Electron transport mechanism through ultrathin Al2O3 films grown at low temperatures using atomic–layer deposition

Alumina (Al2O3) films of different thicknesses have been grown at different low temperatures (100–250 °C) by atomic–layer deposition on n–type Si substrate. The robustness of the Al2O3 film as a barrier has been investigated based on Al/Al2O3/Si metal–insulator–semiconductor structures. The electron transport through the Al2O3 layer was fitted well by the Fowler–Nordheim tunneling mechanism, from which the barrier heights (conduction band offset between Si and Al2O3) were deduced. It was discovered that the growth temperature and film thickness both influenced the carrier transport and barrier height. The Al/Al2O3/Si structure with an ultrathin 3 nm Al2O3 fabricated at 150 °C showed the largest barrier height, the lowest tunneling current density (4.9 × 10–8 A/cm2 at 5 MV/cm), and the highest breakdown field strength of 18.3 MV/cm. Using Au to replace Al as the electrode could suppress the tunneling current significantly. The Al2O3 films were also examined by X–ray photoelectron spectroscopy to determine their chemical constituents.