High-resolution TEM observation of AlN grown on on-axis and off-cut SiC substrates

High-resolution TEM has been carried out on AlN epifilms grown on both on-axis and off-cut SiC substrates to study the state of strain relaxation at the interface and the defects formed in the AlN films. Prismatic stacking faults (PSF) are observed forming at I1 type substrate steps. These PSFs expand into the further grown GaN film and form complicated intersecting configurations in the off-cut sample while they annihilate each other and form enclosed domains at the near-interface region in the on-axis sample. A set of 60° misfit dislocations (MDs) are observed along 〈101¯0〉 orientation, in contrast to the general observations of 60° complete MDs along 〈112¯0〉 orientation reported in literature. These MDs are suggested as geometric partial misfit dislocations which serve both to relax in-plane mismatch and accommodate stacking differences at substrate steps of I2 type.