We designed and fabricated triode emitters with self-aligned cathodes in recessed geometry to reduce gate currents. Both the self-aligned carbon-nanoparticle and carbon-nanotube cathodes in recessed-cathode triode structure showed substantial gate-current reduction. However, tiny gate currents, a few percent of anode currents, persisted as long as there was gate overhang in triode emitters with recessed-cathode structure, and we were able to reduce gate currents to negligible level only after removing gate overhang. We elucidated the near-complete gate-current reduction of recessed-cathode triodes without gate overhang via two-dimensional electron-trajectory simulation based on numerical calculation of electrostatic potential using the commercial finite-element-method code ANSYS. (c) 2006 American Vacuum Society.