Modification of the tunneling barrier in a nanocrystalline silicon single-electron transistor

Single-electron transistors (SETs) consisting of side-gated nanowires fabricated in 20-nm-thick hydrogenated nanocrystalline silicon films prepared at 300 °C have been investigated. It is found that if the nanowire width is <30 nm the conductivity increases with oxidation of the nanowires at 650 °C and decreases with oxidation at 750 °C. SETs oxidized at 750 °C exhibit single-electron charging effects at room temperature. Secondary ion mass spectroscopy suggests that the tunneling barriers are silicon sub-oxide formed by oxygen diffusion through the grain boundaries, and that oxidation from the sidewalls of the nanowire plays an important role in establishing the tunnel barrier.