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

AlO 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 AlO 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 AlO, especially in nanometer-scale electronic device settings. In this work, electron transport via AlO 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, (), decreases as a function of energy in ( - ) < 0 regime, which is an intuitively expected trend. On the other hand, in the ( - ) > 0 regime, AlO(100) and AlO(012) show their own characteristic behaviors of (), 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 AlO(012)-based junction compared with the AlO(100) counterpart. It is elucidated that such a difference is due to the well-developed eigenchannels for electron transport in the AlO(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 AlO-Pt junctions.