Highly 28si Enriched Silicon by Localised Focused Ion Beam Implantation

Solid-state spin qubits within silicon crystals at mK temperatures show great promise in the realisation of a fully scalable quantum computation platform. Qubit coherence times are limited in natural silicon owing to coupling to the Si-29 isotope which has a non-zero nuclear spin. This work presents a method for the depletion of Si-29 in localised volumes of natural silicon wafers by irradiation using a 45 keV Si-28 focused ion beam with fluences above 1 x 10(19) ions cm(-2). Nanoscale secondary ion mass spectrometry analysis of the irradiated volumes shows residual Si-29 concentration down to 2.3 +/- 0.7 ppm and with residual C and O comparable to the background concentration in the unimplanted wafer. After annealing, transmission electron microscopy lattice images confirm the solid phase epitaxial re-crystallization of the as-implanted amorphous enriched volume extending over 200 nm in depth.