Anisotropic damping of longitudinal optical phonon-plasmon coupling modes of InN films

The energy broadenings of the higher energy branch of the longitudinal optical (LO) phonon-plasmon coupling modes for E-1(LO) and A(1)(LO) are analyzed for InN films by infrared reflectance and spectroscopic ellipsometry. Larger broadening for the vibration parallel to c of A(1)(LO)-plasmon coupling is found with the decrease in electron density. This phenomenon is caused by the plasmon lifetime anisotropy, and is attributed to the reduction in crystal defects causing isotropic carrier scattering and the remaining of defects along the c axis such as threading dislocations and columnar grain boundaries. (C) 2008 American Institute of Physics.