Bandgap and Defect Engineering in Atomically Thin Molybdenum Disulfide Layers Via Precise 2d Alloying Using Metal Organic Chemical Vapor Deposition for Optoelectronic Applications

Abstract

The reducing dimensionality has increased miniaturization of logic circuits in electronic and optoelectronic devices. Consequently, there was a growing need for new materials with thicknesses below 3 nm. After years of research, this need was addressed by the discovery of atomically thin layered two-dimensional (2D) materials. 2D layered materials possess a significant advantage due to their nature of dangling bond free surfaces, enabling good electrical mobility even at and#8804; 1nm thickness. This characteristic effectively minimizes leakage currents, positioning these materials as ideal candidates for extending the Moore s law. Particularly, transition metal dichalcogenides (TMDs) are notable for their atomically thin structure, intrinsic direct bandgap, pronounced spin-orbit interactions, and excellent mechanical and electronic performance. These properties making them widely used in the optoelectronics, nanoelectronics, spintronics and catalysis applications. There have been several synthesis methods such as liquid phase exfoliation, hydrothermal synthesis, and chemical vapor deposition (CVD) and metal-organic chemical vapor deposition (MOCVD). Among these, MOCVD has been explored for producing layered materials and their heterostructures. In the present thesis, we have used the gas-phase precursor assisted MOCVD to make TMDs and TMDs alloys for next generation optoelectronic applications. newlineIn the first working chapter (chapter 3), we have achieved band gap engineering via 2D alloying using MOCVD. Here, we demonstrate the growth of Mo1-xWxS2 ternary alloy monolayers and precise compositional tuning for the entire range of x from 0 to 1 using gas-phase precursor approach. Raman spectroscopy reveals that W alloying in the MoS2 lattice induces a tensile strain of approximately 0.8%. The alloying-induced tensile stress plays a key role in observing redshift in optical absorption and photoluminescence (PL) bands and resulted an unusual band gap bowing newline