Tunable absorbance and polarization modulation in phosphorene–hexagonal boron nitride heterostructures in the terahertz regime

Two-dimensional materials offer unique opportunities for manipulating light-matter interactions at the nanoscale. Phosphorene, a single layer of black phosphorus, possesses a tunable band gap and strong in-plane anisotropy, leading to pronounced linear dichroism. Hexagonal boron nitride (hBN) is a wide band gap van der Waals dielectric with inherent anisotropy and a hyperbolic dispersion in the mid infrared. While both materials have been studied extensively in isolation, how their combined optical responses evolve in a phosphorene/hBN heterostructure is not yet fully understood. Here we demonstrate that phosphorene/hBN heterostructures exhibit markedly different reflection and absorption spectra compared to their individual components. In particular, we identify a robust, polarization insensitive absorption peak near the in-plane transverse optical phonon frequency of hBN. Conversely, the absorbance near the in-plane and out-of-plane longitudinal optical phonon frequencies can be tuned by varying the phosphorene surface conductivity, giving rise to polarization sensitive resonances. We further show that, for transverse electric (TE) and transverse magnetic (TM) polarized light, the absorbance evolves in opposite directions as the incidence angle changes. Our findings clarify the underlying optical interactions in phosphorene-hBN layered structures and significantly enhance the potential for designing advanced polarization-based optoelectronic devices.