Transport mechanisms in atomic-layer-deposited Al2O3 dielectrics

Abstract

We analyze the field and temperature dependence of electron currents through atomic-layer-deposited thin (3.6–6 nm) sheets of ${\mathrm{Al}}_2{\mathrm{O}}_3$ 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 ${\mathrm{Al}}_2{\mathrm{O}}_3,$ 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 ${\mathrm{Si/Al}}_2{\mathrm{O}}_3$ conduction band offset of 2.7 eV.