Towards high-performance p-type two-dimensional field effect transistors: contact engineering, scaling, and doping

Abstract

N-type field effect transistors (FETs) based on two-dimensional (2D) transition metal dichalcogenides (TMDs) like MoS2 and WS2 have come closer to meeting the requirements set forth in International Roadmap for Devices and Systems (IRDS). However, p-type 2D FETs are dramatically lagging behind in meeting performance standards. Here, we adopt a three-pronged approach that includes contact engineering, channel length (Lch) scaling, and monolayer doping to achieve high-performance p-type FETs based on synthetic WSe2. Using electrical measurements backed by atomistic imaging and rigorous analysis, Pd was identified as the favorable contact metal for Wse2 owing to better epitaxy, larger grain size, and higher compressive strain leading to lower Schottky barrier height. While the ON-state performance of Pd-contacted WSe2 FETs was improved by ~10× by aggressively scaling Lch from 1 µm down to ~ 20 nm, ultra-scaled FETs were found to be contact limited. To reduce the contact resistance, monolayer tungsten oxyselenide (WOxSey) obtained using self-limiting oxidation of bilayer WSe2 was used as p-type dopant. This led to ~ 5× improvement in the ON-state performance and ~ 9× reduction in the contact resistance. We were able to achieve a median ON-state current as high as ~ 10 µA/µm for ultra-scaled and doped p-type WSe2 FETs with Pd contacts. We also show the applicability of our monolayer doping strategy to other 2D materials, like MoS2, MoTe2, and MoSe2.

Room Temperature Negative Differential Resistance with High Peak Current in MoS2/WSe2 Heterostructures

“…In contrast, Cr/Au contacts on few-layer WSe 2 exhibit n-type transport while the vdW Pt contacts show p-type-dominant behavior. 19 This result is consistent with previous studies showing that vdW contacts are effective in achieving p-type transport in WSe 2 . 15,20 In addition, temperature-dependent transport measurements showing stable transport behavior over a large temperature range are shown in Figure S2.…”

Simulations of Anisotropic Monolayer GaSCl for p-Type Sub-10 nm High-Performance and Low-Power FETs

“…However, most of the FETs mentioned above are n-type. Despite the development of p-type FETs, 17−20 current research on p-type FETs lags far behind that of n-type, 21 which greatly limits the development of complementary logical circuit transistors. 22,23 The monolayer FeOCl-type materials have attracted great attention because of their unique anisotropic structures.…”

Lateral homojunctions of WSe2 through contact surface engineering with SF6 plasma etching

“…22,23 Yoo and co-workers 24,25 recently reported that the p-doping of exfoliated WSe 2 was significantly enhanced by O 2 plasma treatment, an aging effect can be utilized to address the Fermi-level pinning (FLP) issue specifically related to metal/2Dsemiconductor contact, and electron beam irradiation can be employed to fine-tune the doping concentration induced by O 2 plasma treatment. Oberoi et al 26 achieved high-performance ptype conduction in a monolayer WSe 2 with O 2 plasma treatment of the CVD-synthesized bilayer in combination with contact engineering and channel length scaling.…”