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 〈 1 0 over(1, -) 0 〉 orientation, in contrast to the general observations of 60° complete MDs along 〈 1 1 over(2, -) 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.