  The authors have applied positron annihilation spectroscopy to study the
effect of different growth conditions on vacancy formation in In- and N-polar
InN grown by plasma-assisted molecular beam epitaxy. The results suggest that
the structural quality of the material and limited diffusion of surface adatoms
during growth dictate the In vacancy formation in low electron-density undoped
epitaxial InN, while growth conditions and thermodynamics have a less important
role, contrary to what is observed in, e.g., GaN. Further, the results imply
that in high quality InN, the electron mobility is likely limited not by
ionized point defect scattering, but rather by threading dislocations.
