Single- and narrow-line photoluminescence in a boron nitride-supported MoSe 2 /graphene heterostructure

Abstract

Heterostructures made from van der Waals (vdW) materials provide a template to investigate a wealth of proximity effects at atomically sharp two-dimensional (2D) heterointerfaces. In particular, nearfield charge and energy transfer in vdW heterostructures made from semiconducting transition metal dichalcogenides (TMD) have recently attracted interest to design model 2D "donor-acceptor" systems and new optoelectronic components. Here, using Raman scattering and photoluminescence spectroscopies, we report a comprehensive characterization of a molybedenum diselenide (MoSe 2 ) monolayer deposited onto hexagonal boron nitride (hBN) and capped by mono-and bilayer graphene. Along with the atomically flat hBN susbstrate, a single graphene epilayer is sufficient to passivate the MoSe 2 layer and provides a homogenous environment without the need for an extra capping layer. As a result, we do not observe photo-induced doping in our heterostructure and the MoSe 2 excitonic linewidth gets as narrow as 1.6 meV, approaching the homogeneous limit. The semi-metallic graphene layer neutralizes the 2D semiconductor and enables picosecond non-radiative energy transfer that quenches radiative recombination from long-lived states. Hence, emission from the neutral band edge exciton largely dominates the photoluminescence spectrum of the MoSe 2 /graphene heterostructure. Since this exciton has a picosecond radiative lifetime at low temperature, comparable with the non-radiative transfer time, its low-temperature photoluminescence is only quenched * Corresponding author.

Assessment of valley coherence in a high-quality monolayer molybdenum diselenide

“…In addition, the PL intensities of the high-quality region are about 5 times stronger than those of the lowquality sample at the same excitation power of 13 μW, demonstrating that non-radiative recombination is strongly suppressed in the high-quality sample. 20) The significant difference in FWHM and peak intensity between the two regions clearly shows that the environmental inhomogeneity due to roughness and impurities is much less in the highquality region.…”