This presentation will highlight the nucleation and evolution of TMDs, specifically MoSe2 , MoS2 & WSe2. Studies were performed on substrates such as SiO2/Si, Epitaxial Graphene(EG)/SiC and III-Nitrides. Lateral growth was observed on several samples, and corresponding optical as well as compositional variation across the step-bunched terrace widths of the templated layers of EG/6H-SiC (0001) was observed. µ-Raman spectroscopy, AFM and Photoluminescence (PL) will be used to extract composition, presence, layer thickness, surface morphology variations and optical band structures of the heterostructure. The synthesis process of TMDs on a template of monolayer EG/6H-SiC (0001) was carried out in horizontal CVD reactor at 700°C – 950˚C for 10 - 30 min in a flowing UHP Ar/H2 ambient of 80/20 sccm and 10-100 mbar. The initial Raman Spectroscopy characterization of MoSe2/EG/6H-SiC heterostructure shows a strong planar and axial acoustic active modes of the TMDs material system. In addition, the out-of-plane vibrations of Se atoms and in-plane vibrational modes of Mo and Se atoms observed. Initial partial syntheses of WSe2 show random formation of W particle-nucleation sites on the terrace of EG template. The surface density of the nucleation sites was ~ 3.0 x109cm-2. The RMS roughness of 0.5 x 0.5 μm2 AFM scans of the terraced WSe2 structures was ~ 0.213 nm. The Raman spectroscopy shows a convoluted A1’ & E’ signature peak at 220cm-1, which contrast previous reported modes that assumes degeneracy at 248-251cm-1. Raman spectroscopy indicates that graphene is present (2D and D peaks) with minimal disruption to the lattice. PL of WSe2 /EG/6H-SiC (0001) show the presence of two (A and B) low exciton peak energy at 1.68eV and 2.05eV.
The successful synthesis of wafer-scale formation of WSe2 or MoSe2 heterostructures offers the opportunity for a number of applications with significant advantages over the conventional top-down exfoliation and transfer process.
For instance, direct growth of 2D heterostructures on multifarious substrate eliminates the need to transfer the 2D material to another substrate, consequently reducing segregation of impurities at the interfaces thereby mitigation against the short channel effects in nano-device structures.