Targeted enrichment of 28Si thin films for quantum computing

We report on the growth of isotopically enriched Si-28 epitaxial films with precisely controlled enrichment levels, ranging from natural abundance ratio of 92.2% all the way to 99.99987% (0.832 x 10(-6) mol mol(-1 29)Si). Isotopically enriched Si-28 is regarded as an ideal host material for semiconducting quantum computing due to the lack of Si-29 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 Si-28. We switch the mass selective magnetic field periodically to control the Si-29 concentration. We develop a model to predict the residual Si-29 isotope fraction based on deposition parameters and measure the deposited film using secondary ion mass spectrometry (SIMS). The measured Si-29 concentrations show excellent agreement with the prediction, deviating on average by only 10%.