Transition from sub-Poissonian to super-Poissonian shot noise in planar cold cathodes

Abstract

In recently investigated cold cathodes, the energy distribution of the injected electron beam into vacuum is 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 of the thermal energy typical of thermionic cathodes. For a sufficiently large voltage across the vacuum gap, the low frequency shot noise power spectrum of the anode current is found to agree with the Schottky classical result at low value of the cathode emission current. At the onset of current self-quenching due to space-charge effects, there is first a shot-noise reduction followed by a shot-noise enhancement in the anode current fluctuations for emission current densities far into the saturation regime. 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.