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 (Eb) are highly desirable for practical applications in electronics and optoelectronics. Here, we systematically investigate the optoelectronic and excitonic properties of orthorhombic PbSnS2-like monolayers, denoted as ABC2 (A = Mg and Ca; B = Ge and Sn; and C = S, Se, and Te), using high-precision G0W0 and Bethe–Salpeter equation calculations. Our results indicate that most of these ABC2 monolayers host desirable direct band gaps and a fascinating visible light absorption range. Moreover, these ABC2 monolayers host highly anisotropic carrier mobilities (up to 9.07×104 cm2 V–1 s–1), originating from the asymmetric sublattices monolayer. Importantly, these ABC2 monolayers have a robust linear scaling law between the Eb and the quasiparticle band gap (EQP), namely, Eb ≈ 1/3 EQP, which is significantly different from that of 2D hexagonal and tetragonal crystals. Our findings not only provide some promising ABC2 optoelectronics materials but also enrich the understanding of the exciton properties of 2D materials.