Native defects in InxGa1-xN (x = 0.06-0.14) grown by metal organic chemical vapor deposition were studied using a monoenergetic positron beam. Measurements of Doppler broadening spectra of the annihilation radiation as a function of incident positron energy for InxGa1-xN showed that vacancy-type defects were introduced with increasing InN composition, and the major defect species was identified as complexes between a cation vacancy and a nitrogen vacancy. The concentration of the divacancy, however, was found to be suppressed by Mg doping. The momentum distribution of electrons at the InxGa1-xN/GaN interface was close to that in defect-free GaN or InxGa1-xN, which was attributed to localization of positrons at the interface due to the built-in electric field, and to suppression of positron trapping by vacancy-type defects. We have also shown that the diffusion property of positrons is sensitive to an electric field near the InxGa1-xN/GaN interface.