Two-dimensional TMDs have unique optoelectronic properties, including enhanced room temperature excitonic luminescence (excitons are Coulomb-bound electron-hole pairs), high optical absorption per layer and optical memories spanning a large dynamic range.

Chemical Vapor Deposition (CVD) offers a synthetic route towards scalable generation of TMDs, and to modify defect density for optical memory tuning and neuromorphic computing. Even though CVD has been extensively used to synthesize semiconducting transition metal dichalcogenides (TMDs), the critical importance of choice of substrates as well as growth promoters is poorly understood. We explore the role of oxygen mixed with carrier gas during the CVD process (O-CVD). A controlled amount of O2 during growth can improve the quality of the sample by passivation of vacancies that usually occur at high process temperatures in conventional CVD, as well as influence the nucleation density. We also study the impact of oxygen as a tuning knob for the optical and electrical properties of 2D TMDs.

Useful references: Keerthana S Kumar et al, “Understanding the interplay of defects, oxygen, and strain in 2D materials for next-generation optoelectronics”, 2D Mater. 11 045003 (2024)

Additionally, the ability to synthesize large-area, single crystalline layers is a prerequisite for realizing the full potential of TMDs in cutting-edge technologies. The crystalline orientation of as- grown layers can be controlled by surface symmetry of a suitable mono- crystalline substrate, such as sapphire (Al2O3). This phenomenon is called “epitaxy”. We study the factors affecting the epitaxial growth of monolayer TMDs via CVD, such as growth conditions, nucleation density and substrate symmetry. We also aim to probe the substrate morphology-induced modifications of the optoelectronic properties of the epitaxially grown monolayers.

Useful references: Li et al., “Epitaxial growth of wafer-scale molybdenum disulfide semiconductor single crystals on sapphire”, Nature Nanotechnology, 16, 1201– 1207 (2021)