where r is the scattering parameter and depends on the scattering mechanism. For example, r = -1/2 represents acoustic deformation potential scattering, whereas r = 1/2 represents polar optical phonon scattering. In cases where carrier transport can be described by a parabolic band, using the power law form of ⌧ (E) in Eq. ( ), the transport coe cients can be recast as,