Electric field induced pure spin-photo current in zigzag stanene and germanene nanoribbons

The spin-photo current in single layer stanene and germanene under a linearly polarized light is theoretically investigated based on the tight-binding Hamiltonian combined with the nonequilibrium Green's function at room temperature. The results show that by considering the simultaneous effect of the linear illumination and a vertical external electric field without any magnetic exchange element, pure spin-photo current without charge current is generated in two-dimensional lattices with a large intrinsic spin-orbit coupling. The necessity of enhanced spin life-time for detection of spin polarization can be explained by spin-valley locking concept. Spin-valley locking arises in buckled two-dimensional materials as a result of the large spin-orbit coupling and electric-field reversible valley spin polarization. Equal absorption of the linearly illumination at both valleys with different spin polarization, leads to pure spin-photo current injection. In addition, an acceptable photoresponsivity has been reported in a broad range of photon energy. The numerical results indicate high quantum efficiency with a maximum of nearly 83% and 50% for stanene and germanene, respectively. This work may pave theoretical reference toward design of new spin-optoelectronic devices based on satanene and germanene junctions with high performance.