N-polarity GaN on sapphire substrate grown by MOVPE

N-polar GaN was grown on (0001) sapphire using two-step growth technique by MOVPE. In the growth, the key points were the controlling of the density of nuclei in a buffer layer and promoting lateral growth at high temperature. The grown GaN films had mirror-like smooth surfaces and were proved to have N-polarity using convergent-beam electron diffraction and coaxial impact-collision ion spectroscopy. The FWHM of this GaN in the ω-scan was also much narrower than the previous reports. The density of threading dislocations was much less than for usual Ga-polar GaN grown with a GaN or Aln buffer layer by MOVPE and MBE. In PL at room temperature, the strong edge emission was observed as Ga-polarity. The p-type conduction in Mg-doped GaN was also realized by the same methods as for Ga-polarity.