Graphene-based bipolar spin diode and spin transistor: Rectification and amplification of spin-polarized current

Using nonequilibrium Green's function method combined with density functional theory we report bipolar spin diode behavior in zigzag graphene nanoribbons (ZGNRs). Nearly +/- 100% spin-polarized current can be generated and tuned by a source-drain voltage and/or magnetic configurations in these two-terminal bipolar spin diodes. This unique transport property is attributed to the intrinsic transmission selection rule of the wave function of spin subbands near the Fermi level in ZGNRs. Moreover, the bias voltage and magnetic configurations of the two-terminal ZGNR-based spin diodes provide a rich variety of ways to control the spin current, which can be used to design three-terminal spin transistors. These ZGNRs-based components make possible the manipulation of spin-polarized current such as rectification and amplification for carbon-based spintronics.