We demonstrate the influence of misfit dislocations on the surface morphology and transport properties of In0.52Al0.48As/In0.75Ga0.25As/InP pHEMT structures grown by molecular beam epitaxy with InGaAs channel thicknesses that range from 20-35 nm. The differences in carrier scattering along different crystallographic directions for a given sample as determined by magnetotransport Hall bar measurements correspond to the asymmetric distribution of the orthogonal 60degrees misfit dislocations. The misfit dislocations introduce a well-defined roughness spectrum through the introduction of surface and interface steps and this roughness can be modeled in a straightforward fashion. This highly directional interface roughness is considered to be the scattering mechanism that is responsible for differences in mobility that are observed from sample to sample along different crystallographic directions. We believe that these results have implications for structures under the initial stages of strain relaxation and for metamorphic-based structures.