Novel doping alternatives for single-layer transition metal dichalcogenides

Abstract

Successful doping of single-layer transition metal dichalcogenides (TMDs) remains a formidable barrier to their incorporation into a range of technologies. We use density functional theory to study doping of molybdenum and tungsten dichalcogenides with a large fraction of the periodic table. An automated analysis of the energetics, atomic and electronic structure of thousands of calculations results in insightful trends across the periodic table and points out promising dopants to be pursued experimentally. Beyond previously studied cases, our predictions suggest promising substitutional dopants that result in p-type transport and reveal interesting physics behind the substitution of the metal site. Doping with early transition metals (TMs) leads to tensile strain and a significant reduction in the bandgap. The bandgap increases and strain is reduced as the d-states are filled into the mid TMs; these trends reverse are we move into the late TMs. Additionally, the Fermi energy increases monotonously as the d-shell is filled from the early to mid TMs and we observe few to no gap states indicating the possibility of both p-(early TMs) and n-(mid TMs) type doping. Quite surprisingly, the simulations indicate the possibility of interstitial doping of TMDs; the energetics reveal that a significant number of dopants, increasing in number from molybdenum disulfide to diselenide and to ditelluride, favor the interstitial sites over adsorbed ones. Furthermore, calculations of the activation energy associated with capturing the dopants into the interstitial site indicate that the process is kinetically possible. This suggets that interstitial impurities in TMDs are more common than thought to date and we propose a series of potential interstitial dopants for TMDs relevant for application in nanoelectronics based on a detailed analysis of the predicted electronic structures.where E(nM X 2 + D I ) is the energy of the TMD sample with n formula units including an interstitial dopant. We note that the formation energy for an adsorbed atom is defined following Eq. 2 as well. It is clear from Eqs. 1 and 2 that the formation energies depend on the chemical potential of the species involved, which are determined by growth conditions. The chemical potentials for the metal and chalcogen atoms are typically considered between two limits: metal rich and chalcogen rich. Under metal-rich conditions {µ M −rich M ,µ M −rich X }, the chemical potential of the metal is set by its ground state crystal structure and that for the chalcogen is set such that the TMD is in equilibrium with the metal source.In chalcogen-rich conditions {µ X−rich M ,µ X−rich X }, the chemical potential of the chalcogen is obtained from

Coexistence of valley polarization and Chern insulating states in MoS2 monolayers with n-p codoping

“…For the 3 × 3 supercell MoS 2 ML with one Mo substituted by Nb atom (Nb 1 ), the Nb tends to substitute the Mo atom instead of the S atom for both rich Mo and S cases, consistent with the tendency reported in previous researches [16][17][18][19][20] . The Nb 1 substituted MoS 2 ML is also proved to be dynamically stable (without imaginary frequency) through the density functional perturbation theory (DFPT) 21 .…”

Molecular chemistry approaches for tuning the properties of two-dimensional transition metal dichalcogenides

“…1,[51][52][53] Whereas a lot of progress has been reported and reviewed on the synthesis of 2D-TMD sheets, 16,50,[54][55][56] seemingly, relatively less work has been focused on the second critical aspect, which is nevertheless a veritable bottleneck to the incorporation of 2D TMDs in (opto)electronic technologies. 1,[51][52][53] Achieving a systematic control over charge-carrier doping is essential for minimizing detrimental Schottky barriers at metalsemiconductor interfaces, 57 as well as for manufacturing p-n junctions and transistors with reproducible electrical characteristics, which are crucial requirements for the production of complementary-logic devices and circuits. 58 Conventional doping techniques, such as ion implantation and dopant diffusion, are extremely challenging to be implemented in combination with 2D TMDs, since damages/defects induced by such processes in ultrathin crystals can have drastic effects on their structural and electrical properties.…”

Tungsten disulfide-based nanomaterials for energy conversion and storage

“…For example, Singh et al [78] revealed that substitutional doping of 3d transition-metal atoms (Ti, V, Cr, Mn, Fe, Co, and Ni) at the W site is feasible by calculating the binding energy based on the density functional theory. Furthermore, Onofrio et al [79] used DFT to investigate WS 2 with a large section of the periodic table. The calculation results proved that doping with early transition metals (TMs) results in the tensile strain of WS 2 and a significant reduction of the band gap.…”