Highly Stable and Tunable Chemical Doping of Multilayer WS₂ Field Effect Transistor: Reduction in Contact Resistance

Abstract

The development of low resistance contacts to 2D transition-metal dichalcogenides (TMDs) is still a big challenge for the future generation field effect transistors (FETs) and optoelectronic devices. Here, we report a chemical doping technique to achieve low contact resistance by keeping the intrinsic properties of few layers WS2. The transfer length method has been used to investigate the effect of chemical doping on contact resistance. After doping, the contact resistance (Rc) of multilayer (ML) WS2 has been reduced to 0.9 kΩ·μm. The significant reduction of the Rc is mainly due to the high electron doping density, thus a reduction in Schottky barrier height, which limits the device performance. The threshold voltage of ML-WS2 FETs confirms a negative shift upon the chemical doping, as further confirmed from the positions of E(1)2g and A1g peaks in Raman spectra. The n-doped samples possess a high drain current of 65 μA/μm, with an on/off ratio of 1.05 × 10(6) and a field effect mobility of 34.7 cm(2)/(V·s) at room temperature. Furthermore, the photoelectric properties of doped WS2 flakes were also measured under deep ultraviolet light. The potential of using LiF doping in contact engineering of TMDs opens new ways to improve the device performance.

Doping, Contact and Interface Engineering of Two‐Dimensional Layered Transition Metal Dichalcogenides Transistors

“…The ions with different electron affinity can act as electron donors and acceptors. Khalil et al reported the doping of WS 2 by LiF . The F − ions has extra electrons.…”

Surface Charge Transfer Doping of Low‐Dimensional Nanostructures toward High‐Performance Nanodevices

“…The electronic and optical properties of unipolar n‐type WS 2 can also be manipulated by the SCTD method. Khalil et al reported a downshift of the Raman peak for WS 2 by using LiF as an n‐type dopant . The light emission of WS 2 could be remarkably enhanced after the decoration of F4‐TCNQ molecules, due to the depletion of electrons in the WS 2 upon doping .…”

Crystalline tungsten sulfide thin films by atomic layer deposition and mild annealing

“…8,9 In particular, during the last few years intense attention has been given to the broad and versatile group of transition metal dichalcogenides (TMDCs), which includes metals and semimetals as well as semiconductors with band gaps varying from less than 1 to nearly 3 eV. 2,3,10,11 The properties of TMDCs can be further tailored by controlling their thickness, 12,13 surface functionalization, 14 strain, 15,16 doping and alloying, 17,18 and creating heterostructures with other 2D materials. 8,17,19 Tungsten disulfide (WS2) is a semiconducting TMDC, which has an indirect band gap of 1.3-1.4 eV in bulk in the common 2H and 3R phases, which have trigonal prismatic coordination around tungsten and only differ in the stacking of the WS2 layers.…”