Realization of electronic-grade two-dimensional transition metal dichalcogenides by thin-film deposition techniques

Defects and impurities play non-trivial roles in the functionality and device performance of two-dimensional (2D) transition metal dichalcogenides (TMD). From the optoelectronic point of view, they serve as electron scattering centers and exciton non-radiative recombination sites in 2D materials. While it is challenging to remove defects completely from monolayers, they need to be suppressed as much as possible to realize a broad range of applications in circuits, solid-state lighting, and sensing. To meet these goals, significant efforts need to be invested in understanding the growth mechanisms of 2D crystals and controlling defect formation during synthesis. In this chapter, first, we briefly discuss the challenges in synthesizing high-quality TMD and provide an overview on the thin-film deposition techniques that show a great potential for making electronic-grade 2D TMD, including powder-based and metal-organic chemical vapor deposition (CVD), as well as molecular beam epitaxy. Next, we discuss several aspects of 2D crystals growth in CVD that would impact the material quality, such as substrates, precursor dissociation dynamics, as well as nucleation and growth kinetics in detail. Finally, we review the engineering methods for controlling their heterogeneity through controlling defect type and density, heterostructure formation, and substitutional doping.