Transition-metal dichalcogenides (TMDs) have recently emerged as a class of two-dimensional materials relevant for use in electronic devices. Similar to graphene, these materials form layered crystals which lack out-of-plane bonding, allowing exfoliation to create atomically thin flakes of the materials on a substrate. Unlike graphene, however, TMDs have an intrinsic bandgap, making these materials more appealing for digital applications. Further, the electronic and optical properties of TMDs vary with the number of layers, with significant widening of the bandgap and a transition from an indirect to a direct bandgap in the monolayer limit.
2D vertical heterostructures composed of TMDs have a number of interesting applications, including digital logic, analog communications systems, and optical applications. However, the quality of currently available synthetic materials is not sufficient to realize many of these applications. Further, the impact of defects and layer-to-layer interactions on the electronic behavior of heterostructures is not well understood.
To further the understanding of TMD behavior, Nanolab is interested in demonstrating synthesis techniques for TMDs that are compatible with conventional CMOS processing. These processes require wafer-scale uniform growth of films. To achieve this, we are exploring various synthesis techniques for TMDs, including chemical vapor deposition (CVD), thin film alloying, and vapor phase epitaxy, using a combination of equipment available through the Georgia Tech IEN and the Georgia Tech Research Institute. In particular, we have demonstrated large-area synthesis techniques for MoS2 and WSe2 with excellent uniformity and are actively pursuing growth of a wide variety of other 2D materials. Building on this synthesis work, we are interested in combining these synthesis techniques to create heterostructures of 2D materials and explore the relationship between synthesis techniques, defect structures of the materials, interface quality, and device behavior. By understanding how to control the behavior of these heterostructures, we hope to unlock some of the interesting applications of 2D materials, including steep-slope transistors and resonant tunneling.
Highlighted Publications:
- “Band structure effects on resonant tunneling in III-V quantum wells versus two-dimensional vertical heterostructures”
M. Campbell, A. Tarasov, C. A. Joiner, W. J. Ready, and E. M Vogel, Journal of Applied Physics (2016) - “Field-Effect Transistors based on Wafer-Scale, Highly Uniform Few-Layer P-type WSe2”
M. Campbell, A. Tarasov, C. A. Joiner, M.-Y. Tsai, G. Pavlidis, S. Graham, W. J. Ready, and E. M. Vogel, Nanoscale (2016) - “Enhanced Resonant Tunneling in Symmetric2D Semiconductor Vertical Heterostructure Transistors”
M. Campbell, A. Tarasov, C. A. Joiner, W. J. Ready, and E.M. Vogel, ACS Nano (2015) - “Graphene-Molybdenum Disulfide-Graphene Tunneling Junctions with Large-area Synthesized Materials”
A. Joiner, P. M. Campbell, A. Tarasov, B. R. Beatty, C. J. Perini, M.-Y. Tsai, W. J. Ready, and E. M. Vogel, ACS Applied Materials & Interfaces (2016) - “Controlled Doping of Large-Area Trilayer MoS2 with Molecular Reductants and Oxidants”
Tarasov, S. Zhang, M.Y.-Tsai, P. M. Campbell, S. Graham, S. Barlow, S. R. Marder, and E. M. Vogel, Advanced Materials (2015) - “Highly Uniform Trilayer Molybdenum Disulfide for Wafer-Scale Device Fabrication”
Tarasov, P. M. Campbell, M.-Y. Tsai, Z. R. Hesabi, J. Feirer, S. Graham, W.J. Ready, and E.M. Vogel, Advanced Functional Materials (2014).
