In thermionic cathodes, the onset of current self-quenching due to the space-charge built-up in the vacuum gap between cathode and anode leads to shot noise reduction in the anode current. This effect has been observed experimentally and has been analyzed by several authors using analytical and computational techniques. In recently proposed cold cathode structures, the energy distribution of the injected electron beam into vacuum can be quite different from the hemi-Maxwellian distribution typical of thermionic cathodes. We use an Ensemble Monte-Carlo technique to study shot noise in planar cold cathodes in which the emission into vacuum is characterized by an average injection energy far in excess to the thermal energy typical of thermionic cathodes. For a specific cold cathode structure, biasing conditions and cathode parameters are found for which the low frequency shot noise power spectrum of the anode current exceeds the Schottky classical result. It is shown that this shot noise enhancement is due to large fluctuations in both energy and space of the maximum of the energy potential hump in front of the cathode.
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