GB853352A - Improvements relating to electron emitters - Google Patents

Abstract

853,352. Discharge tubes ; cathode materials. METROPOLITAN-VICKERS ELECTRICAL CO. Ltd. Dec. 9, 1958 [Dec. 16, 1957], No. 39061/57. Class 39(1). A discharge tube includes a cathode comprising a body of homogeneous semi-conductor material and terminals or contacts at points spaced apart on the surface of said semiconductor body so that a voltage may be applied across it. The emission is stated to be due to a " hot electron " effect. Fields are required which, if applied for any length of time, would cause excessive heating of the semi-conductor lattice and disruption thereof. It is thus necessary to use a pulsed field of a maximum value less than the dielectric breakdown field of the particular material used. Some moderate heating of the lattice is advantageous as this leads to increased electron densities. It is also necessary to use semi-conductors with a sufficiently large forbidden energy gap to allow for high electron energies before avalanche breakdown sets in. Suggested suitable semi-conductors are the elements and compounds of the elements of Group IV of the periodic table, such as Ge, Si and SiC, which exhibit mobilities. The semi-conducting cathode may be coated with a substance of low work function, e.g. caesium. In one arrangement, Fig. 1, a disc 6 of semi-conductor material is mounted on an insulating block 7 carried on a base plate 1 of conducting material, e.g. copper, sealed by means of an insulating cylinder 3 to a plate 2 supporting a rod 4 carrying an anode disc 5. Conductor strips 8 and 9 extend from opposite edges of the disc 6 to a copper ring electrode 10 and the base plate 1 which are connected across a pulse generator 12. A high D.C. voltage is applied between the anode 5 and cathode 6 by a source 13. In an alternative embodiment, Fig. 2 (not shown), a rod of semi-conductor material is mounted axially in a conducting cylinder to form a diode. In a further alternative embodiment, Fig. 3, the semi-conductor material is in the form of a hollow cylinder 21 across which pulses are applied by a generator 12 connected to conducting rings 22 and 23. The anode 5 is supported by a rod 4 carried by an insulating plate 24. A disc 29, preferably of insulating material, is sealed across the ring 22. Additional accelerating electrodes similar to the ring 23 may be provided, Fig. 6 (not shown).