Optical and Structural Characterization of Dislocations in GaN Epitaxial Layers

We investigated the defects in GaN heteroepitaxial layers grown on sapphire substrates by hydride vapor phase epitaxy (HVPE) using optical and structural analysis methods, such as cathodolumi-nescence (CL), atomic force microscopy (AFM), and transmission electron microscopy (TEM). We optimized the experimental condition of analytical tools for the defects in GaN and employed the microfabrication technique for sample preparation. The numbers and the positions of etch pits from AFM images exactly corresponded to those of dark spots from CL images, when we compared the defect density of AFM with that of CL results. In addition, we confirmed that the dark spots from CL results were mainly caused by the threading dislocations in GaN interpreting the cross-sectional TEM images.