Abstract
High quality GaN film with a smooth surface free from hillocks , pits and cracks can be grown epitaxially on a sap-phire substrate by metalorganic vapor phase epitaxy (MOVPE) usingd a thin AlN buffer layer. The initial growth stage of GaN film with and without the buffer layer is studied in detail. It is found that the most essential role of the buffer layer is ( I ) supply of the nucleation centers with the same crystal orientation as the substrate and (2) promotion of the lateral growth of GaN due to the decrease in an interfacial free energy between the substrate and the GaN film.
