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 °C–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 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 Al₂O₃ films were also examined by x-ray photoelectron spectroscopy to determine their chemical constituents. (paper)