Direct observation of the donor nuclear spin in a near-gap bound exciton transition: ³¹P in highly enriched ²⁸Si

We report on ultrahigh resolution studies of the bound exciton states associated with the shallow acceptor B and the shallow donor P in highly enriched S 28 i using a tuneable single frequency laser to perform photoluminescence excitation spectroscopy. The linewidths and fine structure of the transitions, which were too narrow to be resolved previously using an available photoluminescence apparatus, are now fully revealed. The P bound exciton transition shows a complicated additional structure, which the Zeeman spectroscopy demonstrates to be a result of the splitting of the donor ground state by the hyperfine interaction between the spin of the donor electron and that of the P 31 nucleus. The P 31 nuclear spin populations can thus be determined, and hopefully modified, by optical means. The predominant Auger recombination channel of these bound excitons is used to observe the same resolved hyperfine transitions in the photocurrent spectrum. This demonstrates that donors in specific electronic and nuclear spin configurations can be selectively photoionized. Possible applications of these results to quantum computing and quantum information systems are discussed.