Coaxial Impact Collision Ion Scattering Spectroscopy (Caiciss) Analysis For The Polarity Conversion Of Gan Films Grown On Nitrided Sapphire Substrates

CAICISS characterization was carried out on the polarities of GaN films grown on sapphire substrates, which were modified with nitridation and subsequent TMAl flow prior to low temperature buffer layer deposition. The TMAl preflow was intentionally introduced to cover the nitridated sapphire surface with Al layers. CAICISS results showed that the polarity of GaN epilayer could be successfully converted from N-polar to Ga-polar by a TMAl preflow of 5 mu mol/min at 550 degreesC for more than 5 seconds. Optical microscope observation also confirmed that GaN surface was changed from hexagonal morphologies to smooth and featureless ones. A "two monolayers of Al" model was tentatively proposed to explain the polarity conversion mechanisms.