Photoresponse of gated p-silicon field emitter array and correlation with theoretical models

Abstract

Improved fabrication and conditioning techniques for gated p-Si field emitter arrays (FEAs) (1×1mm2 in size with 50×50 emitters) greatly reduces the bulk damage and surface states. Consequently, only 0.9μA of the anode dark field-emission current was measured for 50V applied gate potential with a very low gate leakage current. At these low gate leakage currents, the transition between the tunneling-limited field-emission regime and the supply-limited saturation regime is clearly revealed in current-voltage plots. This transition is accompanied by a reduction in the anode current fluctuation. The standard deviation of the noise current drops from a few percent in the tunneling-limited regime to <1% in the supply limited regime at 50V. A photocurrent of 0.41mA was obtained for photoexcitation at 840nm wavelength. This corresponded to 40dB contrast ratio between the photocurrent and the dark current at room temperature. Additionally, our findings showed that surface states were fully depleted at low applied fields, the concentration of bulk defects was low and the area contributing to the dark current was confined to the emitter regions. In contrast, previously reported ungated Si field emitters had high concentrations of surface states and bulk defects. Furthermore, the contributing area to the dark current corresponded to the whole area of the device as opposed to only the emitter areas for a gated FEA. Photofield emission and dark current measurements from our gated p-Si FEA correlate well to theoretical models without requiring cooling to liquid-nitrogen temperatures.