Light-induced nuclear quadrupolar relaxation in semiconductors

Light excitation of a semiconductor, known to dynamically polarize the nuclear spins by hyperfine contact interaction with the photoelectrons, also generates an intrinsic nuclear depolarization mechanism. This relaxation process arises from the modulation of the nuclear quadrupolar Hamiltonian by photoelectron trapping and recombination at nearby localized states. For nuclei near shallow donors, the usual diffusion radius is replaced by a smaller, quadrupolar, radius. If the light excitation conditions correspond to partial donor occupancy by photoelectrons, the nuclear field experienced by electrons trapped at shallow donors can be decreased by more than 1 order of magnitude.