Electron transport mechanism through ultrathin Al2O3 films grown at low temperatures using atomic–layer deposition
Alumina (Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt;) films of different thicknesses have been grown at different low temperatures (100–250 alt;supagt;oalt;/supagt;C) by atomic–layer deposition on n–type Si substrate. The robustness of the Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt; film as a barrier has been investigated based on Al/Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt;/Si metal–insulator–semiconductor structures. The electron transport through the Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt; layer was fitted well by the Fowler–Nordheim tunneling mechanism, from which the barrier heights (conduction band offset between Si and Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt;) were deduced. It was discovered that the growth temperature and film thickness both influenced the carrier transport and barrier height. The Al/Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt;/Si structure with an ultrathin 3 nm Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt; fabricated at 150 alt;supagt;oalt;/supagt;C showed the largest barrier height, the lowest tunneling current density (4.9 × 10alt;supagt;–8alt;/supagt; A/cmalt;supagt;2alt;/supagt; at 5 MV/cm), and the highest breakdown field strength of 18 MV/cm. Using Au to replace Al as the electrode could suppress the tunneling current significantly. The Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt; films were also examined by X–ray photoelectron spectroscopy to determine their chemical constituents.