Electron transport mechanism through ultrathin Al 2 O 3 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.