Terahertz source with graphene p-n junction

The gate-controlled graphene with two top gates shows that the positive gate voltage can move the Fermi level to higher energy towards conduction band, whereas the negative gate voltage will move the Fermi level to lower energy towards valence band to form graphene p-n junction. The band gap between the n-type graphene and the p-type graphene can be tuned from 0eV. When the induced n-type Fermi level is bigger than 2.15meV, it is possible to radiate terahertz photon if the electrons in n-type graphene are injected to p-type graphene to recombine with holes under a forward bias.