Atomically Controlled Tunable Doping in High‐Performance WSe₂ Devices

Abstract

Two-dimensional transitional metal dichalcogenide (TMD) field-effect transistors (FETs) are promising candidates for future electronic applications, owing to their excellent transport properties and potential for ultimate device scaling. However, it is widely acknowledged that substantial contact resistance associated with the contact-TMD interface has impeded device performance to a large extent. It has been discovered that O2 plasma treatment can convert WSe2 into WO3-x and substantially improve contact resistances of p-type WSe2 devices by strong doping induced thinner depletion width. In this paper, we carefully study the temperature dependence of this conversion, demonstrating an oxidation process with a precise monolayer control at room temperature and multilayer conversion at elevated temperatures. Furthermore, the lateral oxidation of WSe2 under the contact revealed by HR-STEM leads to potential unpinning of the metal Fermi level and Schottky barrier lowering, resulting in lower contact resistances. The p-doping effect is attributed to the high electron affinity of the formed WO3-x layer on top of the remaining WSe2 channel, and the doping level is found to be 2 dependent on the WO3-x thickness that is controlled by the temperature. Comprehensive materials and electrical characterizations are presented, with a low contact resistance of ~528  m and record high on-state current of 320 A/m at -1V bias being reported.

Thickness-Dependent Study of High- Performance WS2-FETs With Ultrascaled Channel Lengths

“…This implies in particular that monolayer TMD devices are expected to receive strong contact gating and good injection into the channel, but the device ON-state may suffer from too large R C -values associated with a large SBH at the contact interface as mentioned above [18], [19]. Therefore, further studies on the topics of reliable doping schemes [25]- [29], phase change contacts [30], [31], and contact Fermi-level depinning [32]- [34] are urgently required to facilitate the integration of 2-D TMD-based CMOS for a beyond-Si era.…”

Control of the Schottky Barrier and Contact Resistance at Metal–WSe2 Interfaces by Polymeric Doping

“…Recently, Pang et al reported that surface dopants diffuse to the transfer length of devices even with the hard mask used for the electrical contact region. [41] Besides, they also reported the Fermi-level depinning by p-type doping. [42] Moreover, PVA as a dielectric layer provides a screening effect to long-range charge scattering, alleviating FLP.…”

Improving stability in two-dimensional transistors with amorphous gate oxides by Fermi-level tuning

“…At the same time, the intentional placement of charges at the interface could be used to shift the band edges away from the oxide defect bands using, for example, surface charge transfer doping 43 . However, fixed charges at the interfaces would also degrade the mobility in the semiconducting 2D channel 25 .…”