Substitutional doping of transition metal dichalcogenides (TMDs) may provide routes to achieving tunable p-n junctions, bandgaps, chemical sensitivity, and magnetism in these materials. In this study, we demonstrate in situ doping of monolayer molybdenum disulfide (MoS2) with manganese (Mn) via vapor phase deposition techniques. Successful incorporation of Mn in MoS2 leads to modifications of the band structure as evidenced by photoluminescence and X-ray photoelectron spectroscopy, but this is heavily dependent on the choice of substrate. We show that inert substrates (i.e., graphene) permit the incorporation of several percent Mn in MoS2, while substrates with reactive surface terminations (i.e., SiO2 and sapphire) preclude Mn incorporation and merely lead to defective MoS2. The results presented here demonstrate that tailoring the substrate surface could be the most significant factor in substitutional doping of TMDs with non-TMD elements.

Doping is the cornerstone of semiconductor technology, enabling the success of modern digital electronics. 2D transition metal dichalcogenides (TMDCs) are promising material platforms for future electronics applications where its wafer-scale synthesis and controllable doping will be a required prerequisite to drive the next technological revolution. [1-6] Successful realization of wafer-scale, electronic grade, intrinsic 2D TMDCs via common deposition methods is rapidly progressing, however, advances in scalable doping still remain in the "proof-of-concept" stage, delaying the largescale fabrication of logic circuits based on extrinsic 2D semiconductors. [7-12] Moreover, integration of 2D TMDCs with Si complementary metal-oxide-semiconductor at the back-end-of-line (BEOL) is being actively explored for diffusion barriers, liners, and thin-film-transistors to improve the overall integrated circuit performance. [13-16] However, BEOL production lines are Reliable, controlled doping of 2D transition metal dichalcogenides will enable the realization of next-generation electronic, logic-memory, and magnetic devices based on these materials. However, to date, accurate control over dopant concentration and scalability of the process remains a challenge. Here, a systematic study of scalable in situ doping of fully coalesced 2D WSe 2 films with Re atoms via metal-organic chemical vapor deposition is reported. Dopant concentrations are uniformly distributed over the substrate surface, with precisely controlled concentrations down to <0.001% Re achieved by tuning the precursor partial pressure. Moreover, the impact of doping on morphological, chemical, optical, and electronic properties of WSe 2 is elucidated with detailed experimental and theoretical examinations, confirming that the substitutional doping of Re at the W site leads to n-type behavior of WSe 2. Transport characteristics of fabricated back-gated fieldeffect-transistors are directly correlated to the dopant concentration, with degrading device performances for doping concentrations exceeding 1% of Re. The study demonstrates a viable approach to introducing true dopantlevel impurities with high precision, which can be scaled up to batch production for applications beyond digital electronics.

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