Design and Theoretical Analysis of a Dynamically Tunable Terahertz Broadband Absorber Based on a Graphene/MoS2 Vertical Heterojunction and VO2 Phase Transition

This paper proposes a tunable terahertz broadband absorber based on a graphene/MoS2 vertical heterojunction and a VO2 phase-change film. VO2 reconfigures the longitudinal Fabry–Perot cavity via its insulator-metal transition, switching between broadband absorption and weak reflection. graphene adjusts its Drude conductivity and kinetic inductance through its Fermi level, compensating for band-edge impedance mismatch and broadening the absorption band. MoS2 enhances local field confinement and Ohmic dissipation via intraband free-carrier response and interface charge transfer. The three materials form a synergistic mechanism of phase-change coarse tuning, electrical fine-tuning, and loss enhancement. Results show that in the VO2 insulating state, absorption exceeds 91.7% from 3.5 to 6.5 THz, with a relative bandwidth of 60.8%. Coupled mode theory decomposes the broadband absorption into three under-coupled modes, corresponding to low-frequency anchoring, mid-frequency bridging, and high-frequency enhancement. Unit peeling analysis shows that the eight asymmetric units achieve nonlinear synergy through near-field coupling and current topology reconstruction, rather than simple superposition. The device also exhibits less than 2% degradation under ±20% processing deviation. It maintains over 91.7% absorption within 0–60° incidence under TE polarization, demonstrating good process robustness and angle stability.