Published online by Cambridge University Press: 21 February 2011
Cross-sectional Transmission Electron Microscopy (TEM) was used to probe dislocation density and crystallographic orientation relationships in epitaxial GaN layers grown on (0001) sapphire substrates. These Metallo-Organic Chemical Vapor Deposited (MOCVD) structures contained a 200 Å A1N buffer layer. Previous studies1 have incorporated 500 Å (or thicker) A1N buffer layers. It was found that thinner A1N buffer layers may be used without deterioration of GaN crystal quality. Threading dislocation density of ~108 #/cm2 was estimated from bright field micrographs. The relative crystallographic orientations of the substrate and epi-layers was determined by comparing real and simulated electron diffraction patterns. This revealed a 30° ‘twist’ between the basal plane of the sapphire substrate and the AlN/GaN epilayers. XTEM including High Resolution TEM (HRTEM) and HRTEM image simulations are presented.