In contrast to the case of acoustic vibrations where the perturbation Hamiltonian is proportional to the derivative of the atomic displacement, the perturbation Hamiltonian for the optical modes is assumed to be proportional to the atomic displacement. Due to the quite flat dispersion curve, the energy associated with optical phonons is assumed to be constant. In this case, the phonon occupation number Nop is independent on the phonon wave vector. Since the scattering arises from the band edge variation induced by optical phonons, we can rely on the considerations done for deformation potential scattering for acoustic phonons. Assuming an isotropic deformation potential, the coupling coefficient of its interaction potential can be written as
|
| (5.28) |
The scattering rate caused by optical phonons is given by (see Appendix B.3)
 | (5.29) |