Doping against the Native Propensity of MoS₂: Degenerate Hole Doping by Cation Substitution

Abstract

Layered transition metal dichalcogenides (TMDs) draw much attention as the key semiconducting material for two-dimensional electrical, optoelectronic, and spintronic devices. For most of these applications, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction. However, typically only one type of doping is stable for a particular TMD. For example, molybdenum disulfide (MoS2) is natively an n-type presumably due to omnipresent electron-donating sulfur vacancies, and stable/controllable p-type doping has not been achieved. The lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2, as well as limits carrier conduction to spin-degenerate conduction bands instead of the more interesting, spin-polarized valence bands. Traditionally, extrinsic p-type doping in TMDs has been approached with surface adsorption or intercalation of electron-accepting molecules. However, practically stable doping requires substitution of host atoms with dopants where the doping is secured by covalent bonding. In this work, we demonstrate stable p-type conduction in MoS2 by substitutional niobium (Nb) doping, leading to a degenerate hole density of ∼ 3 × 10(19) cm(-3). Structural and X-ray techniques reveal that the Nb atoms are indeed substitutionally incorporated into MoS2 by replacing the Mo cations in the host lattice. van der Waals p-n homojunctions based on vertically stacked MoS2 layers are fabricated, which enable gate-tunable current rectification. A wide range of microelectronic, optoelectronic, and spintronic devices can be envisioned from the demonstrated substitutional bipolar doping of MoS2. From the miscibility of dopants with the host, it is also expected that the synthesis technique demonstrated here can be generally extended to other TMDs for doping against their native unipolar propensity.

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.…”

Defect Structure of Localized Excitons in a WSe2 Monolayer

“…Because transition metal atoms are sandwiched between chalcogen atoms, the latter are believed to be easily removed, and chalcogen vacancies are often regarded as the most common intrinsic defect [10][11][12][13]. Accordingly, most TMD monolayers are n-type doped [3,14]. However, the WSe 2 monolayer usually shows p-type doping, either by mechanical exfoliation or chemical vapor deposition (CVD) [4,15].…”

“…However, the WSe 2 monolayer usually shows p-type doping, either by mechanical exfoliation or chemical vapor deposition (CVD) [4,15]. This p-type doping provides a natural route to fabricating a p-n junction based on lateral heterostructure [14,16]. Moreover, in conjunction with giant spin-orbit splitting and spin-valley locking at the valence band, p-type doping facilitates the manipulation of valley coherence for a more extended time to 1-10 ns [17,18], in comparison to ∼10 ps with n-type doping [19].…”

Growth and optical properties of Nb-doped WS2 monolayers

“…In the present study, Nb is selected because its atomic size is comparable to that of Mo and it is reported to generate acceptor states for some TMDCs. 16,25) Here, we report the synthesis and characterization of monolayer impurity-doped WS 2 using halide-assisted CVD.Halide-assisted CVD was used to grow large-area monolayer Nb-doped WS 2 with a crystal size of 30 µm on a SiO 2 surface. Our scanning transmission electron microscopy (STEM) observations revealed that the Nb atom was substituted at the W site at a rate of approximately 0.5%.…”