GB1134681A - Improvements in or relating to electric discharge devices - Google Patents

Abstract

1,134,681. Cathode materials and processing; cathode-ray tubes; projection devices. GENERAL ELECTRIC CO. Ltd. 22 Aug., 1966 [26 July, 1965], No. 31894/65. Headings H1D and H1K. In a cold-emitter cathode comprising a body of semi-conductor material having an N-type surface layer 2 overlying a P-type layer 3 to provide a PN junction 4, at least one recess 5 which extends to or through the PN junction is formed in the N-type surface layer 2, so that when a reverse bias voltage is applied across the junction electrons are liberated from the parts of the junction exposed within the recess. The semi-conductor material may be a single planar crystal of silicon carbide doped with aluminium for the P-type layer and with nitrogen for the N-type layer. The recess 5 which may be in the form of a frusto-conical hole or may be a labyrinth may be coated with a work function reducing material such as barium or caesium. The PN junction cathode may be employed in the electron gun of a cathode-ray tube and may have a number of recesses each associated with electrodes of a different gun assembly to produce a number of separate electron beams from the single cathode. The electron beam intensity may be controlled by the voltage across the PN junction. The cathode may also be used in demountable devices. The recess 5 may be formed using an ultrasonic drill and the inside surfaces of the hole polished with an abrasive by inserting a polishing slurry and a rotating metal rod into the hole. The crystal is then cleaned by boiling acid solutions. Further chemical treatment of the crystal to improve its emission properties may include immersion in specific acid solutions, boiling in acid and etching, and oxidation of the crystal surface and subsequent removal of the oxide.