  A general model for treating the effects of three dimensional interface
roughness (IFR) in layered semiconductor structures has been derived and
experimentally verified. Configurational averaging of the IFR potential
produces an effective grading potential in the out-of-plane direction, greatly
altering the energy spectrum of the structures. IFR scattering self-energy is
also derived for the general case; when IFR is strong, its scattering effect is
shown to dominate over phonon interaction and impurity scattering. When applied
to intersubband transitions, the theoretical predictions explain the
experimental observation of the anomalous energy shift and unusual broadening
of the ISB transitions in III-Nitride thin-layered superlattices.
