Targeted enrichment of (28)Si thin films for quantum computing

We report on the growth of isotopically enriched (28)Si 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 (28)Si is regarded as an ideal host material for semiconducting quantum computing due to the lack of (29)Si 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 (28)Si. We switch the mass selective magnetic field periodically to control the (29)Si concentration. We develop a model to predict the residual (29)Si isotope fraction based on deposition parameters and measure the deposited film using secondary ion mass spectrometry (SIMS). The measured (29)Si concentrations show excellent agreement with the prediction, deviating on average by only 10%.