Janus structures of the C 2h polymorph of gallium monochalcogenides: first-principles examination of Ga 2 XY (X/Y = S, Se, Te) monolayers.

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 Ga 2 XY (X/Y = S, Se, Te) using first-principles simulations. It is demonstrated that the Janus Ga 2 XY monolayers are structurally stable and energetically favorable. Ga 2 XY monolayers exhibit high anisotropic mechanical features due to their anisotropic lattice structure. All Janus Ga 2 XY 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. Ga 2 XY monolayers have high electron mobility and their carrier mobilities are also highly directionally anisotropic. It is worth noting that the Ga 2 SSe monolayer possesses superior electron mobility, up to 3.22 × 10 3 cm 2 V -1 s -1 , making it an excellent candidate for potential applications in nanoelectronics and nanooptoelectronics.