Unlocking 2H-Ge: A Predictive k.p Model for Spin and Band Properties

Hexagonal germanium (2H-Ge), a direct band-gap group-IV semiconductor, holds promise for optoelectronics and optically addressable spin qubits, yet its electronic properties remain incompletely understood. We develop a 10-band k.p model, including spin-orbit coupling and fitted to ab-initio data, to analyze the band structure at the Γ-point. Our model accurately reproduces band curvatures, yielding previously unknown inverse effective mass parameters and precise values for electron and hole effective masses. To resolve the weak dipole coupling across the fundamental gap, we show that an expanded 12-band model is required. This reveals a spin-orbit-induced hybridization between the two lowest conduction bands, which explains the suppressed transition strength. Furthermore, we derive effective low-energy Hamiltonians for both conduction and valence bands for transport and spintronics applications via Löwdin's partitioning. Finally, we predict the electron and hole g-factors under an external magnetic field.