Valley-Landscape Engineering in Bilayer WSe₂ Gate-All-Around Transistors

2026/06/30 by Katsunori Wakabayashi, Souren Adhikary, Kazuhito Tsukagoshi
Physics and Astronomy · #cond-mat.mes-hall #cond-mat.mtrl-sci

paper · pdf

18 pages, 7 figures

arxiv created 2026/08/05 · arxiv updated 2026/08/06

Abstract

The K-Γ valence-band splitting Δ_KΓ that governs hole transport in few-layer WSe₂ is not a fixed material constant. It is tuned by interlayer stacking, strain, pressure, and the dielectric and displacement-field environment. Its computed value also depends on the level of electronic-structure theory. Bilayer WSe₂ therefore realizes a tunable multivalley landscape rather than a single operating point. We combine first-principles inputs with an analytical two-valley device model for gate-all-around (GAA) field-effect transistors, and obtain three results. (i) The minimum subthreshold swing stays near the thermionic limit of 60~mV~dec^-1 independently of layer number, because well below threshold the quantum capacitance remains far below the oxide capacitance. (ii) The effective mobility is set by the K-to-Γ occupation ratio: valley redistribution is strong when Δ_KΓ is of order k_BT and fades toward single-valley K transport as the splitting grows. (iii) In this small-splitting regime, biaxial strain tunes the effective mobility - and hence the on-current - through the valley population while the subthreshold swing stays at the thermionic limit, decoupling mobility control from electrostatic switching in a way distinct from scattering-based strategies. A symmetric GAA gate controls carrier density at essentially fixed splitting, and because an out-of-plane field increases Δ_KΓ, its midplane-symmetric potential avoids driving the channel out of the small-splitting regime. The design principle has two facets: small Δ_KΓ - set by layer number, stacking, strain, and dielectric engineering - maximizes the valley tunability of μ_eff, whereas larger Δ_KΓ, for example through compressive strain, suppresses the heavy Γ valley and maximizes the on-state mobility.

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