A highly integrated solid-state plasma metasurface based on a GaAs/AlGaAs superlattice structure

Conventional solid-state plasma metasurfaces are limited by silicon-based structures, suffering from low carrier concentration, non-uniform distribution, and high electromagnetic loss and poor integration density caused by an excessively thick intrinsic region. To address these issues, this paper proposes and designs a highly integrated solid-state plasma metasurface based on a GaAs/AlGaAs superlattice structure. First, the electrical characteristics of solid-state plasma units based on conventional silicon-based structure, GaAs/AlGaAs heterojunction, and GaAs/AlGaAs superlattice structures are comparatively analyzed. Theoretical analysis and simulation results show that, owing to the quantum confinement effect and resonant tunneling characteristics of its periodic potential wells, the solid-state plasma concentration based on the GaAs/AlGaAs superlattice structure reaches 4×10¹⁹ cm^-3, with an intrinsic region thickness of only 5 μm. Meanwhile, the uniformity of carrier concentration distribution along the horizontal direction is significantly better than that of heterojunction and homojunction structures. Based on this superlattice unit, a 1-bit coding metasurface with geometrically fixed phase distribution and electrically switchable amplitude modulation is further designed. The dimensional parameter K of the top metal electromagnetic modulation structure, set to 89 μm and 100 μm, corresponds to reflection phases of -80.9^o and 100.1^o, respectively, with a reflection amplitude greater than 0.94 at 1.25 THz and an amplitude modulation depth of 84.1%. The units are arrayed to form 16×16 super-subunits (each super-subunit contains 3×3 basic units). Simulation results show that the designed 1-bit coding metasurface, with its fixed phase encoding, achieves beam steering, while its reflection amplitude can be dynamically modulated by the applied bias, thereby verifying the effectiveness of the design.