Anisotropy in the quantum lifetime in AlGaN/GaN heterostructures

Magnetoresistance measurements were performed on van der Pauw shaped AlGaN/GaN heterostructures grown on either sapphire or silicon carbide. These measurements revealed the presence of Shubnikov-de Haas oscillations. However, the amplitude of the oscillations originating from perpendicular van der Pauw positions were not isotropic. This anisotropy varied from sample to sample and within a sample its magnitude changed with the carrier density which was modulated by illumination as it induced a persistent photocurrent. The results of this study suggest the anisotropy is either a manifestation of electron density inhomogeneities and/or an indication of a nonuniform scattering mechanism arising from nonuniform interface roughness.