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 heter ostructures. 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 l ess tensile with stress values near 1 kbar thereafter. We interpret th is as a successive relief of lattice mismatch and thermal stresses cul minating in a catastrophic relief by unknown mechanisms at moderate th icknesses. These data indicate that relaxation processes in these hete rostructures are not as well understood as previously supposed. (C) 19 98 American Institute of Physics. [S0003-6951(98)01845-2].