From the viewpoint of high- (room-) temperature operation of donor-based single-electron transistors, we make a comparative study of nano-scale silicon-on-insulator transistors with phosphorus-doped channels for two dopant concentrations: ND ≈ 1.0×10^18 and 2.0×10^20 cm-3. We experimentally show that the high-ND devices can provide room-temperature single-electron tunneling operation owing to a large tunnel-barrier height, while operation temperature is limited to about 100 K for the low-ND devices. Numerical simulations of random donor-atom distributions indicate that donor clustering plays a dominant role in the formation of quantum dots, and suggests that clusters comprising of more-than-three donors are responsible for room-temperature operation.

Electron transport through a few-donor cluster flanked by acceptors is studied by first-principles and semi-empirical simulations in gated Si-nanowire transistors with n + electrostatically-doped source/drain. Local density-of-states spectra are probed by electrical characteristics at room temperature for clarifying modifications induced by acceptor-atoms on the energy states of the few-donor cluster. It is found that acceptor-atoms located between the few-donor cluster and the leads mainly shift the cluster potential, introducing a minor distortion to its energy spectrum. The results change only weakly as the acceptor-atoms are moved towards the Si nanowire surface, and systematically depend on the number of acceptors.

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