AOBiX2 (A = La, Tb, Lu; X = S, Se): a family of 2D narrow bandgap semiconductors with high stability, broad-spectrum response, flexibility and high carrier mobility

Abstract

In recent years, two-dimensional (2D) materials have attracted significant attention in the field of photodetection due to their unique physical and chemical properties. However, the development of new 2D semiconductors with narrow bandgaps, high carrier mobility, and excellent optical absorption remains a substantial challenge. In this study, via first-principles calculations, a family of 2D semiconductors, AOBiX₂ (A = La, Tb, Lu; X = S, Se), is predicted to exhibit the desired properties. Specifically, the thermodynamic, dynamic, thermal, and mechanical stabilities of AOBiX₂ are assessed by analyzing their formation energies, phonon dispersion, ab initio molecular dynamics (AIMD) simulations, and elastic constants, respectively. Furthermore, the adsorption energy calculations demonstrate that AOBiX₂ retains stability in a humid/oxygen environment. Electronic structure analysis reveals that 2D AOBiX₂ has ideal narrow bandgaps (ranging from 0.52 to 0.80 eV) and high carrier mobility (up to 5137.94 cm²/(V·s) for LaOBiS₂). The photoconductivity is also calculated to explain the optoelectronic response characteristics of these materials, further confirming their exceptional performance in optoelectronic devices. Optical properties show that these materials have an extremely broad absorption range, covering the near-infrared (NIR) to visible and ultraviolet (UV) regions, with the optical absorption rate exceeding 26%, indicating excellent optical absorption performance. Additionally, their elastic properties exhibit remarkable flexibility, making them ideal candidates for the design and fabrication of flexible optoelectronic devices. Given that the cleavage energies of AOBiX₂ are even lower than those of graphene, these materials are promising candidates for experimental fabrication and provide ideal platforms for designing new high-performance photodetectors.