Janus structures of the C2h polymorph of gallium monochalcogenides: first-principles examination of Ga2XY (X/Y = S, Se, Te) monolayers

Abstract

Group III monochalcogenide compounds can exist in different polymorphs, including the conventional D_3h and C_2h phases. Since the bulk form of the C_2h-group III monochalcogenides has been successfully synthesized [Phys. Rev. B: Condens. Matter Mater. Phys. 73 (2006) 235202], prospects for research on their corresponding monolayers have also been opened. In this study, we design and systematically consider a series of Janus structures formed from the two-dimensional C_2h phase of gallium monochalcogenide Ga₂XY (X/Y = S, Se, Te) using first-principles simulations. It is demonstrated that the Janus Ga₂XY monolayers are structurally stable and energetically favorable. Ga₂XY monolayers exhibit high anisotropic mechanical features due to their anisotropic lattice structure. All Janus Ga₂XY are indirect semiconductors with energy gap values in the range from 1.93 to 2.67 eV. Due to the asymmetrical structure, we can observe distinct vacuum level differences between the two surfaces of the examined Janus structures. Ga₂XY monolayers have high electron mobility and their carrier mobilities are also highly directionally anisotropic. It is worth noting that the Ga₂SSe monolayer possesses superior electron mobility, up to 3.22 × 10³ cm² V⁻¹ s⁻¹, making it an excellent candidate for potential applications in nanoelectronics and nanooptoelectronics.