SEM pictures showing the structure of a high packing density emitter array with 2 (a) and scales (b). The FEA has a active area of emitters with pitch and gate aperture opening.
Cross-section illustration of the major steps in the fabrication process. (a) Semi-isotropic RIE to form Si cones, (b) thermal oxidation to form sharp Si tips, (c) e-beam deposition of Cr, and (d) three-step etch (metal cap etch/oxide dry etch/oxide wet etch) to remove oxide around only the apexes of the tips.
Plot of current vs inverse gate voltage of the dark current for the high packing density FEA at room temperature (and a modified FN plot on the inset) showing a distinct transition at gate voltage of 50 V between the metal-like FN low voltage regime I and the saturated high voltage regime II. The red arrow indicates the range of photoassisted field emission for applied gate voltage of 100 V.
Schematic experiment arrangement for measurement of photoexcited emission current from FEA with 110 fs optical pulses at . The FEA vertical arrangement of gate metal, oxide layer, and -type Si substrate is shown, and the inversion and depletion layer thickness are indicated. The depletion layer depth is and the optical absorption depth is .
Oscilloscope traces for the response of FEA to light well focused on the high density FEA at gate voltage of 120 V. The vertical scale is 1 mV/division. The horizontal time scales are 100 ns, 20 ns, 1 ns, and 100 ps per division for the traces from (a) to (d), respectively.
Oscilloscope traces for the optical pulse response of FEA at gate voltage of 110 V for the low density FEA device. The bottom trace was obtained with a delay scan function from the window in the top trace. The vertical scale is per division and the horizontal time scales for the top and bottom trances are and 100 ns per division, respectively. In this measurement the optical spot diameter was , and substantial excitation occurred outside the gated region.
Oscilloscope traces for the optical pulse response of FEA with various gate voltages ranging from saturated (a) 50, (b) 70, (c) 90, and (d) 110 V for the high density FEA device. The vertical and horizontal time scales are 1 mV/division and 100 ns/division, respectively.
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