2D Ca3Sn2S7 Chalcogenide Perovskite: A Graphene-Like Semiconductor with Direct Bandgap 0.5 eV and Ultrahigh Carrier Mobility 6.7 x 104 cm2 V-1 s-1

Graphene, a star 2D material, has attracted much attention because of its unique properties including linear electronic dispersion, massless carriers, and ultrahigh carrier mobility (10(4)-10(5) cm(2) V-1 s(-1)). However, its zero bandgap greatly impedes its application in the semiconductor industry. Opening the zero bandgap has become an unresolved worldwide problem. Here, a novel and stable 2D Ruddlesden-Popper-type layered chalcogenide perovskite semiconductor Ca3Sn2S7 is found based on first-principles GW calculations, which exhibits excellent electronic, optical, and transport properties, as well as soft and isotropic mechanical characteristics. Surprisingly, it has a graphene-like linear electronic dispersion, small carrier effective mass (0.04 m(0)), ultrahigh room-temperature carrier mobility (6.7 x 10(4) cm(2) V-1 s(-1)), Fermi velocity (3 x 10(5) m s(-1)), and optical absorption coefficient (10(5) cm(-1)). Particularly, it has a direct quasi-particle bandgap of 0.5 eV, which realizes the dream of opening the graphene bandgap in a new way. These results guarantee its application in infrared optoelectronic and high-speed electronic devices.