Vapor-Solid Growth of WSe$_{2}$ Monolayers and Lateral Heterostructures

Monolayer transition metal dichalcogenides (TMDCs) are atomically thin direct-gap semiconductors that show a variety of novel electronic and optical properties such as valley-polarization of Bloch electrons, due to their symmetry and two-dimensional nature. Heterostructures and devices combining various TMDCs via vertical or lateral stacking have shown further promise for applications in nanoelectronics and nano-optics, however the need for exfoliated samples limits the investigation of such materials and devices. Here, we present the synthesis of WSe$_{2}$ monolayers and lateral WSe$_{2}$-MoSe$_{2}$ heterostructures on insulating substrates using a catalyst-free physical vapor deposition method. Monolayers and heterostructures up to 15 microns in size show high optical quality, demonstrated by a high degree of valley-polarization observed via low temperature polarization-resolved photoluminescence measurements.