Li Intercalation Effects on Interface Resistances of High‐Speed and Low‐Power WSe₂ Field‐Effect Transistors

Abstract

Van der Waals (vdW) layered materials are promising channel materials for next-generation field-effect transistors (FETs). However, in vdW layered-material FETs, the Schottky barrier and tunnel barrier at the vdW interfaces significantly reduce the electron injection efficiencies at electrical contacts, thereby limiting the development of high-speed and low-power FETs. This study demonstrates that intercalated lithium (Li) ions at vdW interfaces lower the Schottky and tunnel barriers at the electrical contacts of multilayer tungsten diselenide FETs owing to the low potential energy of Li and the mild electron doping from intercalation, thus decreasing the resistance at the vdW interfaces and enhancing the current flow and field-effect mobility. Compared with before-Li intercalation, the multilayer WSe 2 planar FET demonstrates ≈1000 times higher current (I DS = 17.8 µA) at V GS = 50 V, ≈110 times higher maximum field-effect mobility (µ FE = 97.67 cm 2 V −1 s −1), and ≈1000 times higher on/off current ratio (on/off ratio = ≈10 7). Furthermore, in multilayer WSe 2 vertical FETs with vdW heterostructures having a structural strength of approximately the same as the current density, the intercalated Li ions at the graphene/WSe 2 vdW interfaces additionally improves the current density and the vertical mobility by ≈20 times (1.00 A cm −2) and 10 times (2.52 × 10 −4 cm 2 V −1 s −1), respectively. This study establishes a method to reduce the resistance at vdW interfaces for developing high-speed and low-power multilayer vdW material FETs.

Tuning electrical and interfacial thermal properties of bilayer MoS2 via electrochemical intercalation

“…When the MoS 2 flake was fully lithiated to Li 1.0 MoS 2 (red curve), the channel became metallic as MoS 2 underwent a 2H (semiconducting) to 1T (metallic) phase transformation upon lithiation as previously reported [16,18,35,36]. We observed ∼500×improvement in drive current I on upon Li intercalation (Li 1.0 MoS 2 ) likely because of the higher carrier concentration [29] (∼200×) upon intercalation as well as lower contact resistance due to the semiconducting-to-metallic phase transition [18,45]. This 2H to 1T phase transition is likely triggered by the strain from the influx of Li ions [46].…”

Selective Electron Beam Patterning of Oxygen‐Doped WSe2 for Seamless Lateral Junction Transistors

“…However, ion implantation used in conventional Si technology is not compatible with 2D TMDs owing to the fragile thin body against highenergy ion bombardment. Various doping methods have been proposed for 2D materials, such as substitutional doping, [5,6] intercalation doping [7][8][9] and electrostatic doping. [10,11] Nevertheless, such strategies have had limited success in terms of longterm stability, low device-to-device variability, and low-temperature processing.…”

Paraffin-Enabled Compressive Folding of Two-Dimensional Materials with Controllable Broadening of the Electronic Band Gap

“…Semiconductive TMDs mostly possess electronic band gaps below 1.80 eV . A wider band gap is particularly useful in optoelectronic devices such as light-emitting diodes, − field effect transistors (FETs), − and photodetectors , because they are crucial in suppressing tunneling from source to drain electrodes, leading to larger on/off ratio and higher mobility. Moreover, semiconductor with wider band gap absorbs blue and ultraviolet light with high energy.…”