  The injection of spin polarized electrons from ferromagnetic metals (Fe and
Co) into gallium nitride (GaN) via scanning tunneling microscopy (STM) is
demonstrated. Electrons from STM tips are injected into the semiconductor. Net
circular polarization of the emitted light is observed, which changes sign on
reversal of the magnetization of the tip. The polarization is found to be in
qualitative agreement with that expected from considerations based on the
splitting of the valence bands due to spin-orbit coupling and the crystal field
splitting corresponding to the wurtzite structure, and the magnitude of the
spin polarization from the ferromagnetic metal. We find a lower bound for the
spin injection efficiency of 25%, corresponding to a net spin polarization in
the semiconductor of 10%. This is the largest reported value for a room
temperature measurement of spin injection into semiconductors in air.
