Dynamic polarization filtering in anisotropically strained M-plane GaN films

The dynamic optical polarization filtering for anisotropically strained M-plane GaN films on LiAlO2 is investigated by pump and probe spectroscopy. Due to a very large polarization anisotropy in the absorption coefficient, these films exhibit an intrinsic polarization filtering, which appears as a rotation of the polarization vector after transmission of linearly polarized light through the film. For dynamic filtering, the polarization rotation is controlled by the pump, since the photoexcited carriers remove the intrinsic linear dichroism by selective bleaching of the anisotropic absorption. The dynamic behavior of the polarization rotation is mainly determined by the redistribution of holes between the two uppermost valence bands and by the recombination time. The latter is comparable to the measured decay time of the dynamic rotation of about 15 ps. For M-plane GaN films, the maximum dynamic rotation reaches 35 degrees, while the maximum static polarization rotation is about 40 degrees. (c) 2005 American Institute of Physics.