Hall effect measurements on undoped Al0.2Ga0.8N/AlN/GaN/AlN heterostructures grown on 6H-SiC substrates were carried out as a function of the temperature (30-300 K) and magnetic field (0-1.4 T). Measurements were carried out under dark and after-illumination conditions. After the dark measurements, the samples were illuminated with a blue light emitting diode for 30 min, and then the same measurements were carried out for the after-illumination condition. The magnetic field dependent Hall results were analyzed and the 2DEG contribution was found using the quantitative mobility spectrum analysis (QMSA) technique. A self-consistent scattering analysis between the dark and illuminated conditions was implemented. The importance of this implementation was to find an indirect way to locate more certain fit parameters, such as interface roughness parameters and the background impurity value, which cannot be found using dark measurement data alone.