Electron-Transport Characteristics through Aluminum Oxide (100) and (012) in a Metal–Insulator–Metal Junction System: Density Functional Theory—Nonequilibrium Green Function Approach

Al 2 O 3 is commonly used in modern electronic devices because of its good mechanical properties and excellent electrical insulating property. Although fundamental understanding of the electron transport in Al 2 O 3 is essential for its use in electronic device applications, a thorough investigation for the electron-transport mechanism has not been conducted on the structures of Al 2 O 3 , especially in nanometer-scale electronic device settings. In this work, electron transport via Al 2 O 3 for two crystallographic facets, (100) and (012), in a metal-insulator-metal junction configuration is investigated using a density functional theory-based nonequilibrium Green function method. First, it is confirmed that the transmission function, T ( E ), decreases as a function of energy in ( E - E F ) < 0 regime, which is an intuitively expected trend. On the other hand, in the ( E - E F ) > 0 regime, Al 2 O 3 (100) and Al 2 O 3 (012) show their own characteristic behaviors of T ( E ), presenting that major peaks are shifted toward lower energy levels under a finite bias voltage. Second, the overall conductance decay rates under zero bias are similar regardless of the crystallographic orientation, so that the contact interface seemingly has only a minor contribution to the overall conductance. A noteworthy feature at the finite bias condition is that the electrical current drastically increases as a function of bias potential (>0.7 V) in Al 2 O 3 (012)-based junction compared with the Al 2 O 3 (100) counterpart. It is elucidated that such a difference is due to the well-developed eigenchannels for electron transport in the Al 2 O 3 (012)-based junction. Therefore, it is evidently demonstrated that at finite bias condition, the contact interface plays a key role in determining insulating properties of Al 2 O 3 -Pt junctions.