▎ 摘　　要

Ballistic thermoelectric properties in graphene-nanoribbon-based heterojunctions are investigated by using the nonequilibrium Green's function approach and the Landauer transport theory. The results show that the phonon thermal conductances have similar effects for the different heterojunctions, while the electron transport is highly sensitive to the geometry details of the heterojunctions. The fluctuation of electronic transmissions can strongly enhance the thermopower. We can obtain the high thermoelectric figure of merit ZT similar to 0.6 at room temperature T = 300K and ZT similar to 0.9 at low temperature T = 100K by optimizing the thermopower, together with suppression of phonon transport by mismatching interface structures. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4751287]