A photoconductive terahertz emitter based on nanoscale contact electrode gratings is presented and experimentally demonstrated. The nanoscale grating enables ultrafast and high quantum efficiency device operation simultaneously, by reducing the photo-generated carrier transport path to photoconductor contact electrodes. The presented photoconductor eliminates the need for a short-carrier lifetime semiconductor, which limits the efficiency of conventional photoconductive terahertz emitters. A photoconductive terahertz emitter based on the presented scheme is implemented and integrated with 0.5 THz dipole antenna arrays. Emitted radiation is characterized in a terahertz time-domain spectroscopy setup, measuring a full width at half maximum response time of 670 fs.