15.Kk 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.
To establish an accurate determination technique for the polarity of InN by convergent-beam electron diffraction (CBED), we clarified the influence of the electron incidence direction, film thickness, and the temperature factor B on CBED patterns by simulation. The electron incidence direction of [11¯00] and a film thinner than 50nm were found to be preferable for easy and reliable polarity determination. Using an InN film grown on a (0001¯) GaN template on (0001) sapphire by metalorganic vapor-phase epitaxy, observation of the CBED pattern in the thin region of the film was confirmed from the simulation result. This InN film was clearly determined to have N polarity and the value of B was estimated to be less than 2.0Å2.
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