Electron transport mechanism through ultrathin Al 2 O 3 films grown at low temperatures using atomic–layer deposition

Alumina (Al 2 O 3 ) films of different thicknesses have been grown at different low temperatures (100 °C–250 °C) by atomic–layer deposition on n–type Si substrate. The robustness of the Al 2 O 3 film as a barrier has been investigated based on Al/Al 2 O 3 /Si metal–insulator–semiconductor structures. The electron transport through the Al 2 O 3 layer was fitted well by the Fowler–Nordheim tunneling mechanism, from which the barrier heights (conduction band offset between Si and Al 2 O 3 ) were deduced. It was discovered that the growth temperature and film thickness both influenced the carrier transport and barrier height. The Al/Al 2 O 3 /Si structure with an ultrathin 3 nm Al 2 O 3 fabricated at 150 °C showed the largest barrier height, the lowest tunneling current density (4.9 × 10 –8 A cm −2 at 5 MV cm −1 ), and the highest breakdown field strength of 18.3 MV cm −1 . Using Au to replace Al as the electrode could suppress the tunneling current significantly. The Al 2 O 3 films were also examined by x-ray photoelectron spectroscopy to determine their chemical constituents.