Vapor-transport growth of high optical quality WSe2 monolayers

Abstract

Monolayer transition metal dichalcogenides are atomically thin direct-gap semiconductors that show a variety of novel electronic and optical properties with an optically accessible valley degree of freedom. While they are ideal materials for developing optical-driven valleytronics, the restrictions of exfoliated samples have limited exploration of their potential. Here, we present a physical vapor transport growth method for triangular WSe2 sheets of up to 30 μm in edge length on insulating SiO2 substrates. Characterization using atomic force microscopy and optical microscopy reveals that they are uniform, monolayer crystals. Low temperature photoluminescence shows well resolved and electrically tunable excitonic features similar to those in exfoliated samples, with substantial valley polarization and valley coherence. The monolayers grown using this method are therefore of high enough optical quality for routine use in the investigation of optoelectronics and valleytronics.

Ultra‐Long Lifetimes of Single Quantum Emitters in Monolayer WSe2/hBN Heterostructures

“…The sample investigated was based on CVD grown monolayer WSe 2 . As‐grown WSe 2 monolayers were transferred off of their SiO 2 growth substrate and encapsulated by few‐nanometer hBN flakes using an all‐dry viscoelastic stamping procedure to preserve their optical quality (see Figure a).…”

Ultrafast Self-Limited Growth of Strictly Monolayer WSe2Crystals

“…Thus the formation of WSe 2 is a thermodynamically dominant surface reaction process and subsequently tends to aggregate into amorphous structures instead of crystals with high crystalline, which is aggravated by their extremely strong surface tension and poor wettability over the substrate. Several approaches had been developed to fabricate WSe 2 crystals by utilizing low pressure or employing high‐vapor‐pressure precursors to improve the mass‐transport process so as to weaken the influence of the thermodynamic factor and optimize the deposition efficiency . However, the presence of multilayers is still unavoidable and the root cause lies in the lack of significantly energetically favorable competition between layer accumulation and size expansion, which cannot be solved by only adjusting the dynamic mass transport process.…”

Monolayer Tungsten Disulfide (WS2) via Chlorine‐Driven Chemical Vapor Transport

“…By heating the material under vacuum, a vapor is produced and the desired mono to few layers can be deposited on a cooler substrate. PVD has been used to successfully grow some monolayer TMD crystals, but a variety of limitations exist. For example, it is challenging to grow TMDs that lack a sufficient vapor pressure for transport at high growth temperatures under vacuum.…”