TEM Analysis of Microstructures of AlN/sapphire grown by MOCVD

We report on microstructure analysis of aluminum nitride (AlN) epilayers by transmission electron microscopy (TEM). AlN epilayer samples were grown on sapphire substrates by metal organic chemical vapor deposition. Cross section and plan view images were taken by TEM to investigate the threading dislocations. Edge type threading dislocations dominate the total dislocation density. The threading dislocations are greatly reduced by inserting an intermediate layer prior to the growth of high temperature AlN epilayer. The dislocations further reduce with increasing thickness. Our results correlate with the dislocation density estimated from x-ray diffraction analysis.