Bilayer TMDs for Future FETs: Carrier Dynamics and Device Implications

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Bilayer transition metal dichalcogenides (TMDs) are promising for advanced field-effect transistors (FETs) due to their unique electronic properties and atomic thinness.
• Understanding carrier transport in these materials is crucial for optimizing device performance.

Purpose of the Study:

• To compute electronic band structures and phonon dispersions of WS2, WSe2, and MoS2 using DFT.
• To investigate carrier transport, including electron-phonon scattering, dielectric screening, and interface excitation scattering.
• To simulate device-level performance of double-gate FETs using bilayer TMDs.

Main Methods:

• Density Functional Theory (DFT) for electronic and phonon properties.
• Electron-phonon Wannier (EPW) method for scattering rates.
• Semiclassical full-band Monte Carlo simulations for carrier transport.
• Device-level simulations of double-gate FETs.

Main Results:

• Freestanding WS2 and WSe2 bilayers show high hole mobilities (2300 and 1300 cm2/V·s, respectively).
• Hexagonal boron nitride (hBN) dielectric preserves/enhances mobility, while HfO2 significantly reduces it due to interface effects.
• Series resistance limits device performance; optimized WSe2 pFETs achieve 820 A/m ON current, enhanced by hBN.

Conclusions:

• First-principles calculations reveal the critical role of electronic structure and scattering physics in bilayer TMD transport.
• Material properties and dielectric environment strongly influence FET performance.
• Optimizing dielectric choice and mitigating series resistance are key for high-performance bilayer TMD FETs.