We show that single-electron transport through a single dopant can be achieved even in a random background of many dopants without any precise placement of individual dopants. First, we observe potential maps of a phosphorus-doped channel by low-temperature Kelvin probe force microscopy, and demonstrate potential changes due to single-electron trapping in single dopants. We then show that only one or a small number of dopants dominate the initial stage of source-drain current vs gate voltage characteristics in scaled-down, doped-channel, field-effect transistors.
Detection of individual dopants in the thin silicon layer using Kelvin Probe Force Microscopy is presented. The analysis of the surface potential images taken at low temperatures (13K) on n-type and p-type samples reveals local potential fluctuations that can be attributed to single phosphorus and boron atoms, respectively. Results are confirmed by simulation of surface potential induced by dopants and by the back gate voltage dependence of the measured potential.
Single-electron transfer operation in single-gated one-dimensional quantum dot arrays is investigated statistically from the viewpoint of robustness against parameter fluctuations. We have found numerically that inhomogeneous quantum dot arrays as formed in doped nanowires exhibit single-electron transfer in a wide range of parameters. This confirms our frequent experimental observation of single-electron transfer in doped-nanowire field-effect transistors. The most important result in this work is that three-dot arrays with small-large-small dot size distribution always allow single-electron transfer even under dot size fluctuations. This structure is, we believe, most promising for fabricating devices with high immunity against structural fluctuations in nanometer-scale. Finally, based on these findings, we propose methods to fabricate high-yield single-electron transfer devices.
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