields, but they do not influence the charging behaviour of structures with thick oxide layers at high electric fields. The results of calculations are in agreement with the experimental results obtained on MNOS structures with Si or Ge nanocrystals.