A silicon negative affinity cold cathode

This talk describes research leading to the successful operation of silicon cold cathodes. This device is essentially a forward-biased silicon p-n junction whose p-surface is activated to a state of negative affinity. Electrons injected into the p-region diffuse to the surface where they are emitted into the vaucum. Contacting the p-layer without obstructing the emitted electrons can be a problem since this layer must be thin to permit efficient transport of the injected electrons to the surface, with the result that the junction may be biased only under and very near the contact. A Si:SiO2structure has been developed to overcome this problem, and, with this new structure, efficiencies (ratio of emitted current to bias current) as high as 10% have been observed with emitted current densities of over 200 A/cm². The plate characteristics clearly indicate emission-limited and space-charge-limited regions as well as Schottky effect. Although most of the data were taken pulsed, measurements of DC emission for many hours were also made. Calculations of the current density profiles across the Si:SiO2structures indicate that practical levels of operation can be achieved with reasonably uniform emission profiles. Sealed-off tubes have also been prepared, and preliminary data indicate that the cathodes are stable.