Evidence for relaxed and high-quality growth of GaN on SiC(0001)

By using polarization-dependent x-ray absorption spectroscopy at the Ga edge, we study the growth of GaN on SiC(0001) in the thickness range 0.7–150 nm. We find that the growth is always relaxed (i.e., nonpseudomorphic) even for the thinnest epilayers, i.e., below the expected critical thickness. No evidence is found for a mixed Ga/Si interface plane, while a C/N mixed interface plane cannot be ruled out. The results are discussed with reference to the electronic structure of the SiC/GaN heterojunction and in particular to band offsets and strain-induced piezoelectric polarization.