Emission characteristics and morphology of wet etched cathodes in p-type silicon

Abstract

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 3×10−7 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.