First-principles study of tunable anisotropy in silicon superlattices for directionally selective channels

We use first-principles electronic-structure and lattice-dynamics calculations to identify dynamically stable configurations of silicon-compatible superlattices with Si/O or Si/Ge monolayers and Si/2Ge bilayers that provide a materials-level handle for engineering in-plane transport anisotropy in silicon channels. Across controlled periodicities, we quantify pronounced, tunable in-plane anisotropy in transport-relevant band curvature: in Si/O stacks, the electron effective mass reaches ≈0.26m* along [1̄10] while reaching 1.6 m* along [110], whereas Si/Ge preserves in-plane symmetry and Si/2Ge favors transport along the Y axis. Bandgaps are concurrently adjustable by interface chemistry and period, with tunability ranging from ∼50 meV (Si/Ge) to ∼430 meV (Si/2Ge), enabling threshold-voltage control alongside directional transport design. Acoustic deformation potentials increase with interface density (≈11 to 24 eV), indicating stronger electron–phonon coupling and a practical trade-off between anisotropy and mobility. Interface-specific vibrational features, including high-frequency oxygen modes (20–26 THz) and tunable phonon gaps in Ge-containing stacks, further differentiate thermal transport. Together, these results provide practical guidelines based on periodicity and interface chemistry for engineering leakage-suppressing, directionally selective silicon channel materials that are directly relevant to advanced nanosheet MOSFET technologies.