Optical hyperpolarization and detection of electron and nuclear spins of phosphorus donors in highly enriched 28Si

The linewidths of optical transitions associated with shallow impurities have been shown in recent studies to be much narrower in isotopically enriched 28Si as compared to natural Si. This is true of the no-phonon P donor bound exciton transition in 28Si, and using photoluminescence excitation spectroscopy, fine structure previously not seen in natural Si is revealed. Under a small external magnetic field, the P bound exciton transition shows a complicated structure consisting of six sets of doublets, with the doublet splitting being due to the splitting of the donor ground state by the hyperfine interaction between the spin of the donor electron and that of the 31P nucleus. The electron spin populations and the 31P nuclear spin populations can be determined by measuring the relative intensities of the hyperfine components in the photoluminescence excitation spectrum. Additionally, the predominant Auger recombination channel of these bound excitons is used to observe the same resolved hyperfine components in the photocurrent spectrum. By selectively ionizing donors in a specific hyperfine state via optical pumping of a specific hyperfine component, large polarizations of the electron and nuclear spins of 31P donors can be achieved at low field. Electron and nuclear polarizations of 90% and 76%, respectively, are obtained in less than a second, providing an initialization mechanism for qubits based on these spins, and enabling further ESR and NMR studies on dilute 31P in 28Si. A measurement of the homogeneous linewidth of the transitions associated with the 31P bound exciton, determined by spectral hole burning, is also presented. The observed 10 neV linewidth is only four times the limit set by the bound exciton lifetime.