We present a systematic study of various ways (top gates, local doping,substrate bias) to fabricate and tune multi-dot structures in silicon nanowiremultigate MOSFETs (metal-oxide-semiconductor field-effect transistors). Thecarrier concentration profile of the silicon nanowire is a key parameter tocontrol the formation of tunnel barriers and single-electron islands. It isdetermined both by the doping profile of the nanowire and by the voltagesapplied to the top gates and to the substrate. Local doping is achieved withthe realisation of up to two arsenic implantation steps in combination withgates and nitride spacers acting as a mask. We compare nominally identicaldevices with different implantations and different voltages applied to thesubstrate, leading to the realisation of both intrinsic and doped coupled dotstructures. We demonstrate devices in which all the tunnel resistances towardsthe electrodes and between the dots can be independently tuned with the controltop gates wrapping the silicon nanowire.
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