▎ 摘　　要

The transmission of electrons in graphene-based p-n and n-p-n junctions on a SiC substrate is investigated. When we irradiate a beam of off-resonant light on a p-n junction, the transmitted angles of electrons from different valleys are unequal, which is similar to the birefringence of light. This is due to the valley polarization induced by the competition between the SiC substrate and the off-resonant light. In addition, a light-modulated fully valley polarized current is realized. In the case of n-p-n junction, we find light-modulated valley-dependent Brewster-like angles at which the electron from one valley is totally transmitted, while the electron from the other valley is totally reflected due to the valley polarization. Furthermore, we propose a new type of tunneling resistance in a graphene-based n-p-n junction irradiated by the off-resonant light. The tunneling resistances have different magnitudes for the different orientations of light and even can show giant magnetoresistance-like effect due to the valley polarization. This is different from the traditional giant magnetoresistance effect in the ferromagnet-insulator-ferromagnet junction, where the spin degree of freedom plays a key role. Published under license by AIP Publishing.