ABSTRACT

The ability to reduce the size of the basic switch in computers, the transistor, is being seriously challenged. Materials that have been used for decades, such as silicon, are anticipated to soon reach the limit of their performance. This will impact applications where reduced power is needed, along with high speed switching, such as portable electronics and cell phones, as well as larger power intensive operations, like data storage and server centers. The collaborative international team of researchers in this program will focus on determining the feasibility of using the ultimate limit for such switches: atomically-thin, two-dimensional (2D) layers. The materials to be studied, called "transition metal dichalcogenides," are unique when produced in atomically thin sheets, and exhibit promising properties that may enable efficient low power, high performance computing. A key property that will be studied is the surface and interfaces of these materials as they are combined to form the transistor, and how the chemical and physical properties of these interfaces impact and improve the transistor electrical switching behavior. The research results could enable the possibility of reducing the power consumption associated with the broad spectrum of electronic devices, which drive the information and communication age. This will be good for society in terms of extended battery life in portable devices and also good for the environment in terms of reducing the total electrical energy consumed by information and communication technologies. The project, entitled "Understanding the Nature of Interfaces in Two-Dimensional Electronic Devices (UNITE)," brings together leading researchers from the USA, the Republic of Ireland and Northern Ireland, each funded by their respective government agencies through the US Ireland R&D Partnership Program. The project will provide training to five graduate students in the USA and Ireland, and will include student exchanges between the Institutes providing a broader scientific and cultural experience for the graduate students supported through the project.

The UNITE project will investigate the synthesis, device fabrication and characterization of 2D transition metal dichalcogenides semiconductors for applications in low voltage tunnel field effect transistors. We will explore two separate routes to large area synthesis through van der Waals epitaxy and atomic layer deposition. In parallel, characterization and understanding of the surfaces and interfacial regions between commercially available bulk crystals and technologically relevant contacts and insulators will be conducted. This will be accomplished using a combination of in-situ and ex-situ characterization covering questions such as: how can 2D semiconductor surfaces be functionalized to allow uniform and continuous oxide thin films to be formed by atomic layer deposition; can capacitance-voltage based metrology be applied to metal-oxide-semiconductor systems on 2D semiconductor surfaces; what is the nature of conduction for metal contacts on 2D semiconductors; and how are the atomic scale electrical properties related to larger area contacts' It is noted that the development of growth methods for large area substrates will not only demonstrate the potential to move 2D semiconductor based transistors from research to production, but will also provide a source of technologically interesting 2D semiconductor materials for basic study which are not commonly available through geological sources. Finally, the growth and characterization studies will be applied to the fabrication of a tunnel field effect transistor based on two dimensional semiconductor heterostructures. If the UNITE team can successfully understand the issues relating to large area 2D synthesis, uniform insulator deposition, ohmic contact formation, and charge transport in single or few layer 2D semiconductors, this knowledge will be relevant to a range of potential device architectures.

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