Anisotropic 2D Mo8S4Se8 and Mo8Se4S8 Semiconductors with Excellent Stability and High Carrier Mobility for Optoelectronics

Abstract

Two-dimensional (2D) semiconductors are regarded as highly advantageous materials for the progression of next-generation optoelectronic technologies. Nonetheless, their practical application is frequently constrained by intrinsically low carrier mobility under ambient conditions. In this work, we systematically investigate various crystalline phases of Mo8S4Se8 and Mo8Se4S8 (Mo8X4M8) monolayers using first-principles density functional theory (DFT) calculations, with an emphasis on their structural stability, elastic mechanical performance, electronic band structures, visible-light optical absorption, and anisotropic carrier mobility. Formation energy, cohesive energy, phonon dispersion spectrum, and room-temperature ab initio molecular dynamics (AIMD) simulations are combined to validate lattice stability under ideal vacuum conditions at 300 K, while deformation potential theory is applied to evaluate anisotropic carrier transport. Calculation results confirm that all of the considered phases exhibit intrinsic lattice stability within the simulated vacuum environment. Electronic structure analysis shows that the Cmmm, Amm2, and Cmm2-Mo8X4M8 monolayers behave as intrinsic semiconductors, with HSE06-calculated band gaps ranging from 1.32 to 1.49 eV. Moreover, these monolayers showcase ductility characteristics and optical absorption coefficients on the order of 105 cm–1 within the visible region. Remarkably, they exhibit substantial anisotropic carrier mobility, with hole mobility along the y-axis reaching up to 104 cm2 V–1 s–1. Overall, these Mo8X4M8 monolayers further expand the repertoire of Mo8-based 2D optoelectronic materials and represent promising candidates for future nanoelectronic and sensor applications.