Covalent Nitrogen Doping and Compressive Strain in MoS₂ by Remote N₂ Plasma Exposure

Abstract

Controllable doping of two-dimensional materials is highly desired for ideal device performance in both hetero- and p-n homojunctions. Herein, we propose an effective strategy for doping of MoS2 with nitrogen through a remote N2 plasma surface treatment. By monitoring the surface chemistry of MoS2 upon N2 plasma exposure using in situ X-ray photoelectron spectroscopy, we identified the presence of covalently bonded nitrogen in MoS2, where substitution of the chalcogen sulfur by nitrogen is determined as the doping mechanism. Furthermore, the electrical characterization demonstrates that p-type doping of MoS2 is achieved by nitrogen doping, which is in agreement with theoretical predictions. Notably, we found that the presence of nitrogen can induce compressive strain in the MoS2 structure, which represents the first evidence of strain induced by substitutional doping in a transition metal dichalcogenide material. Finally, our first principle calculations support the experimental demonstration of such strain, and a correlation between nitrogen doping concentration and compressive strain in MoS2 is elucidated.

Phosphorous doped p-type MoS2 polycrystalline thin films via direct sulfurization of Mo film

“…Currently, there is argument on the conductivity of undoped MoS 2 . The majority of recent studies of undoped MoS 2 conductivity report n-type behavior, 2,8,9,[12][13][14][37][38][39][40] and the previous studies revealed that the Fermi-level tends to be pinned at charge neutrality level or sulfur vacancy level which is located below the conduction band edge, so electrons are injected, thus making MoS 2 conductivity mostly n-type. 37 Furthermore, MoS 2 transistors are essentially Schottky barrier transistors, and thus the charge injection from the source electrode degrades the transistor output.…”

“…The blue shift of the E 1 2g mode with respect to the undoped MoS 2 suggests that the type of strain generated due to the presence of Mo-P bonding is compressive. 14 Azcatl et al 14 first reported that strain induced by a single atom dopant in MoS 2 treated with a remote plasma N 2 exposure could be verified by observing its Raman spectrum, and they have confirmed that the presence of nitrogen can induce compressive strain in the MoS 2 structure. The calculated Mo-S bond length is 2.411 Å, the Mo-P bond length of 2.410 Å is slightly shorter than that of Mo-S, 31 which suggests a contraction of the MoS 2 lattice due to the introduction of phosphorus as a dopant.…”

“…However, particularly this point has been challenging to realize using MoS 2 due to its natural tendency for unipolar (n-type) transport. 12 Even though there have been various reports on p-type doping for MoS 2 , such as nitrogen plasma-assisted doping on exfoliated MoS 2 , [13][14][15] phosphorous ion implantation, 12 a substitutional doping using niobium (Nb) in bulk MoS 2 , 16,17 respectively, such efforts are limited to nano-or micro-scale flakes of MoS 2 obtained from bulk materials. Therefore considerable efforts are required for scalable synthesis of p-type MoS 2 film to realize practical applications.…”

Introducing Magnetism into 2D Nonmagnetic Inorganic Layered Crystals: A Brief Review from First-Principles Aspects

“…The substitutional doping of ReS 2 was achieved with Mo as the dopant, but the monolayer has not yet been magnetized due to the isoelectronic structures of Mo and Re [117]. Similarly, the magnetism is still lacking on the covalent N-doped MoS 2 monolayer [118]. 3d TM dopants were also incorporated into MoS 2 single crystals [119].…”

Relation between film thickness and surface doping of MoS2 based field effect transistors

“…According to the type of doping required, dopants with excess or deficit of electrons can be employed. 6,[8][9][10][11] However, replacing the atoms induces damage to the MoS 2 lattice, causing an increase in carrier scattering and hence reduced mobility. On the other hand, in the case of surface doping, the dopant is physically adsorbed on the surface of the film without disrupting the MoS 2 lattice.…”