The scattering mechanisms limiting mobility for low-dimensional charge carriers in a two-dimensional electron gas (2DEG) in undoped and doped AlGaN/AlN/GaN heterostructures with and without Si3N4 passivation are investigated. Hall effect measurements were carried out at temperatures from 1.8 K to 262 K and at a fixed magnetic field of 1 T. A good consistency was found between the calculated and the experimental results. The effects of in situ Si3N4 passivation on the 2DEG mobility are also discussed with majority scattering mechanisms. Interface-related parameters including quantum well width, deformation potential constant and correlation length of interface roughness were obtained from the fits of the analytical expressions of scattering mechanisms and compared for each heterostructure. After in situ Si3N4 passivation, we found that the effect of the interface roughness scattering, which was the dominant scattering mechanism at low temperatures, on the 2DEG mobility was more effective in undoped and doped AlGaN/GaN heterostructures. (C) 2016 Elsevier Ltd. All rights reserved.