▎ 摘　　要

Graphene was predicted to have a long spin relaxation time in the range of microseconds to milliseconds due to its weak spin-orbit coupling and hyperfine interaction. However, very short spin relaxation times were measured experimentally on the order of nanoseconds. Magnetic proximity effect from spin valves were considered strongly to influence the electronic and spin properties in graphene. Here, a graphene/nonmagnetic semi-conductor CdX heterostructure is proposed to eliminate the magnetic effect and to fulfill optical injection of spin polarization. Based on the first-principles calculation within the density functional theory, we perform a sys-tematic study on the structural, electronic properties and band structures of the heterostructures, and find that graphene on CdX (X = S, Se and Te) slabs preserves its linear Dirac band structure within the bandgap of CdX, and a built-in electric field occurs near the interface. The built-in electric field drives spin polarized electrons into graphene preferably. An optical detection scheme of spin relaxation time of graphene is proposed based on Faraday and Hanle effects.