Structural evolution in epitaxial metalorganic chemical vapor deposition grown GaN films on sapphire

Abstract

The structural evolution of epitaxial GaN layers grown on basal plane sapphire has been studied by atomic force microscopy (AFM), x-ray diffraction, and transmission electron microscopy (TEM). High-temperature growth (1050–1080 °C) on optimized nucleation layers leads to clear, specular films. AFM on the as-grown surface shows evenly spaced monatomic steps indicative of layer by layer growth. AFM measurements show a step termination density of 1.7×108 cm−2 for 5 μm films. This value is in close agreement with TEM measurements of screw and mixed screw-edge threading dislocation density. The total measured threading dislocation density in the 5 μm films is 7×108 cm−2.