Conical Si field emitter arrays with gate electrodes have been fabricated. Emitter tips were doped by using an ion implantation technique so as to control the emission characteristics. The doped emitters with n-type surfaces showed typical held emission characteristics. However, the p-type emitters did not work well with the Fowler-Nordheim theory and showed plateaus in the Fowler-Nordheim plots. It is speculated from the capacitance-voltage measurements and the experiment of photoenhanced emission that the emission current is limited due to the supply of electrons from depletion layers near the emitter tips and from inversion layers under the gate electrodes.