P-type Doping in Large-Area Monolayer MoS₂ by Chemical Vapor Deposition

Abstract

Molybdenum disulfide (MoS 2 ) with excellent properties has been widely reported in recent years. However, it is a great challenge to achieve p-type conductivity in MoS 2 because of its native stubborn n-type conductivity. Substitutional transition metal doping has been proved to be an effective approach to tune their intrinsic properties and enhance device performance. Herein, we report the growth of Nb-doping large-area monolayer MoS 2 by a one-step salt-assisted chemical vapor deposition method. Electrical measurements indicate that Nb doping suppresses ntype conductivity in MoS 2 and shows an ambipolar transport behavior after annealing under the sulfur atmosphere, which highlights the p-type doping effect via Nb, corresponding to the density functional theory calculations with Fermi-level shifting to valence band maximum. This work provides a promising approach of two-dimensional materials in electronic and optoelectronic applications.

Substitutional doping in 2D transition metal dichalcogenides

“…Such a spatial variation was also observed in V-doped WS2 [85]. Nb dopants introduce an acceptor state in MoS2 above a doping density of 8% [29,32,79]. Similarly, DFT calculations show that 6.25% doping of Nb in WS2 does not introduce midgap states but brings the Fermi energy below the VBM to maintain the charge neutrality of the system [23].…”

“…Since the physical properties of TMDs are strongly influenced by chalcogen vacancies that are present in high concentrations (10 13 to 10 14 cm −2 ) [142,143], intentionally introduced impurities may indirectly modulate the carrier density of the host material by altering the stability of such vacancy defects [66,93]. Nevertheless, systems such as V-doped WSe2 and V-doped WS2 have so far shown a clear sign of expected hole doping, indicating sufficiently small impurity ionization energy [44,86], unlike the case of Nb-doped MoS2 monolayer where p-type conduction enhancement is often marginal [79], unless an alloying impurity density is reached [67]. Identifying the suitable elements for versatile carrier modulation for different host material remains a crucial task.…”

“…Jin et al [80] and Suh et al [82] observed enhanced electrical conductivity and concluded that the p-type doping is degenerate at Nb content of 1.4% and 0.5%, respectively, based on suppressed gate modulation. Other groups observed reduced normal state conductance [79,83]. Qin et al [83] observed a progressive positive shift of the FET threshold voltage and the emergence of a hole branch at Nb content of > 2.5% (Fig.…”

“…Nb is a common p-type dopant for TMDs [23,79,80]. Nb-doped WS2 and MoS2 have been grown by powder CVD using NbCl5 [23,80], Nb metal [81] and Nb2O5 [79] as the Nb source, by CVT using Nb metal [82], and by MOCVD using NbCl5 [67], with achieved doping densities between 1% and 19% [23,67,80,81]. Qin et al [83] showed that the doping density in their Nb-doped WS2 grown using liquid phase mixtures decreases from the center to the edge region of the triangular crystals by as much as 50% [84] (Fig.…”

Ambipolar 2D Semiconductors and Emerging Device Applications

“…Through optimizing the growth conditions, single crystal 2D WSe 2 could reach up to 165 µm wide. [ 90 ] Besides WSe 2 , many efforts have been made on other ambipolar 2D materials like MoS 2 , [ 91–94 ] WS 2 , [ 95 ] MoSe 2 , [ 96–100 ] and even ternary compounds. [ 101 ] Both of MoS 2 and MoSe 2 have been achieved scalable growth.…”