Quantum modeling of light absorption in graphene based photo-transistors

Graphene based optical devices are highly recommended and interested for integrated optical circuits. As a main component of an optical link, a photodetector based on graphene nano-ribbons is proposed and studied. A quantum transport model is presented for simulation of a graphene nano-ribbon (GNR) -based photo-transistor based on non-equilibrium Green’s function method. In the proposed model a self-energy matrix is introduced which takes the effect of optical absorption in GNR channel into account. The self-energy matrix is treated as a scattering matrix which leads to creation of carriers. The transition matrix element is calculated for optical absorption in graphene channel and is used to obtain the optical interaction self-energy. The resulting self-energy matrix is added to retarded Green’s function and is used in transport equations for calculation of current flow in the photo-transistor. By considering the effect of optical radiation, the dark and photocurrent of detector are calculated and results are used for calculation of responsivity.