Excitons in a Family of Anisotropic Two-Dimensional Orthorhombic ABC ₂ Monolayers (A = Mg and Ca; B = Ge and Sn; and C = S, Se, and Te)

Two-dimensional (2D) materials that combine high carrier mobility with substantial exciton binding energies ( E b ) are highly desirable for practical applications in electronics and optoelectronics. Here, we systematically investigate the optoelectronic and excitonic properties of orthorhombic PbSnS 2 -like monolayers, denoted as ABC 2 (A = Mg and Ca; B = Ge and Sn; and C = S, Se, and Te), using high-precision G 0 W 0 and Bethe–Salpeter equation calculations. Our results indicate that most of these ABC 2 monolayers host desirable direct band gaps and a fascinating visible light absorption range. Moreover, these ABC 2 monolayers host highly anisotropic carrier mobilities (up to 9.07×10 4 cm 2 V –1 s –1 ), originating from the asymmetric sublattices monolayer. Importantly, these ABC 2 monolayers have a robust linear scaling law between the E b and the quasiparticle band gap ( E QP ), namely, E b ≈ 1/3 E QP, which is significantly different from that of 2D hexagonal and tetragonal crystals. Our findings not only provide some promising ABC 2 optoelectronics materials but also enrich the understanding of the exciton properties of 2D materials.