  We observe a dc electric current in response to terahertz radiation in
lateral inter-digitated double-comb graphene p-n junctions. The junctions were
fabricated by selective ultraviolet irradiation inducing p-type doping in
intrinsic n-type epitaxial monolayer graphene. The photocurrent exhibits a
strong polarization dependence and is explained by electric rectification in
p-n junctions.
