Trends in residual stress for GaN/AlN/6H-SiC heterostructures

We discuss trends in residual stress as a function of film thickness, growth temperature, and substrate orientation for GaN/AlN/6H-SiC heterostructures. Films are mostly compressive for samples less than about 0.7 mu m thick, are tensile up to about 2 mu m, then abruptly become less tensile with stress values near 1 kbar thereafter. We interpret this as a successive relief of lattice mismatch and thermal stresses culminating in a catastrophic relief by unknown mechanisms at moderate thicknesses. These data indicate that relaxation processes in these heterostructures are not as well understood as previously supposed. (C) 1998 American Institute of Physics. [S0003-6951(98)01845-2].