Impurity contamination of GaN epitaxial films from the sapphire, SiC and ZnO substrates

Likely contamination of GaN films by impurities emanating from ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}},$ SiC, and ZnO substrates during growth has been studied by secondary ion mass spectrometry (SIMS) analysis. The defective near-substrate region allows impurities to incorporate more readily as compared to the more perfect crystal as evidenced by increased impurity levels in that region detected by SIMS. The SIMS measurements in GaN layers grown on SiC, ZnO, and sapphire showed large amounts of Si, Zn, and O, respectively, within a region wider than the defective near-substrate layer pointing to the possibility of impurity diffusion at growth temperatures. The qualitative trend observed is fairly clear and significant.