Electron Transport in Nanocrystalline Si Based Single Electron Transistors

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.

Charge injection and trapping in silicon nanocrystals

“…While electronic transport through single nanocrystals shows strong single-electron charging effects at low temperatures, 8 it is not clear if this occurs in large numbers of nanocrystals. At high bias, it is possible to observe electron emission from thin films of nanocrystals.…”

“…Single-electron or quantum confinement effects could then lead to a discrete density of states in the well. 4,8 If the higher charge number states, closer to the top of the potential barrier, were delocalized then only a few localized ͑trapping͒ states would exist on a nanocrystal. This would limit the number of carriers trapped in the well and explain our similarity between N t and N nc .…”

Nanofabrication by advanced electron microscopy using intense and focused beam∗

“…That of the location depends mainly on the stability of the specimen stage, which is on the order of 0.1 nm over a few seconds, and that of the size depends only on the deposition time, which is accurately controlled by a computer. Some studies have been carried out to realize quantum devices and other types of devices by EBID [5,53,54]. EBID deposits can also be used as masks for ion milling to fabricate fine structures [55][56][57].…”

Single-electron transistor based on a silicon-on-insulator quantum wire fabricated by a side-wall patterning method

“…17 Moreover, the slight variation of the oscillation period reflects not only the depletion width varied by the depletion gate bias 18 but also the discrete electron energy level separation. 19 SETs based on doped polysilicon nanowires also show a change of a factor of a few times at the same device. 20 In our system, however, the polysilicon side-wall depletion gate wraps the Si channel three dimensionally, and the top control gate becomes further separated from the Si wire than the side-wall depletion gates.…”