Nitrogen Doping of MoSe2 by Plasma Treatment*

Ultrathin two-dimensional layered transition metal dichalcogenides (TMDs) have instigated great research interests due to their unique electrical, optical and spin-electronic properties. Similar to traditional semiconductors, doping plays a critical role in controlling TMDs’ properties and potential applications. In this work, we use molecular beam epitaxy (MBE) to fabricate monolayer Molybdenum diselenide (MoSe2) on graphene substrate. Post-growth doping is achieved by in-situ nitrogen plasma treatment of the surface. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS), we confirm the p-type doping of MoSe2 where selenium atoms are partially substituted by nitrogen atoms. Doping concentration can be controlled through the change of substrate temperature and different nitrogen plasma exposure time. The results demonstrate effective tuning of carrier density in epitaxial MoSe2 that is necessary for device applications.