Isotopically Enriched Layers for Quantum Computers Formed by ²⁸Si Implantation and Layer Exchange

²⁸Si enrichment is crucial for production of group IV semiconductor-based quantum computers. Cryogenically cooled, monocrystalline ²⁸Si is a spin-free, vacuum-like environment where qubits are protected from sources of decoherence that cause loss of quantum information. Currently, ²⁸Si enrichment techniques rely on deposition of centrifuged SiF₄ gas, the source of which is not widely available, or bespoke ion implantation methods. Previously, conventional ion implantation into ^naturalSi substrates has produced heavily oxidized ²⁸Si layers. Here we report on a novel enrichment process involving ion implantation of ²⁸Si into Al films deposited on native-oxide free Si substrates followed by layer exchange crystallization. We measured continuous, oxygen-free epitaxial ²⁸Si enriched to 99.7%. Increases in isotopic enrichment are possible, and improvements in crystal quality, aluminum content, and thickness uniformity are required before the process can be considered viable. TRIDYN models, used to model 30 keV ²⁸Si implants into Al to understand the observed post-implant layers and to investigate the implanted layer exchange process window over different energy and vacuum conditions, showed that the implanted layer exchange process is insensitive to implantation energy and would increase in efficiency with oxygen concentrations in the implanter end-station by reducing sputtering. Required implant fluences are an order of magnitude lower than those required for enrichment by direct ²⁸Si implants into Si and can be chosen to control the final thickness of the enriched layer. We show that implanted layer exchange could potentially produce quantum grade ²⁸Si using conventional semiconductor foundry equipment within production-worthy time scales.