Transport mechanisms in atomic-layer-deposited Al2O3 dielectrics

We analyze the field and temperature dependence of electron currents through atomic-layer-deposited thin (3.6-6 nm) sheets of Al2O3 which were annealed above the crystallization temperature. On the basis of electrical characterization and numerical simulation that includes trap-assisted transport as well as the band bending in the contact regions, we have identified three characteristic field regions in which the currents are dominated by elastic trap-assisted tunneling, Frenkel-Poole hopping, or Fowler-Nordheim tunneling. We find that the Frenkel-Poole traps lie in a narrow band about 1.2 eV below the conduction band minimum of Al2O3, whereas the energetic distribution of the elastic traps is broad and has a tail that reaches far into the band gap. The numerical results are compatible with a Si/Al2O3 conduction band offset of 2.7 eV. (C) 2004 American Institute of Physics.