Laser annealing for Large Excitonic Reflectivity from MoSe2 grown by Chemical Vapor Deposition

We present data of a laser annealing procedure which drastically improves the quality of suspended monolayers of chemical vapor deposition grown MoSe2. Annealing with a green laser locally heats the suspended flake, which both removes contaminants and reduces strain gradients. At 4 K, we observe linewidths as narrow as 3.5 meV (1.6 nm) full width at half maximum for both photoluminescence and reflection. Large peak reflectances up to 47% are also observed. These values are comparable to those of the highest quality hexagonal boron nitride encapsulated samples. We demonstrate that this laser annealing process can yield spatially homogeneous samples where the length scale of the homogeneity is limited primarily by the size of the suspended area. Annealed regions are very stable, exhibiting negligible deterioration over 24 h at cryogenic temperatures. The annealing method is also very repeatable.