Strongly anisotropic optoelectronic properties and long exciton lifetimes in two-dimensional GaInS₃-type monolayers

Two-dimensional (2D) layered GalnS₃ materials have attracted huge attention due to their excellent anisotropic photoelectric properties for photovoltaic devices. However, the monolayer α-GaInS₃ possesses an indirect band gap, which significantly limits its practical applications. Therefore, we constructed non-centrosymmetric GalnS₃-like monolayers, namely, ABM₃ (A = Ga, In, Al; B = Ga, In, Al; M = S, Se, Te), and investigated their electronic and excitonic properties using high-precision G₀W₀-BSE methods. Our results indicated that β-GaInS₃, GaAlSe₃, and AlInSe₃ monolayers possess direct band gaps with desirable structural stability. Moreover, the built-in electric potential differences of these non-centrosymmetric monolayers can promote the separation of photon-generated carriers. Importantly, the three ABM₃ monolayers exhibit larger exciton binding energy with a BSE optical band gap in the visible light range, and their exciton lifetime is up to 7.05 ps for β-GaInS₃ at 0 K. In addition, these three structures exhibit highly anisotropic electron mobilities (up to ∼10³ cm² V^-1 s^-1) due to their larger lattice anisotropy.