Properties of GaN on different polarity buffer layers by hydride vapour phase epitaxy

This paper reports on N-, mixed-, and Ga-polarity buffer layers aregrown by molecular beam epitaxy (MBE) on sapphire (0001) substrates,with the GaN thicker films grown on the buffer layer with differentpolarity by hydride vapour epitaxy technique (HVPE). The surfacemorphology, structural and optical properties of these HVPE-GaNepilayers are characterized by wet chemical etching, scanningelectron microscope, x-ray diffraction, and photoluminescencespectrum respectively. It finds that the N-polarity film is unstableagainst the higher growth temperature and wet chemical etching, whilethat of GaN polarity one is stable. The results indicate that thecrystalline quality of HVPE-GaN epilayers depends on the polarity ofbuffer layers.