Defect formation during hetero-epitaxial growth of aluminum nitride thin films on 6H-silicon carbide by gas-source molecular beam epitaxy

Defect formation mechanisms in AlN thin films grown on 6H-SiC(001) substrates have been investigated as a function of film thickness to 180 nm using conventional and high-resolution transmission electron microscopy (HRTEM). The presence of particular Si-terminated steps on the vicinal 6H-SiC surface caused the introduction of planar defects at the initial stage of growth. By contrast, micrographs of films deposited on the on-axis substrate showed a much lower density of defects. Atomistic structural models of the interface and deposited AlN are proposed based on the HRTEM images and the results of companion scanning tunneling microscopy (STM) studies of the vicinal 6H-SiC(001) surface. The introduction of additional defects, which were primarily threading dislocations, was observed with increasing thickness of the AlN films.