Dynamic Nuclear Polarization of 29Si Nuclei Induced by Li and Li--O Centers in Silicon

Dynamic nuclear polarization (DNP) of 29Si nuclear spins induced by saturation of electron paramagnetic resonance (EPR) transitions of lithium-related centers in float zone (FZ) grown silicon is reported. Both isolated Li and Li--O complex centers showed strong EPR absorption lines in the temperature range 3.4--10 K and led to very efficient orientation of 29Si nuclear spins. The temperature dependence and time constant of 29Si DNP are investigated in detail. The 29Si DNP of 0.72% was achieved at 3.4 K by excitation of the Li--O forbidden EPR transition under illumination, corresponding to a ${\sim}352$ fold increase with respect to the thermal equilibrium polarization.