We achieved the amazing improvements of the structural and electrical properties of GaN heteroepitaxial layers grown by molecular beam epitaxy on sapphire substrate. The improvements were carried out by the controlling of the lattice polarity due to exposure to a small amount of In flux during GaN epiaxial growth. The lattice polarities of GaN samples were confirmed by Coaxial Impact Collision Ion Scattering Spectroscopy (CAICISS) technique. By the structural and electrical evaluation of the GaN epitaxial samples, it is clarified that (0001) Ga-polarity GaN is superior compared with (000-1) N-polarity GaN. Hall measurement revealed that more than one order higher mobility of Ga-polarity layers compared with N-polarity layers. These results give the advances in the growth of high quality nitride films by MBE for device applications.