Targeted enrichment of ²⁸Si thin films for quantum computing

We report on the growth of isotopically enriched ²⁸Si epitaxial films with precisely controlled enrichment levels, ranging from natural abundance ratio of 92.2% all the way to 99.99987% (0.83 × 10^-6 mol mol^{-1 29}Si). Isotopically enriched ²⁸Si is regarded as an ideal host material for semiconducting quantum computing due to the lack of ²⁹Si nuclear spins. However, the detailed mechanisms for quantum decoherence and the exact level of enrichment needed for quantum computing remain unknown. Here we use hyperthermal energy ion beam deposition with silane gas to deposit epitaxial ²⁸Si. We switch the mass selective magnetic field periodically to control the ²⁹Si concentration. We develop a model to predict the residual ²⁹Si isotope fraction based on deposition parameters and measure the deposited film using secondary ion mass spectrometry (SIMS). The measured ²⁹Si concentrations show excellent agreement with the prediction, deviating on average by only 10%.