Predicted behavior of a proposed novel hexa-structured layered Sb2S3: potential optoelectronic applications in the GHz range

Abstract

This study investigates a proposed novel layered orthorhombic phase of antimony sulfide (Sb₂S₃) using first-principles density functional theory (DFT). The theoretical analysis reveals strong anisotropy in the electronic and optical properties, with metallic character along the in-plane (x/y) directions and a small direct band gap (0.44–0.52 eV) along the out-of-plane (z) direction. A band gap value of 0.44 eV is obtained from band-structure calculations, while that of 0.52 eV is derived from Tauc plot analysis. Dielectric tensor analysis shows Drude-like behavior, with negative real permittivity in selective wavelength regions, indicating that the material functions as a natural hyperbolic metamaterial (HMM)—specifically, type-I in the 70–100 nm range and type-II in the 120–150 nm range. This property enables subwavelength wave propagation along specific crystal directions, suggesting potential applications in chip-integrated waveguides, UV-visible photonic circuits, and GHz-range optoelectronic devices. The high optical absorption, metallic conductivity, and Lorentz oscillator-fitted optical response—comparable to noble metals—position this phase of Sb₂S₃ as a promising candidate for anisotropic plasmonic devices, hyperlensing, and directional photodetection. These insights provide a pathway toward utilizing this natural HMM structure in future photonic, plasmonic, and photovoltaic technologies.