Experimental evaluation of the extended Schottky model for ZrO/W electron emissionThe reduced brightness for a ͗100͘ ZrO/W Schottky electron emitter with a tip radius of 0.8 m has been measured. The maximum reduced brightness measured was 2ϫ10 8 A/͑m 2 sr V͒. The measurements of the reduced brightness are compared with the extended Schottky theory and the theory on stochastic Coulomb interactions. At high angular current densities the reduced brightness is limited by statistical Coulomb interactions in the gun lens region. The limits to the maximum reduced brightness in an ideal configuration are explored and found to be 2ϫ10 9 A/͑m 2 sr V͒ for a 0.2 m tip and a current limiting aperture in the extractor electrode.

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p-doped silicon field emitters were studied experimentally to assess their usefulness in multibeam electron lithography. Both individual emitters and emitter arrays were fabricated from single crystal Si wafers with several doping levels. Current-voltage curves were measured for different temperatures and illumination conditions. The typical plateaus in the I-V curves and the sensitivity to light known from the literature were reproduced. Stability measurements showed a very stable total emission current even while the angular emission distribution fluctuated strongly, giving unstable currents in apertured beams. Measured light response times varied between 34 ns and 20 µs, depending on experimental conditions. It was found that in the plateau of the I-V curve, the energy of the electrons shifts over up to 100 eV when changing the extraction voltage over a few kilovolts. In operation, when the current is stable, the energy shift is rather unstable. The experimental results are discussed within a model of the emission process involving an induced p-n junction inside the tip. The conclusion is that p-doped silicon field emitters are not particularly useful for applications in electron beam lithography.

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