EMISSION CHARACTERISTICS AND MORPHOLOGY OF WET ETCHED CATHODES IN P-TYPE SILICON

An isotropic wet etching process was used to generate arrays of field emitting, square-based pyramidal cathodes on (001), p-type silicon wafers. Their general morphology compared well with that found by Cade et al.,1 except that for cathodes with edges oriented along [110] directions, a ridgelike apex was formed. Transmission electron microscope examination of oxidized tips confirmed that tip sharpening occurs, improving the aspect ratio and producing two sharp cusps from a ridgelike apex and a single sharpened tip from a pointed apex. A modified Philips 505 SEM was used to make electrical measurements from the arrays. Measurements could be made over the range 1-2500 V with a current sensitivity of 10(-13) A, current readings being taken over 6 orders of magnitude, in a vacuum of 3 X 10(-7) Torr. Fowler-Nordheim plots exhibited characteristics typical of p-type silicon showing a plateau region which was eliminated by coating with metal. Oxidation sharpening was shown to improve emission and the lowest voltage at which electron emission occurred from a given tip was found to decrease with emission time.