Electron Transport in Nanocrystalline Si Based Single Electron Transistors

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Abstract
Electron transport has been studied by measurement and simulation of single electron transistors based on nanocrystalline silicon (nc-Si). Nanocrystalline silicon is formed in the gas phase of the SiH4 plasma cell by the coalescence of radicals. Digital chemical vapor deposition [CVD] technique using pulsed gas in the plasma is effective to obtain highly uniform Si quantum dots with an average size of 8 nm and dispersion of 1 nm. Single electron transistors have been successfully fabricated by deposition of nc-Si on top of heavily doped silicon nanoelectrodes with a gap of 15 nm which allows the study of electron transport through two or three nanocrystals. Coulomb blockade and Coulomb oscillations are observed in these devices at various temperatures, including room temperature. The observed Coulomb diamond structure is not as simple as in the case of metallic islands. With increasing gate voltage, the spacing between oscillation peaks decreases and the Coulomb diamonds reduce in size. These observations are explained on the basis of electron transport through a quantum dot with an energy gap between the highest occupied and the lowest unoccupied electron states. Modeling of such a system can reproduce measured electrical characteristics. The unequal spacing of gate oscillations and the reduced size of Coulomb diamonds are due to the interplay of Coulomb charging energy and the energy separation between the quantized energy levels.