Article,
Single-Electron Charging and Discharging Analyses in Ge-Nanocrystal Memories
IEEE TRANSACTIONS ON ELECTRON DEVICES, 58 (2): 376-383 (2011)
DOI: 10.1109/TED.2010.2091959
Abstract
The transient charging/discharging of electrons in Ge-nanocrystal (NC)
memories are measured by a pump-and-probe method that allows keeping
track of the number of electrons per NC. The experiments are simulated
with a quantum kinetic mechanical model based on the density-functional
theory, which can describe the NCs' charging state. In the transient
charging, electrons are captured faster than predicted by simulations.
This was attributed to the presence of defects in the NC surface, action
of which is twofold: 1) The incoming electrons are captured by NC states
and are quickly thermalized down to the surface traps. 2) Those traps
enlarge the spatial distribution of the confined wave functions,
increasing their penetration in the tunneling oxide and the incoming
transition rates. As for the discharging, the calculations and
experiments agree until there are only few electrons left per NC. Then,
the out tunneling becomes slower than predicted by calculations. The
remaining electrons are confined in trap states with energies located in
the NC bandgap, and they have to be thermally excited to NC states and
to tunnel out to the substrate.
