Boosting and Balancing Electron and Hole Mobility in Single- and Bilayer WSe₂ Devices via Tailored Molecular Functionalization

Abstract

WSe2 is a layered ambipolar semiconductor enabling hole and electron transport, which renders it a suitable active component for logic circuitry. However, solid-state devices based on singleand bi-layer WSe2 typically exhibit unipolar transport and poor electrical performances when conventional SiO2 dielectric and Au electrodes are used. Here, we show that silane-containing functional molecules form ordered monolayers on the top of the WSe2 surface, thereby boosting its electrical performance in single-and bi-layer field-effect transistors. In particular, by employing SiO2 dielectric substrates and top Au electrodes, we measure unipolar mobility as high as µh = 150 cm 2 V-1 s-1 and µe = 17.9 cm 2 V-1 s-1 in WSe2 single-layer devices when ad hoc molecular monolayers are chosen. Additionally, by asymmetric double-side functionalization with two different molecules, we provide opposite polarity to the top and bottom layer of bi-layer WSe2, demonstrating nearly balanced ambipolarity at the bi-layer limit. Our results indicate that the controlled functionalization of the two sides of WSe2 mono-and bilayer flakes with highly ordered molecular monolayers offers the possibility to simultaneously achieve energy level engineering and defect functionalization, representing a path towards the deterministic control over charge transport in 2D materials.

Near‐Unity Molecular Doping Efficiency in Monolayer MoS2

“…This strategy has been successfully demonstrated in carbon nanotubes, graphene, and transition metal dichalcogenides for both electron and hole doping to generate materials with a wide range of doping levels. [ 3–21 ] For MoS 2 in particular, [ 22 ] the two‐electron reduced form of benzyl viologen (BV 0 ) can dope MoS 2 degenerately with an electron sheet density of ≈1.2 × 10 13 cm −2 .…”

Molecular Functionalization of Chemically Active Defects in WSe2 for Enhanced Opto‐Electronics

“…[ 7 ] Compared with the extensively studied MoS 2 devices, the transport behavior of monolayer WSe 2 FETs shows stronger dependence on the metal contact and the surrounding dielectric environment, exhibiting different transport modes (unipolar/ambipolar) and varying dominant carriers (electron/hole). [ 8–10 ] In addition, large discrepancies of carrier mobility in 2D transistors between theoretical predictions and experimental results can be found in literature. [ 11–14 ] These all inspire researchers to study the impact of intrinsic and extrinsic defects in 2D materials on their charge transport properties in transistors.…”

Recent progresses of NMOS and CMOS logic functions based on two-dimensional semiconductors

“…Furthermore, the profuse functional groups in organic materials can tailor the charge transfer with 2D host materials. Among those organic molecule's functional groups, -SH, -OH, -NH2, and benzyl as n-type dopants donate electrons to 2D host materials [84,[86][87][88], and -CF3 is likely to induce hole-doping because of high electronegativity of the F element [87,89]. Based on this SCTD approaches, various organic chemical materials have been used to dope 2D semiconductors, including octadecyltrichlorosilane (OTS, n-dope [90]), 3-aminopropyltriethoxysilane (APTES, n-dope [91]), tetrafluoro-tetracyanoquinodimethane (F4TCNQ, p-dope [92]), and triphenylphosphine (PPh3, n-dope [93]), are also summarized in Table 1.…”