  Infrared Detectors based on a Quantum Cascade have been proposed to suppress
the dark current which is identified as a limiting factor in Quantum Well
Infrared Photodetectors. Those detectors have been mostly designed for the
3-5um and 8-12um range of wavelength. For detector operating in the THz range a
complete change of regime of transport is expected since the photon energy is
lower than the Longitudinal Optical (LO) phonon energy. Using a two dimensional
code of transport we have identified Interface Roughness (IR) as the key
interaction in such a structure. We have used scanning transmission electron
microscopy (STEM) to evaluate the IR parameters (magnitude of the roughness and
mean distance between defects) instead of the classical mobility measurements.
Finally, we used these parameters to study their influence on the resistance of
the device.
