Performance of laser ablated, laser annealed BN emitters deposited on polycrystalline diamond

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Thin BN films of about 100 nm were deposited on 25 μm thick n-type polycrystalline diamond by laser ablation and annealed with a 25 ns pulse from an excimer laser at 0.1 J. Current densities of about 2 A/cm2 were obtained with an extraction electrode probe area of 2×10−3 cm2 (500 μm diameter). Emission is governed by a Fowler–Nordheim-type behavior with some deviation at higher currents due to the voltage dependency of the BN resistance. From present experiments it cannot be deduced if the films exhibit negative electron affinity. Emission currents are stable and independent of pressure to about 10−4 Torr. The magnitude of the current fluctuations are similar to Spindt-type devices. Compared to Mo and Si emitters, no careful high vacuum conditioning procedure is needed prior to operation. At current densities above 1 A/cm2, restructuring of the emission area took place at some locations of the 0.5 cm × 1 cm sample, leaving craters in the diamond substrate. After restructuring, emission still took place with modified current–voltage characteristics. Based on these results, carbon-doped BN has the potential for creating very rugged, low noise, high current density cold electron sources.