Structure analysis of GaN thin film with inversion domains by high voltage atomic resolution microscopy

The atomic structures and surface morphologies of three types of GaN films were investigated by high voltage atomic resolution microscopy (HVARM). By HVARM, each atomic column of Ga and N could clearly be resolved and the polarity of the film and inversion domains could be directly determined. The GaN film was grown on a sapphire substrate by molecular beam epitaxy (MBE) after nitridation of the sapphire surface. Inversion domains (IDs) crossed the whole film to the surface and made small pyramids on the surface. The small pyramids had Ga-polarity and the rest had N-polarity. A GaN film with In exposure during film growth had an almost Ga-polarity flat surface. In exposure process reduced the density of inversion domains that have a N-polarity. While a GaN film grown on an AlN buffer layer was unipolar, with a Ga-polarity. HVARM observation revealed that the density of the IDs determine the qualities and the polarity of the film.