Optical Hyperpolarization of Phosphorus Donor Nuclei and Bound Exciton Capture Rates in Isotopically Purified Silicon*

We present optical pumping experiments on phosphorus defects in isotopically purified (²⁸Si) silicon at low temperatures and high magnetic fields. Using a combination of above bandgap laser light along with radio frequency saturation and control fields we study the optical dynamical nuclear polarization (DNP) mechanism and measure the rates of Auger ionization processes associated with bound exciton recombination events. We conclude that the dominant DNP mechanism under our experimental conditions is phononic. This has implications both for optimization of devices utilizing the extremely long coherence times of phosphorus nuclei in isotopically purified silicon, and providing a technique for measuring location dependent, frequency specific information of elastic waves in silicon devices.