We report on the successful growth of 3C-SiC/Si and 3C-SiC/SOI heterostructures for the growth of cubic GaN films. Raman results provided moreover direct evidence of the compliant character of the SOI substrate. We show that the GaN surface roughness depends drastically both on the starting SiC surface and its structural quality. Rheed oscillations patterns of beta -GaN grown on thick 3C-SiC epilayers with smooth surfaces were observed.