A roadmap for electronic grade 2D materials

Abstract

Since their modern debut in 2004, 2-dimensional (2D) materials continue to exhibit scientific and industrial promise, providing a broad materials platform for scientific investigation, and development of nano-and atomic-scale devices. A significant focus of the last decade's research in this field has been 2D semiconductors, whose electronic properties can be tuned through manipulation of dimensionality, substrate engineering, strain, and doping. 1-8 2D semiconductors such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) have dominated recent interest for potential integration in electronic technologies, due to their intrinsic and tunable properties, atomic-scale thicknesses, and relative ease of stacking to create new and custom structures. However, to go "beyond the bench", advances in large-scale, 2D layer synthesis and engineering must lead to "exfoliation-quality" 2D layers at the wafer scale. This roadmap aims to address this grand challenge by identifying key technology drivers where 2D layers can have an impact, and to discuss synthesis and layer engineering for the realization of electronic-grade, 2D materials. We focus on three fundamental areas of research that must be heavily pursued in both experiment and computation to achieve high-quality materials for electronic and optoelectronic applications. The document is organized as follows:

Low-temperature synthesis of 2D anisotropic MoTe2 using a high-pressure soft sputtering technique

“…and heated up to a high temperature in the presence of H 2 S or S 2 gas. 20 This method enables the synthesis of MoS 2 , WS 2 , and others, 19,21,22 but lacks precise control of gas precursor concentrations and ow, as well as lm thickness, and defect concentrations, and is thus unsuitable for producing device-quality lms needed in large-scale manufacturing. The powder-CVD synthesis of MoTe 2 requires much higher processing temperatures ($800 C) for crystallization to occur.…”

Caveats in obtaining high-quality 2D materials and property characterization

“…quickly advanced beyond micrometer-sized flakes of 2D layers produced by the scotch-tape method and toward the realization of continuous films over large-area substrates (up to 300 mm diameter SiO 2 /silicon) [4,5,6,7,8,9], all enabled by simple vapor deposition techniques [10]. The most rudimentary of these techniques utilizes a tube furnace-based approach, including solid source precursors and, more recently, nucleation or seeding agents that can yield 2D films over large areas [4,11,12,13].…”

Molecular Beam Epitaxy Scalable Growth of Wafer‐Scale Continuous Semiconducting Monolayer MoTe2 on Inert Amorphous Dielectrics

“…Transition metal dichalcogenides (TMDs) (MX 2 , M = Mo or W, X = S, Se, or Te) have attracted intense interest for developing ultrascaled electronics and optoelectronics by virtue of their attractive 2D layered structures and unique physical properties that are absent in their bulk counterparts . Monolayer semiconducting TMDs show sizable direct bandgaps, quantum confinement effects, large exciton binding energies and effective valley polarizations, which unveils widespread applications in field‐effect transistors (FETs), photodetectors, light‐emitting diodes, pumped lasers, solar cells, and valleytronic devices .…”

“…Monolayer semiconducting TMDs show sizable direct bandgaps, quantum confinement effects, large exciton binding energies and effective valley polarizations, which unveils widespread applications in field‐effect transistors (FETs), photodetectors, light‐emitting diodes, pumped lasers, solar cells, and valleytronic devices . More excitingly, their 2D structures offer superior electrostatic controllability and exemptible short‐channel effects, rendering TMDs promising candidates for future sub‐10 nm complimentary metal‐oxide‐semiconductor (CMOS) devices . The applications of exfoliated TMD flakes in building high‐performance prototypes of electronics, photonics, and optoelectronics have already been demonstrated .…”

“…The high nuclei ripening rate over lateral growth rate generally favors thick island tellurides growth rather than that of continuous monolayers . In contrast, fully coalesced monolayer sulfides and selenides films can be favorably fabricated by optimizing the kinetic and/or thermodynamic rates of nucleation and crystal growth . Therefore, the controllable synthesis of large‐area uniform monolayer MoTe 2 is still technologically challenging, while highly desirable for device applications.…”