Non-Technical: Controlling electrical transport in semiconductors by impurity doping has enabled an entire generation of technology. As device length scales shrink, pushing the limits of silicon technology, new atomically thin semi-conducting materials such as two-dimensional transition metal dichalcogenides are emerging as a potential replacement to silicon. While doping control has been perfected for silicon technology over many decades, controlled synthesis and doping strategies for atomically thin transition metal dichalcogenides are still in their infancy. In this project, the investigators propose to demonstrate a stable doping strategy for such materials which involves substitution of the transition metal atom by an impurity metal. The investigators propose to show how both hole and electron doping is possible using such an approach. This work could enable controllable and stable doping of transition metal dichalcogenide nanosheets to tune their carrier type and density, thereby paving the way for next generation electronic and optoelectronic devices constructed from atomically-thin semiconductors. To integrate research and teaching, the investigators propose specially designed interactive learning modules (virtual labs) which will be integrated into the curriculum at the Rensselaer Polytechnic Institute. Outreach includes demonstrations of the interactive modules to students and teachers from local area high schools; this will help to popularize science and attract underrepresented groups to careers in science and engineering.
There are very few reports of direct substitution (doping) of transition metal atoms in atomically-thin transition metal dichalcogenides. This is likely due to the fact that transition metal atoms are far more stable than chalcogens and hence much harder to replace. However initial results by the investigators indicate that large-area (in situ) transition metal doping for monolayer transition metal dichalcogenides is indeed possible during the chemical vapor deposition growth process. In this project, the investigators propose first-principles density functional theory calculations over a wide range of doping concentrations to understand how the semiconducting and optoelectronic properties of such materials are affected by transition metal doping. On the experimental side, the investigators propose to demonstrate that the doping can be systematically tuned over a wide range. Variable temperature electronic transport measurements, using a back gated field-effect transistor configuration will be performed to establish how the material's electronic properties are influenced by doping. Further, photoluminescence and differential reflectance spectroscopy over a wide range of temperatures and dopant concentrations will be carried out to understand how doping affects the optoelectronic properties of the material. The project will culminate in a technology demonstration featuring an atomically sharp p-n junction device. To accomplish the above tasks, the investigators have assembled an interdisciplinary team with complementary expertise. Collaboration between experimentalists and a theorist will enable the team to develop an in-depth understanding of the underlying physics and make rapid progress towards controllably and stably doping atomically-thin transition metal dichalcogenide materials.