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NRL Researchers Demystify the Nature of Metal-contacts to 2D Materials

July 21st, 2014

2d materials illustration
In a recent study, ECE researchers from the Nanoelectronics Research Lab (NRL), investigated the nature of the physical contacts between 2D TMD semiconductors and a number of metals using a novel ab-initio technique specifically designed for such 2D layered materials.

Atomically-thin, two-dimensional (2D) transition metal dichalcogenides (TMD) have emerged as promising materials for future unprecedented electronic, optoelectronic and sensor applications. TMDs offer a wide range of material types, from semiconductors to half-metals and from metals to superconductors, with variable but uniform band gaps.

Besides, these ultra-thin TMDs have inherent flexibility and transparency, rendering them attractive to display electronics. These materials additionally have pristine surfaces that can boost device performance, especially in nanoscale transistors. However, such pristine surfaces also imply that interface bonding to these materials is predominantly van der Waals (vdW) type that are inherently weak (as compared to strong covalent bonds). The vdW bonding essentially implies that there actually exists a ‘vdW gap’ at such interfaces leading to some unusual electronic behavior that had remained inexplicable till date. Moreover, the vdW type interface bonding also leads to poor contact resistances between metals and 2D TMDs.

Ensuring low-resistance metal-contacts to such semiconductors is the primary hindrance to using this technology. In a recent study, ECE researchers from the Nanoelectronics Research Lab (NRL), led by Professor Kaustav Banerjee have investigated the nature of the physical contacts between 2D TMD semiconductors (such as monolayer molybdenum disulfide) and a number of metals using a novel ab-initio technique specifically designed for such 2D layered materials. The detailed study not only provides a pathway to identify the best contact metals for these semiconductors but also reveals some new physics of the interfaces that, in turn, determine the carrier transport across such interfaces. The formalism and the results in this work provide guidelines for novel 2D semiconductor device design and fabrication, a field that is on the rise because of limitations in scaling silicon semiconductor technology.

These results have been recently published in the prestigious journal, Physical Review X, by ECE PhD student Jiahao Kang, et al. The formalism has already yielded some of the highest performance 2D TMD-transistors.

Physical Review X (APS open access journal)

Highest Performance TMD Transisitors (CoE News release)

Nanoelectronics Research Lab (NRL)