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We have investigated the properties of single n- and p-type black silicon (b-Si) pillars with a height of 20 μ m under strong electric field and halogen lamp or laser illumination. For both type of b-Si pillar structures, I-V measurements revealed strong activation effects, which consisted in sudden current increases during the first up/down voltage sweeps. The maximum reproducible emission current from a single n-type b-Si pillar structure was about 15 μ A. A pronounced saturation region at 240 nA was observed for a single p-type b-Si pillar. The current fluctuation over time showed a standard deviation of 28% and 2.5% for n- and p-type single b-Si pillar structures, respectively. Optical switching under halogen lamp illumination resulted in at least 3 times higher saturation currents and showed a linear dependence of the FE current on the laser power.
Single gated p-type Si-tips with two different tip radii were fabricated. An emission current of 2.40 μA was measured for the sharp-edged tip at a voltage of 170 V. In contrast, a stable and reproducible emission behavior was observed with an increased tip radius resulting in a pronounced saturation region between 90 V and 150 V, but merely an emission current of 0.55 μA at 150 V. More remarkable is the stable emission behavior with fluctuation of ± 4 % during a measurement period of 30 minutes. The integral emission current in a homogeneous tip array (16 emitters) showed nearly the same I-V characteristics compared to the single tip and is therefore, most dominated by only a stable single tip in the array.
Nano Emitters on Silicon Pillar Structures generated by a Focused Electron Beam Induced Deposition
(2018)
Nano emitters were deposited by focused electron beam induced deposition of Trimethyl-(methylcyclopentadienyl)platinum(IV) on top of silicon pillars. The nano emitters were exactly positioned in the center on the top of up to four pillars of a quadratic arranged array of sixteen pillars with a pitch of 50 μm. Integral field emission measurements were performed in a diode configuration with a 50 μm mica spacer in a vacuum chamber at pressures of about 10 -9 mbar. The Fowler-Nordheim plots show a linear behavior, like expected for an n-type silicon material and a metal needle. The I-V measurement of the most promising sample shows an integral emission current up to 2 μm at a voltage of 600 V (12 MV/m) and an onset voltage for a current of 1 nA of about 300 V.
We investigated two different field emitter arrays consisting of 10×10 p-type and 10×10 undoped Au-coated high aspect ratio silicon tips. The I-V characterization of the p-type sample showed a pronounced saturation for voltages higher than 500 V and a maximum emission current of 39 nA. The metallized sample revealed a FN-like emission up to several μA. The metallized and the p-type sample operating below the saturation region showed high current fluctuations of ±16%. Whereas, the metallized sample with current regulation and the p-type sample in the saturation yielded a current stability of ±0.4% and ±0.3%, respectively. Investigations in the frequency domain revealed the for field emission typical 1/f-noise. By operating in the saturation region (p-type sample) or using an emission current regulation (metallized sample) the noise level was reduced by at least 20 dB. Finally, the p-type sample was illuminated by a light emitting diode to increase and modulate the emission current in the saturation region. The emission current was increased by a factor of 3.7 to 145 nA. With this configuration we emulated an unstable emission behavior and evaluated the performance of our emission current regulation circuit.
Photosensitivity of single lightly p-doped, highly p-doped, with an integrated p/n junction and intrinsic high-aspect-ratio (HAR) silicon tips was investigated in an ultra-high vacuum environment. The current-voltage characteristics (I-V) of the lightly doped p-type HAR tips showed a characteristic current saturation at around 10-12 nA, whereas the HAR Si tips with p/n junction showed similar saturation phenomena, however, at much smaller current values starting at ~20-30 pA. Optical switching under a halogen lamp illumination resulted in at least 2-4 times higher saturation currents and showed a linear dependence between the illumination power and the FE current, for both types of structures. In case of the highly p-doped HAR tips optical current switching effects, i. e. current saturation, were observed at rather low current levels 1-2 pA. Intrinsic HAR Si-tips showed relative unstable field emission behavior without a clear evidence of the photosensitivity.