The Effect of Gap Width on Field Emission Properties of Lateral Silicon Diodes

Abstract:

A simple method for fabricating lateral Si diodes with various gap widths were designed using the special properties of anisotropic TMAH wet etching and local anodic oxidation. The electrical performance of lateral diode was characterized using an HP4156c semiconductor parameter analyzer (SPA300HV, Agilent) at room temperature in a vacuum environment lower than 10^-8 Torr. The emission current from the silicon emitter cathode was measured as a function of the applied anode voltage. The effect of changing the anode-cathode gap was observed in the I-V characteristics, with a distinct reduction in the device turn-on with a decrease in the gap. For narrowed nanogaps from 55 nm to 35 nm, the turn-on voltage was decreased from 21 V to 16 V. Values of field enhancement factor β and emitting area A for different gap width were measured using Fowler-Nordheim plot. Our results indicate that β reduces and emitting area increases with increasing of gap width.

• Periodical: Advanced Materials Research (Volume 1109)
• Pages: 505-508
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.1109.505
• Online since: June 2015
• Authors: J. Rouhi*, Mohd Husairi Fadzilah Suhaimi, Kevin Alvin Eswar, M.H. Mamat, Salman A.H. Alrokayan, Haseeb A. Khan, M. Rusop
• Keywords: Field Emission Properties, Fowler-Nordheim Plot, Lateral Silicon Diodes, Local Anodic Oxidation

References

[13] Fig. 1: (a) AFM and (b) FESEM images of silicon diode with 35 nm gap width The lateral diodes are varied only in gap width; the emitter geometries are controlled and are kept constant during the electrical measurement. The radius curvature of the apex is set to 60 nm. The two devices with different gap widths of 35 and 55 nm were separately considered for FE under similar vacuum environments of lower than 10–9 Torr [10, 14]. The I–V characteristic was determined for each device and the results were compared. The lateral emitter was designed to have a high geometrical aspect ratio with a small curvature radius of the emitter tip. The emission current of the various emitters is related to the modified F–N equation.

[15] Log (I/V2) = log (a) + 0. 434 (- b/V) (1) where , φ is work function in eV, A is emitting area in cm2and β is the field enhancement factor (in cm–1), which depends on electrode shape. Fig. 2: (a) I-V curves of the field emission for different distance d (b)Corresponding F-N plots The effect of varying the gap width is reflected in the I–V characteristics, with a clear reduction in the turn-on voltage as the anode–cathode gap decreases (Fig. 2). The Si lateral diode with 55 nm and 35 nm gap width exhibits turn-on voltages of 21 and 16 V, respectively. The I–V characteristics of the devices are graphically presented in Fig. 2a. The anode current of approximately 6 µA was obtained at 32 to 33 V for the 35 and 50 nm gap widths, respectively. These results show that the emission current rapidly increases after the turn-on voltage is applied. The emission current from the lateral emitters is consistent with the F–N behavior, as shown in Fig. 2b. When the gap width between the emitter and the anode electrode decreases, the electric field increases . The high electric field decreases the potential barrier at the surface; thus, the electrons can tunnel from inside the semiconductor to the vacuum [5, 16]. For narrowed nano-gaps from 55 to 35 nm, therefore, the turn-on voltage decreases from 21 to 16 V. The value of β was determined from the F–N plot slope. The β and A values for a gap width of 55 nm are 0. 58 × 107 cm–1 and 3. 35 × 10–18 cm2, respectively (Fig. 2b). Our results indicate that β decreases and the emitting area increases with increasing gap width. Conclution Round-tip emitters with nanoscale gaps of 35 to 55 nm were fabricated by advanced nanofabrication technology based on AFM nanolithography and wet etching. I-V characteristics show that the gap width of electrodes is effective parameters in lateral silicon field emission diodes. For the narrowed nano-gaps from 55 nm to 35 nm, the turn-on voltage decreased from 21 V to 16 V. Refrences.

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