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

By using polarization-dependent x-ray absorption spectroscopy at the Ga edg e, we study the growth of GaN on SiC(0001) in the thickness range 0.7-150 n m. 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 int erface 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. (C) 1999 Am erican Institute of Physics. [S0003-6951(99)03722-5].