Gap distance dependence on field emission at the nanogap between silicon cleavage surfaces

Abstract

In this study, we developed a model of field emission at a vacuum nanogap composed of semiconductor electrodes and conducted numerical calculations to evaluate its field emission characteristics. The current at the silicon nanogap was also measured, and the results were compared with the calculated results. Large-area vacuum nanogaps are expected to be used for highly efficient room-temperature thermionic power generation owing to their good thermal insulation, and their electrical conduction of tunneling current is sufficient for practical use. Because vacuum nanogaps should be parallel and smooth with a large area, we proposed and examined the use of cleavage to fabricate nanogaps in single-crystal materials. A nanogap with a nominal area of 26.5 μm2 was fabricated in a microelectromechanical device to evaluate its properties, and the model was used for the analysis. The calculated current–voltage characteristics of the semiconductor nanogap of both n-type and p-type silicon were affected by the bandgap and the presence of carriers, i.e., electrons and holes. Moreover, the Fowler–Nordheim plot was confirmed to be valid for semiconductor nanogaps based on the calculated results. We proposed an effective work function that compensates for the discrepancy between semiconductor nanogaps and the Fowler–Nordheim theory and enables a more accurate analysis. Field-emission currents flowing through a 1.1 nm nanogap were measured and matched with the calculated results by adjusting the field enhancement factor and emission area. The model developed and confirmed experimentally in this work will be helpful in examining field emissions at semiconductor nanogaps.