Inter-valley phonon scattering limited performance of n-channel WS 2 monolayer transistors

In addition to the K conduction band valley of monolayer WS 2 , there is a remote Q valley located 0.1 eV above the K valley. We investigate the effects of intra- and inter-valley phonon scattering, including K ↔ Q inter-valley scattering, on monolayer WS 2 device performance using a recursive Green’s function algorithm and the Büttiker probe scattering model. Our analysis reveals that ballisticity drops to 54% when only intra-valley phonon scattering is considered. When inter-valley phonon scattering (excluding K ↔ Q inter-valley scattering) is added, ballisticity decreases to 42%. This further declines to 12% with the inclusion of K ↔ Q inter-valley scatterings. Similarly, low-field mobility values decrease successively from 395 cm 2 ( V ⋅ s ) − 1 to 223 cm 2 ( V ⋅ s ) − 1 and then to 110 cm 2 ( V ⋅ s ) − 1 at a sheet density of 10 9 cm −2 . The primary scattering mechanism responsible for this degradation is K → Q inter-valley acoustic phonon scattering, characterized by a high deformation potential of 7.3 × 10 8 eV cm − 1 and a low energy of 16.76 meV. Additionally, K → Q inter-valley scattering significantly populates the Q valley, which presents a higher potential barrier in the on-state conduction band profile, resulting in a lower on-state current. Our analysis shows that approximately 40% of the on-state total power dissipated within the device is due to phonon scattering effects, with the remainder being released through thermalization in the device’s contacts.