Threading dislocation reduction in three-dimensionally grown GaN islands on Si (111) substrate with AlN/AlGaN buffer layers

Three-dimensional GaN island growth without any masks was first introduced under high pressure in metalorganic chemical vapor deposition after the growth of AlN and AlGaN buffer layers on Si ( 111) substrate, followed by two-dimensional GaN growth to form a continuous GaN film with improvement of the crystalline quality and surface smoothness. X-ray diffraction and cross-sectional scanning transmission electron microscopy analyses show that a high-quality GaN film can be achieved by bending of edge threading dislocations (TDs) and the formation of dislocation half-loops. It is observed that most of edge TDs bend 90 degrees from the growth direction along c-axis, whereas mixed TDs bend about 30 degrees towards the inclined sidewall facets of the islands. Consequently, a 1.2 mu m thick GaN epitaxial film with a low threading dislocation density of 2.5 x 10 8 cm(-2) and a smooth surface of 0. 38 nm roughness can be achieved on Si substrate. Published by AIP Publishing.