Universal In Situ Substitutional Doping of Transition Metal Dichalcogenides by Liquid-Phase Precursor-Assisted Synthesis

Abstract

Doping lies at the heart of modern semiconductor technologies. Therefore, for two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), the significance of controlled doping is no exception. Recent studies have indicated that, by substitutionally doping 2D TMDs with a judicious selection of dopants, their electrical, optical, magnetic, and catalytic properties can be effectively tuned, endowing them with great potential for various practical applications. Herein, and inspired by the sol–gel process, we report a liquid-phase precursor-assisted approach for in situ substitutional doping of monolayered TMDs and their in-plane heterostructures with tunable doping concentration. This highly reproducible route is based on the high-temperature chalcogenation of spin-coated aqueous solutions containing host and dopant precursors. The precursors are mixed homogeneously at the atomic level in the liquid phase prior to the synthesis process, thus allowing for an improved doping uniformity and controllability. We further demonstrate the incorporation of various transition metal atoms, such as iron (Fe), rhenium (Re), and vanadium (V), into the lattice of TMD monolayers to form Fe-doped WS2, Re-doped MoS2, and more complex material systems such as V-doped in-plane W x Mo1–x S2–Mo x W1–x S2 heterostructures, among others. We envisage that our developed approach is universal and could be extended to incorporate a variety of other elements into 2D TMDs and create in-plane heterointerfaces in a single step, which may enable applications such as electronics and spintronics at the 2D limit.

Scalable Substitutional Re‐Doping and its Impact on the Optical and Electronic Properties of Tungsten Diselenide

“…[ 48–50 ] As Re atoms are introduced, they break translational symmetry in the WSe 2 and increase structural disorder leading to these defect activated modes. [ 36,39,48,50 ] BEOL films exhibit similar Raman spectral trends as a function of Re concentration (Figures S6c and S7c, Supporting Information), with the addition of the A 1g 2 mode at 309 cm –1 indicating multilayer growth that is validated by AFM (Figure S2a–c, Supporting Information). Room temperature PL spectra exhibit similar dopant concentration dependence where pristine FEOL WSe 2 displays an optical band gap of 1.65 eV while Re‐WSe 2 is redshifted by 40 meV and is quenched by a factor of two (Figure 1f).…”

“…Raman spectroscopy verifies the presence of dopants (defects) in the host lattice. [ 36,39,45 ] Pristine and Re‐doped FEOL WSe 2 display peaks at 249 cm –1 and 261 cm –1 corresponding to A+E and 2 LA(M) characteristic in‐plane and out‐of‐plane Raman active modes (Figure 1e) where the absence of A 1g 2 mode further confirms the monolayer nature of the films. [ 46,47 ] As the doping concentration increases, the intensity of ZA(M) and LA(M) modes at 109 cm –1 and 128 cm –1 become prominent (Figure 1e) corresponding to the defect‐activated bands of WSe 2 .…”

“…The superior tunability of optical and transport properties as a function of doping concentration and environmental stability are demonstrated in such monolayer films. [ 36–40 ] However, tight control over the doping concentration and fundamental understanding behind homogenous dopant distribution over large areas still remain a challenge.…”

Modulating Electronic Structure of Monolayer Transition Metal Dichalcogenides by Substitutional Nb‐Doping

“…Indeed, the doping of different metal or chalcogen atoms into TMDCs during CVD growth has been reported in several systems. [23][24][25][26][27][28][29] For instance, Qin et al have grown Nb-doped WS2 by using liquid phase precursors in a two-step CVD method, while the as-grown samples have nonuniform distributions of PL intensity. [30] Li et al reported doping Se into MoS2, where Se and S are from the same group and provide limited modulation of the intrinsic properties of the TMDCs.…”

Tuning Electronic Structure of 2D In2S3 via P Doping and Size Controlling Toward Efficient Photoelectrochemical Water Oxidation

“…Substitutional doping involves the chemical bonding (usually covalent) between dopant atoms and host lattice, it is stably to tune the electrical, magnetic, and catalytic properties compared with metastable surface charge transfer processes (interstitial doping). [ 22 ] For instance, substitutional Nb doping in MoS 2 could induce a crystal conversion from 2H to 3R stacking in the layered structure attribute to the changes in d ‐electron, forming an impurity state near the host valence band and promoting the carriers’ mobility. [ 23 ] Substitutional Mo sites by Re in monolayer MoS 2 demonstrated a 0.5 eV shift of E F toward the conduction band, resulting in a degeneration of n‐type donor and reduced the sulfur deficiency simultaneously.…”