Anisotropy of the photo-induced persistent internal polarization of a semiconductor
A theory is presented for the anisotropy of the persistent internal polarization, i.e. for its dependence on the angle between the applied electric field and thec-axis as it has been observed with Li-doped ZnO crystals. Starting point is a Boltzmann equation with anisotropic collision and capture terms. From it, a relation is derived between the ratios of the polarizations for electric fields perpendicular and parallel to thec-axis and of the effective capture cross sections for photo electrons moving parallel and perpendicular to thec-axis.