Influence of Stacking Sequences and Lattice Parameter Differences on the Microstructure of Nonpolar AlN Films Grown on (11(2)over-bar0) 6H-SiC by Plasma-Assisted Molecular Beam Epitaxy

Thanks to close crystalline structures and low lattice mismatches, nonpolar (11 (2) over bar0) 6H-SiC is expected to be a well- adapted substrate for the growth of nonpolar (11 (2) over bar0) III-nitride films. We demonstrate that the local reproduction of the basal planes stacking induces the presence of numerous planar defects (1.3 x 10(6) cm(-1)) in AlN films deposited on (11 (2) over bar0) 6H-SiC. Moreover, the tensile strain of AlN along the [0001] direction results in the cracking of the film for a thickness as low as 100 nm. This fragile plastic relaxation is favored because the only slip systems available for ductile plastic relaxation are pyramidal systems involving a + c dislocations which have a high activation energy.