Growth of ultra-thin fluoride heterostructures on Ge(1 1 1) for quantum devices

Epitaxial growth of fluoride quantum well structure of Ca x Sr 1− x F 2/CdF 2/Ca x Sr 1− x F 2 on Ge(1 1 1) is investigated. The two-step growth method was found to be useful for growth of the initial Ca x Sr 1− x F 2 layer on Ge(1 1 1) in which Ca x Sr 1− x F 2 was deposited at room temperature followed by in situ annealing for solid phase epitaxy. The quantum well structures composed of triple fluoride layers on Ge(1 1 1) substrates were superior to conventional ones grown on Si(1 1 1) substrate, due to the less chemical reactivity of CdF 2 with Ge than that with Si.