We experimentally present the effects of vertical alignment and density of carbon nanotubes on the emission current level. For practical display application, we have fabricated the triode type emitter using directly grown nanotubes as emission tip, and characterized their basic field emission properties. The triode type emitter exhibited a turn-on voltage of 37 V and an anode current density of 1.7 muA with gate voltage at 47 V The vertical alignment of nanotubes does not play a key role in improving the emission properties in triode type nanotubes emitter. (C) 2003 Elsevier Science B.V. All rights reserved.