Efficient doping of TMDs using NH₃ plasma treatment

The precise control of dopant concentration and distribution in two-dimensional materials (2D), e.g. transition metal dichalcogenides (TMDs), is a major problem on the way to their successful application in modern nanoelectronics. Efficient doping can be achieved by substituting chalcogenide atoms with group V or VII atoms, intercalations or electrostatic doping. In the present work, both the optical and electrical properties of mechanically exfoliated 2D TMDs have been modified using NH₃ plasma treatment for 10 s followed by short-time annealing. After plasma treatment, the TMDs flakes were investigated by photoluminescence (PL) and Raman spectroscopies and current-voltage (I-V) characteristics. After NH₃ plasma treatment, the PL-peak intensity of the MoSe₂ monolayer degrades and shifts towards lower energy (higher wavelength) due to hydrogen doping. Annealing after plasma treatment releases hydrogen and the PL emission returns to normal. The same has been observed in Raman spectra. H-doping causes a shift of the main phonon modes due to the phonon-plasmon coupling, i.e. Fano effect. The I-V characteristics also clearly confirm the efficient hydrogen doping of the MoSe₂ monolayer. This work shows new insights into controllable doping in 2D materials.