A compact, UHV ion source for enriching 28Si and depositing epitaxial thin films
Ke Tang, Hyun Soo Kim, Aruna N. Ramanayaka, David S. Simons, Joshua M. Pomeroy
An ultra-high-vacuum (UHV) compatible Penning ion source for growing pure, highly enriched 28Si epitaxial thin films is presented. Enriched 28Si is a critical material for quantum information due to the elimination of nuclear spins and, in some cases, must be grown by low temperature MBE (molecular beam epitaxy), e.g., STM hydrogen lithography based devices. Traditional high- purity physical vapor methods typically deliver a very small fraction of source material onto the target substrate making the cost for use with highly enriched source materials very expensive. Thus, directed beam sources provide an efficient alternative. This UHV Penning source uses all metal or ceramic parts and a removable electromagnet to allow bake-out and uses commercial (natural isotope abundance) silane gas (SiH4), an inexpensive source material. High enrichment levels up to 99.99987 % (8.32 × 10-7 mol/mol 29Si) and high chemical purity of 99.965 % are shown without post-processing (post-annealing can substantially improve the purity). We present and discuss the discharge properties of this new source, the ion mass spectrum when coupled to our mass filter, and the secondary ion mass spectroscopy (SIMS) of the grown films.