Interface and confined phonons in stepped quantum wells

The simple symmetric and antisymmetric interface-phonon modes of a square quantum well do not occur in an asymmetric quantum well. The presence of extra materials and interfaces affects the potentials of the interface (IF) phonons in addition to the widely recognized effect on the electronic wave functions. Our `stepped' quantum well structures have phonon modes (potentials) localized at the well/step interface, so these structures have 8 confined-LO (LC) phonon modes and 10 IF phonons. We calculate the non-trivial dispersion of the IF phonons for increasing asymmetry (step height); classify the resulting phonon potentials into `even-like', `odd-like', and `centred'; and explain the strongest electron-IF-phonon scattering processes in terms of their matrix elements. The result is that the LC scattering rates increase with increasing asymmetry, whilst the IF rates decrease.