Novel Synthesis Methods for 2D Transition Metal Dichalcogenides And Their Heterostructures

Among all the 2D materials, transition metal dichalcogenides (TMDs : MX₂; where M being Mo, W and X being S, Se, Te) are prominent class of nanostructures which have remarkable properties due to their direct bandgap (visible to IR) semiconducting nature, interlayer exciton interactions by type-II band alignment, strong spin-orbit coupling and easily accessible electronic valley degree of freedom. These semiconducting monolayers can be stacked or stitched in to vertical or lateral heterojunctions to form van der Waals heterostructures for atomically thin p-n junction diodes and valleytronic devices. However, the fully controlled growth of monolayer TMDs and fabrication of heterostructures with atomically clean and sharp interfaces are still in infant stage due to the limitations in available growth methods and complex growth mechanisms.

We present the results of in-house developed, affordable and reliable novel growth methods for the growth of scalable and device compatible atomically thin 2D TMDs. The commercially available oxide and volatile metal precursors are optimized by tuning the growth parameters to grow both monolayer and heterostructured 2D TMDCs in bottom–up approach, using chemical vapor deposition (CVD) technique. The chemical composition, crystal structure, number of layers, and bandgap estimation by Raman and photoluminescence spectroscopies confirmed the high optical and device quality mono- and heterostructured van der Waal layers of as grown samples. Almost 100 % efficient transfer of as grown layers to random substrates is achieved by adopting the etching free and surface energy assisted transfer method, for both optical and electrical device studies. By understanding the growth mechanism, we developed the growth recipes for successful in situ doping and alloying of atomically thin nanostructures.