Optical orientation of nuclei in nitrogen alloys GaAsN at room temperature

The intensity and giant circular polarization of edge luminescence in a longitudinal magnetic field have been measured in nitrogen alloys GaAsN under circularly polarized pumping. It has been found that these dependences are shifted with respect to zero field by a value $B_{\textrm{eff}}$. The magnitude of the internal field $B_{\textrm{eff}}$ increases with the pumping intensity and reaches saturation ($\approx250$ G) at large excitation densities. The saturation of the B eff field with growth of pumping indicates that this is a field of nuclei, polarized dynamically due to hyperfine interaction with optically oriented deep paramagnetic centers, rather than a field of exchange interaction created on the center by spin-polarized photo-excited conduction electrons. The short time of nuclear polarization by electrons ($<15\,\mu$s), measured under modulation of circular polarization of the exciting light with high frequency, points to a small number of nuclei undergoing hyperfine interaction with an electron localized at a center.