ACTIVATING METHOD FOR CESIUM ACTIVATED III-V COMPOUND PHOTOCATHODE USING RARE GAS BOMBARDMENT

摘要

A method of manufacturing an electronic discharge tube including a photo-cathode, the active constituent of which comprises a strongly p-conductive A III -B V -compound, where A III is B, Al, Ga or In, and B v is N, P, As or Sb, which is activated by an alkali or alkaline earth metal, includes the steps of heating the un-activated compound in the tube to a temperature not exceeding 300 C. for at least two hours and then, before activation, bombarding a free surface of the compound with rare gas ions having an energy not exceeding 100 eV. Preferably the energy of the rare gas ions is halved for the final part of the treatment. As shown, the photo-cathode 4 of the tube is a monocrystalline. GaAs plate with its surface oriented in the (110) direction and coated with an epitaxially deposited GaAs layer 5, 10 microns thick, which is doped with 3 x 1019 atoms of zinc/c.c. After degreasing all electrodes in the tube by heating in chlorothene at 60 C. for 2 min., the tube is exhausted and heated at 275 C. for 4 hours. Pure argon is then admitted at 5 x 10-4 Torr and a glow discharge ignited between electrodes 7 and 8, and with the cathode held 100 v. negative with respect to electrode 7 an ion current of 30ÁA/sq. cm. is drawn to the cathode surface for 30 min. The voltage is then reduced to 50 volts and ion current drawn for another 15 min. After pumping away the argon, the photo-cathode may be activated by successive additions of caesium, from source 9, and oxygen as described in Specification 1,200,899.