Amorphous semiconductors for cold cathodes: A route to large-area flat-panel displays

Abstract

The field-emission-display (FED) technology examined in the early sixties used metal tips or Spindt cathodes in order to extract electron beams to excite phosphors. The tips were necessitated by the large work function the electrons needed to overcome in order to be released into the vacuum. In the early nineties it was noticed that 'flat' diamond surfaces emitted electrons at relatively low electric fields. Just as its crystalline counterparts, amorphous-carbon thin films also showed that this class of materials were also capable of electron emission at low threshold fields. By using flat emitters, technologist can remove a number of fabrication steps that otherwise would have been required to produce large-area arrays of field emitters and therefore reduce the cost of production significantly. This paper will review the progress of the use of flat amorphous semiconductors as cold cathodes. New results that appear to point towards a space-charge-controlled emission mechanism as opposed to a purely surface emission process based upon Fowler-Nordheim tunneling will be introduced, which have implications on the type of device structure that will ultimately be needed for electron field-emission devices. Two possible cold-cathode materials, namely, amorphous-carbon and amorphous silicon, will be examined.