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The use of etched registration markers to make four-terminal electrical contacts to STM-patterned nanostructures

We demonstrate the use of etched registration markers for the alignment of four-terminal ex situ macroscopic contacts created by conventional optical lithography to buried nanoscale Si:P devices, patterned by hydrogen-based scanning tunnelling microscope (STM) lithography. Using SiO2 as a mask we are able to protect the silicon surface from contamination during marker fabrication and can achieve atomically flat surfaces with atomic-resolution imaging. The registration markers are shown to withstand substrate heating to ∼1200 °C and epitaxial overgrowth of ∼25 nm Si. Using a scanning electron microscope to position the STM tip with respect to the markers, we can achieve alignment accuracies of ∼100 nm, which allows us to contact buried Si:P structures. We have applied this technique to fabricate P-doped wires of different widths and measured their I–V characteristics at 4 K, finding ohmic behaviour down to a width of ∼27 nm.