  Here, we describe synthesis of TMD crystals using a two-step flux growth
method that eliminates a major potential source of contamination. Detailed
characterization of TMDs grown by this two-step method reveals charged and
isovalent defects with densities an order of magnitude lower than in TMDs grown
by a single-step flux technique. Initial temperature-dependent electrical
transport measurements of monolayer WSe2 yield room-temperature hole mobility
above 840 cm2/Vs and low-temperature disorder-limited mobility above 44,000
cm2/Vs. Electrical transport measurements of graphene-WSe2 heterostructures
fabricated from the two-step flux grown WSe2 also show superior performance:
higher graphene mobility, lower charged impurity density, and well-resolved
integer quantum Hall states.
